[xj] Re: rough idle timing

XJ
1

Hello Chaps,

Hello Chaps,
Chirs and Manfred -

Please help me understand what is going on here. Getting my Jag (any Jag?)
to idle smoothly is the “Holy Grail” for Jag lovers.

  1. What is your exhaust back pressure with the bad CAT??
  2. What is the “normal” exhaust back pressure?? Has anyone measured it at
    idle and at maybe 60mph??
  3. The 20 degree exhaust cam advance, how did you “measure” 20 degrees?
  4. Did the 20 degree exhaust advance help the idle, or was it something
    else, maybe the???
  5. Is it only your exhaust cam that is changed, ie, your intake cam is set
    at “the notch”???
  6. I have ADVANCED my exhaust cam and RETARDED the intake cam. (84S3) How
    many degrees, I don’t know, can only say that they are both off by 1/2 the
    width of the cam setting notch. That is probably 3/32 inches at the notch
    referenced to the proper 90 degree notch setting.
  7. The theory I was told is that this reduces the cams overlap, this reduces
    the amount of exhaust gas left in the cylinder, this results in smoother
    idle. If you have every played with an EGR valve you have seen this
    effect, that is why an EGR is vacuum controlled so it is closed at idle.
  8. So you ask, "Well Tom, is your idle better with this change??) Yes, but
    still not baby smooth. It idles at 600 rpm per its tach. AND is smooth
    only with the idle mixture screw (on the AFM) turned fully down.
    Torque/acceleration seems the same as before. But please note, I did this
    when I re-did the head gasket and the vlves were ground. So, there are too
    many variables that may be at work to clearly show cause and effect. I ALSO
    advanced the ignition timing to by 4 degrees to 21 BTDC. I think I’ll move
    it back to 17 and see what the idle does.
  9. Inquiring minds want to know :slight_smile: Pull me a warm Guinness please.
    Cherio - Tom

Date: Wed, 12 Sep 2001 11:38:06 -0700 (PDT)
From: Chris K linkos@go.com
Subject: Re: [xj] rough idle tuning

My prayers go out to those who were involved in the terrorist incident.
May a wish be granted to the less fortunate involved with this horrible
event…

(Issue: Rough engine idle w. backpressure)

(My result after this process: 99% improvement in idle and reduced engine
noise at higher speeds)

(Corrective measure taken: Advanced exhaust cam roughtly 20 degrees)

Hi Manfred,
Well, the idea you presented to me was very interesting indeed. I have
looked it over what you have said very carefully but cannot draw the same
conclusion of the cams being off time to the crank. Actually, I was the one
who did the installation & removal of the old head =).
Here is my process, maybe you can catch something in it that I did not.

(Start, old head is off)
(during the entire time, I did not check the harmonic balancer, Engine ran
before head removal. This is the reason I thought about this letter, as I
may have made a flaw, but I ruled that out. Timing was checked and at 17
degrees BTDC, erratic however due to serious head damage and erratic idle)

The Process, starting with old head off.

1- Checked to make sure that cylinder #6 (front of engine, cylinder
closest to the cam gears) at TDC, distributor is set at #6 firing.
(I did not change the distributor setting anytime before or until after
engine was assembled completely)

2- Set both intake & exhaust cams to notch on top, bottom of notch
perpendicular to the cam housing sides.

3- Placed on the head, removed the clips from the cam adjustment plates
in order to re-synchronize the cams.

4- Adjusted the plates to match both cams with the crank, so timing was
just right, reasonably equal tension on both sides of chain. Tightened &
locked the tensioner leaving a small amount of flex in the chain.

5- Re-assembled engine
(did not touch the distributor setting)

6- Cranked engine over, it fired up, ran better but still like junk.
Re-checked cams, both aligned pretty much exactly, intake was off a little
bit, not significant to performance, maybe half a millimeter advance.

7- Checked timing, it was EXACTLY at 17degrees BTDC, someone had put a
white mark on the harmonic balancer and it matched up perfectly on 17.

8- Engine runs like crap at less than or equal to 820rpm… shudders,
stalls, has backpressure but will not backfire. I check EVERYTHING again.
Timing, to my knowledge is perfect. Jag manual says it should be perfect.
Compression perfect, ignition perfect, fuel perfect, air flow acceptable.

9- Change a gob of parts that were tested or new, but to no avail.
Re-check the valve clearances 2 times more, timing, fuel, etc… I get
REALLY irritated…

10- Old school textbook says exhaust is retarded resulting in
backpressure. Frustrated and having another spare engine, gave it a shot
and advanced the exhaust several degrees.

9- I am totally perplexed, it worked! My cams are out of alignment…
Totally 100% out of alignment… But it worked and the improvement is
incredible! There is an occasional packpressure, this I figure is probably
due to my O2 sensor, which was recently changed but probably dead because my
old head a VERY rich exhaust due to 3 1/2 leaking exhaust valves.

9.5- Confused, I pulled out the exhaust cam and compared it to my spare
exhaust cam (being sure to mark the cam position!) I do not see any
difference whatsoever, they seem identical…

10- Changed the O2 sensor. Engine is 99% perfect! Except for one noisy
intake tappet (shim must have been cut improperly, sound comes and goes) and
my new torque converter is probably off-balance (resulting in a very
constant slight shake), the engine runs great! Hacked the old O2 sensor
open (it was bad anyways) and found it was fouled. The old head had run
very rich on acceleration destroying my front cat and the O2 sensor (I pray
not my rear cat as well). I will replace BOTH cats for smog this month…
(UGH…THE COST!).

11- Test drive! Took her out to the freeway and for a neighborhood
cruise. Runs quiet with much improved gas mileage and PLENTY of power.
Runs, feels & sounds like an 85 Jag should.

12- Conclusion. Front cat is bad, should get better top speed with a new
one. O2 sensor was dead from previous head emissions. JAG MANUAL WAS
APPARENTLY INCORRECT… Beats me, I really did trust it, I was not out to
prove anything, it just did not work. It was a real pain in the behind
trying to figure out why it was wrong, I assumed it was correct.

After analyzing this letter I realized that it cannot be a problem with
the harmonic balancer, even though I did not check it as I re-assembled the
engine. This is because the old engine had been totally re-built recently,
cheap intake oil seals were installed resulting in chanmber fouling and
ruined valves. The timing was correct to begin with and was the same
afterwards. Cam & crank sync was at least double or triple checked.

I am sure there is a reasonable explanation for this strange event. I am
still pondering it because there is still (very rare) an occasional
backpressure at very low idle, it cannot be the springs or the valves
though.
My hypothesis is that this backpressure is due to noise in the ECU
communication lines. I am making a custom engine harness to shield the
sensors, cables and improving ground connections to various engine parts. I
am adding a larger value electrolytic capacitor to the air flow meter to
improve signal clarity. I shall report the results.

Thank you very much for the harmonic balance key thought. That is a great
issue to keep in mind for those who re-build their engines. There is also
the second woodruff key as I recall, for the crank gear that I was thinking
about.

Chris
Black 85 XJ6 “Michi Korosu”

  • -----Original Message-----
    From: "M. Gottschalch"megott@ufl.edu
    To: "Chris K"linkos@go.com
    Date: Tue Sep 11 16:07:59 PDT 2001
    Subject: Re: [xj] rough idle tuning

Chris,

Who put the head on? Are you sure that when the head was put on, the
timing of BOTH the intake and exhaust cams was set in the correct way.
If you got so much improvement by advancing the exhaust cam, I would
think that the cam timing was somehow screwed up when it was first set.
It might be a good idea to check where the timing actually is set for
both the intake and the exhaust. As a first step check if the TDC mark
on the harmonic balancer is actually in the correct place. Balancers
have been known to go bad, and also the keys that hold the balancers
have been known to shear. This would cause the timing marks to be off
and would upset the setting of the cams. Check by using a stop in the
sparkplug hole. Mark where the pointer sits when the piston touches the
stop, then turn the crank in the opposite direction and mark where the
pointer sits when the piston comes up on the stop again from the
opposite direction. 1/2 way between the two marks is TDC. I am thinking
that you may find that the TDC as measured will not be the mark on the
damper. If the damper mark was off and was used then obviously the cam
timing will be off. Someone on the engine list a while back had a
problem with the key being sheared and was not able to set the spark
timing. It took a while before the problem was found to be the key. It’s
worth taking the time to check.

–
Manfred
63 E FHC
86 XJ6

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End of XJ Digest V2001 #833

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2

Chris,

I too want to get rid of the rough idle. Could your rough idle and hence
backpressure problem to some extent be caused or exacerbated by the bad cat
you claim now to have? You make it sound as if you can adjust the cam in
about 30secs. Could you swap out the bad cat, try the car, set the cam back
and try it again? Would not problems with the exhaust (clogged cat) cause
odd-ball backpressure situations? (maybe various standing waves at different
RPMs?

Let us know!!

Chris Rogers
Atlanta----- Original Message -----
From: “tom graham” tgraham@mindspring.com
To: xj@jag-lovers.org
Sent: Wednesday, September 12, 2001 3:46 PM
Subject: [xj] Re: rough idle timing

Hello Chaps,

Hello Chaps,
Chirs and Manfred -

Please help me understand what is going on here. Getting my Jag (any
Jag?)
to idle smoothly is the “Holy Grail” for Jag lovers.

  1. What is your exhaust back pressure with the bad CAT??
  2. What is the “normal” exhaust back pressure?? Has anyone measured it at
    idle and at maybe 60mph??
  3. The 20 degree exhaust cam advance, how did you “measure” 20 degrees?
  4. Did the 20 degree exhaust advance help the idle, or was it something
    else, maybe the???
  5. Is it only your exhaust cam that is changed, ie, your intake cam is set
    at “the notch”???
  6. I have ADVANCED my exhaust cam and RETARDED the intake cam. (84S3) How
    many degrees, I don’t know, can only say that they are both off by 1/2
    the
    width of the cam setting notch. That is probably 3/32 inches at the notch
    referenced to the proper 90 degree notch setting.
  7. The theory I was told is that this reduces the cams overlap, this
    reduces
    the amount of exhaust gas left in the cylinder, this results in smoother
    idle. If you have every played with an EGR valve you have seen this
    effect, that is why an EGR is vacuum controlled so it is closed at idle.
  8. So you ask, "Well Tom, is your idle better with this change??) Yes,
    but
    still not baby smooth. It idles at 600 rpm per its tach. AND is smooth
    only with the idle mixture screw (on the AFM) turned fully down.
    Torque/acceleration seems the same as before. But please note, I did this
    when I re-did the head gasket and the vlves were ground. So, there are
    too
    many variables that may be at work to clearly show cause and effect. I
    ALSO
    advanced the ignition timing to by 4 degrees to 21 BTDC. I think I’ll
    move
    it back to 17 and see what the idle does.
  9. Inquiring minds want to know :slight_smile: Pull me a warm Guinness please.
    Cherio - Tom

Date: Wed, 12 Sep 2001 11:38:06 -0700 (PDT)
From: Chris K linkos@go.com
Subject: Re: [xj] rough idle tuning

My prayers go out to those who were involved in the terrorist incident.
May a wish be granted to the less fortunate involved with this horrible
event…

(Issue: Rough engine idle w. backpressure)

(My result after this process: 99% improvement in idle and reduced
engine
noise at higher speeds)

(Corrective measure taken: Advanced exhaust cam roughtly 20 degrees)

Hi Manfred,
Well, the idea you presented to me was very interesting indeed. I have
looked it over what you have said very carefully but cannot draw the same
conclusion of the cams being off time to the crank. Actually, I was the
one
who did the installation & removal of the old head =).
Here is my process, maybe you can catch something in it that I did not.

(Start, old head is off)
(during the entire time, I did not check the harmonic balancer, Engine
ran
before head removal. This is the reason I thought about this letter, as I
may have made a flaw, but I ruled that out. Timing was checked and at 17
degrees BTDC, erratic however due to serious head damage and erratic idle)

The Process, starting with old head off.

1- Checked to make sure that cylinder #6 (front of engine, cylinder
closest to the cam gears) at TDC, distributor is set at #6 firing.
(I did not change the distributor setting anytime before or until after
engine was assembled completely)

2- Set both intake & exhaust cams to notch on top, bottom of notch
perpendicular to the cam housing sides.

3- Placed on the head, removed the clips from the cam adjustment plates
in order to re-synchronize the cams.

4- Adjusted the plates to match both cams with the crank, so timing was
just right, reasonably equal tension on both sides of chain. Tightened &
locked the tensioner leaving a small amount of flex in the chain.

5- Re-assembled engine
(did not touch the distributor setting)

6- Cranked engine over, it fired up, ran better but still like junk.
Re-checked cams, both aligned pretty much exactly, intake was off a little
bit, not significant to performance, maybe half a millimeter advance.

7- Checked timing, it was EXACTLY at 17degrees BTDC, someone had put a
white mark on the harmonic balancer and it matched up perfectly on 17.

8- Engine runs like crap at less than or equal to 820rpm… shudders,
stalls, has backpressure but will not backfire. I check EVERYTHING again.
Timing, to my knowledge is perfect. Jag manual says it should be perfect.
Compression perfect, ignition perfect, fuel perfect, air flow acceptable.

9- Change a gob of parts that were tested or new, but to no avail.
Re-check the valve clearances 2 times more, timing, fuel, etc… I get
REALLY irritated…

10- Old school textbook says exhaust is retarded resulting in
backpressure. Frustrated and having another spare engine, gave it a shot
and advanced the exhaust several degrees.

9- I am totally perplexed, it worked! My cams are out of alignment…
Totally 100% out of alignment… But it worked and the improvement is
incredible! There is an occasional packpressure, this I figure is
probably
due to my O2 sensor, which was recently changed but probably dead because
my
old head a VERY rich exhaust due to 3 1/2 leaking exhaust valves.

9.5- Confused, I pulled out the exhaust cam and compared it to my spare
exhaust cam (being sure to mark the cam position!) I do not see any
difference whatsoever, they seem identical…

10- Changed the O2 sensor. Engine is 99% perfect! Except for one noisy
intake tappet (shim must have been cut improperly, sound comes and goes)
and
my new torque converter is probably off-balance (resulting in a very
constant slight shake), the engine runs great! Hacked the old O2 sensor
open (it was bad anyways) and found it was fouled. The old head had run
very rich on acceleration destroying my front cat and the O2 sensor (I
pray
not my rear cat as well). I will replace BOTH cats for smog this month…
(UGH…THE COST!).

11- Test drive! Took her out to the freeway and for a neighborhood
cruise. Runs quiet with much improved gas mileage and PLENTY of power.
Runs, feels & sounds like an 85 Jag should.

12- Conclusion. Front cat is bad, should get better top speed with a
new
one. O2 sensor was dead from previous head emissions. JAG MANUAL WAS
APPARENTLY INCORRECT… Beats me, I really did trust it, I was not out to
prove anything, it just did not work. It was a real pain in the behind
trying to figure out why it was wrong, I assumed it was correct.

After analyzing this letter I realized that it cannot be a problem with
the harmonic balancer, even though I did not check it as I re-assembled
the
engine. This is because the old engine had been totally re-built
recently,
cheap intake oil seals were installed resulting in chanmber fouling and
ruined valves. The timing was correct to begin with and was the same
afterwards. Cam & crank sync was at least double or triple checked.

I am sure there is a reasonable explanation for this strange event. I
am
still pondering it because there is still (very rare) an occasional
backpressure at very low idle, it cannot be the springs or the valves
though.
My hypothesis is that this backpressure is due to noise in the ECU
communication lines. I am making a custom engine harness to shield the
sensors, cables and improving ground connections to various engine parts.
I
am adding a larger value electrolytic capacitor to the air flow meter to
improve signal clarity. I shall report the results.

Thank you very much for the harmonic balance key thought. That is a
great
issue to keep in mind for those who re-build their engines. There is also
the second woodruff key as I recall, for the crank gear that I was
thinking
about.

Chris
Black 85 XJ6 “Michi Korosu”

  • -----Original Message-----
    From: "M. Gottschalch"megott@ufl.edu
    To: "Chris K"linkos@go.com
    Date: Tue Sep 11 16:07:59 PDT 2001
    Subject: Re: [xj] rough idle tuning

Chris,

Who put the head on? Are you sure that when the head was put on, the
timing of BOTH the intake and exhaust cams was set in the correct way.
If you got so much improvement by advancing the exhaust cam, I would
think that the cam timing was somehow screwed up when it was first set.
It might be a good idea to check where the timing actually is set for
both the intake and the exhaust. As a first step check if the TDC mark
on the harmonic balancer is actually in the correct place. Balancers
have been known to go bad, and also the keys that hold the balancers
have been known to shear. This would cause the timing marks to be off
and would upset the setting of the cams. Check by using a stop in the
sparkplug hole. Mark where the pointer sits when the piston touches the
stop, then turn the crank in the opposite direction and mark where the
pointer sits when the piston comes up on the stop again from the
opposite direction. 1/2 way between the two marks is TDC. I am thinking
that you may find that the TDC as measured will not be the mark on the
damper. If the damper mark was off and was used then obviously the cam
timing will be off. Someone on the engine list a while back had a
problem with the key being sheared and was not able to set the spark
timing. It took a while before the problem was found to be the key.
It’s
worth taking the time to check.

–
Manfred
63 E FHC
86 XJ6

GO.com Mail
Get Your Free, Private E-mail at http://mail.go.com

===================================================
The archives and FAQ will answer many queries on the XJ series…
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End of XJ Digest V2001 #833

===================================================
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Archives: Jag-lovers Forums - Jag-lovers

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3

Sorry, I meant to send this to the group, forgot to change the address…-----Original Message-----
From: “Chris K”<@Makoto_Kino>
To: "tom graham"tgraham@mindspring.com
Date: Wed Sep 12 16:11:31 PDT 2001
Subject: Re: [xj] Re: rough idle timing

Hi Tom,
Well, I too started with a good engine. Replaced my valve guides, valves and re-ground them. I only intend on using this head until I can re-build another engine to MINT condition for a proper swap.

I have tested most systems (not ALL of them, though I am working towards that in this project). Systems tested/verified
Fuel, Intake, Exhaust (somewhat faulty), ignition, compression, timing. I still need to test/verify my ECU which I AM going to change, I got a lead on a working one for dirt cheap so I figured, what the heck.

The way I see it, no car hot off the press SHOULD have a bad idle. Even a FIAT should idle good! After all, it is a new car, and Jaguar as a matter of fact had BETTER idle nicely, they’re co costly! After re-building a replacement head (by hand no less), the idle was horrid, at specifications, it stalled, shuddered and sometimes even stalled. I set out to change anything and find what caused my junk idle.

Now, “back pressure” as I define it (and as well as my textbook) is a suction on the exhaust pipe, that’s right, suction. If you have it, you will know what I mean. Here’s how to test that.
Use a cloth, paper napkin, plastic bag… whatever and hold it loosely in front of one of the mufflers, if you have back pressure, it will occasionally suck the cloth into the muffler, it will suck it in quite hard. No back pressure, the cloth will stay out and be blown from the muffler. There is NO good backpressure, it’s bad. This means that a cylinder’s exhaust valve is staying open too long and the engine is sucking in exhaust during the intake stroke. If you have a shop scope, this should be verifiable because the result is a huge lack of power to that cylinder and any other that sucks in exhaust, as a matter of fact. This causes the engine to shudder (in my case).

If you get backpressure at 60MPH, you’ve got a BIG problem, that can be numerous things but boy I don’t think the straight 6 or any engine for that matter can get to that speed with backpressure! If so, it would be suicidal to the emission control system and would probably damage the engine. If there was, back pressure at such a speed, it would in my guess be bad valve springs.

I am waiting for my new cat to come in the mail, that will be a few days due to this “incident”. My bad cat does not seem to be a huge problem since at high speeds, I do not level off in power. It is bad however since it can cause other problems.

The 20 degree cam advance was a rotation of the cam from the manufacturer specified position (which is cam notch at 90 degrees, pointing straight up)

I only advanced the exhaust, not the intake. I was asking about that if it is good to just advance 1 because the split overlap (time at which both valves are open) is decreased. The exhaust valve closes sooner.

I did not choose to retard the intake because this COULD result in backfire. That I could really do without. The engine aspiration seems to be fine, no backfire so I left the intake cam alone. Now, from original setting (factory), NEVER advance just the intake, this is really not necessary in any case I can imaging and can cause immediate and massive valve destruction. The gap between the 2 valves is quite small during exhaust/intake. An advance in the exhaust is suitable to reduce split overlap.
Retarding the intake and advancing the exhaust does reduce split overlap, maybe this has somthing as well, I lowered my overlap with only the exhaust cam
It sounds like the advance and retard was around 5 degrees per cam in your case a total of 10 degrees to the exhaust can only would probably yield the same result, but this is un-verified by myself.

You have a very interesting case there, do you know your compression? I’m rather curious. Mine was about 180 as I recall, I will check again and record later. Some people have compression at around 150, 160, etc. This may have something to do with the end result.

EGRs… Heh I had that on a FORD escort a long time ago… I have nothing to say for those things except “added stuff”.

Thanks for in info on the split overlap shift, I’ll see if I can find any information on the use of such a method. Maybe one day when I have the energy I will try removing those came overs again…arrrrgh…

Chris
Black 85 XJ6 “Michi Korosu”

Hello Chaps,
Chirs and Manfred -

Please help me understand what is going on here. Getting my Jag (any Jag?)
to idle smoothly is the “Holy Grail” for Jag lovers.

  1. What is your exhaust back pressure with the bad CAT??

  2. What is the “normal” exhaust back pressure?? Has anyone measured it at
    idle and at maybe 60mph??

  3. The 20 degree exhaust cam advance, how did you “measure” 20 degrees?

  4. Did the 20 degree exhaust advance help the idle, or was it something
    else, maybe the???

  5. Is it only your exhaust cam that is changed, ie, your intake cam is set
    at “the notch”???

  6. I have ADVANCED my exhaust cam and RETARDED the intake cam. (84S3) How
    many degrees, I don’t know, can only say that they are both off by 1/2 the
    width of the cam setting notch. That is probably 3/32 inches at the notch
    referenced to the proper 90 degree notch setting.

  7. The theory I was told is that this reduces the cams overlap, this reduces
    the amount of exhaust gas left in the cylinder, this results in smoother
    idle. If you have every played with an EGR valve you have seen this
    effect, that is why an EGR is vacuum controlled so it is closed at idle.

  8. So you ask, "Well Tom, is your idle better with this change??) Yes, but
    still not baby smooth. It idles at 600 rpm per its tach. AND is smooth
    only with the idle mixture screw (on the AFM) turned fully down.
    Torque/acceleration seems the same as before. But please note, I did this
    when I re-did the head gasket and the vlves were ground. So, there are too
    many variables that may be at work to clearly show cause and effect. I ALSO
    advanced the ignition timing to by 4 degrees to 21 BTDC. I think I’ll move
    it back to 17 and see what the idle does.

  9. Inquiring minds want to know :slight_smile: Pull me a warm Guinness please.
    Cherio - Tom

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4

Hi Chris,
I seriously doubt that the cat has anything to do with the problem. I am going to change it as a matter of fact along with my ECU. The cam is adjustable but no way is that 30seconds! I hate dealing with the cams due to the huge mess and pain cleaning off the gasket/re-sealing, etc… I was condisering hollowing out this cat in the meantime, just for a test because I need the O2 sensor on there and the cat is history. However, if the cat was causing such a problem, then I should have high RPM power drop off because the exhaust would be blocked resulting in a great change in engine aspiration. I drive on the freeway fine and the engine revs hard so there probably is not much blockage. Also at low RPM, the cat junk in the cat does not clatter around so there is no variation in the restriction. I’m a perfectionist, NO blockage is good and anything less than decent for my jag, I’ll pursue to no end =), I will even risk the engine if it comes to it but I probably will not lose it. So I’ll continue my experimentation. Don’t worry, I’ll report anything new. =)

Oh and Chris, try giving me the symptoms, as many details as possible, you may not have the same problem as I. You may just have a bad O2 sensor, those foul quite easily in the Jag and can cause a very similar problem, not as bad as mine though.

Chris
Black 85 XJ6 “Michi Korosu”>Chris,

I too want to get rid of the rough idle. Could your rough idle and hence
backpressure problem to some extent be caused or exacerbated by the bad cat
you claim now to have? You make it sound as if you can adjust the cam in
about 30secs. Could you swap out the bad cat, try the car, set the cam back
and try it again? Would not problems with the exhaust (clogged cat) cause
odd-ball backpressure situations? (maybe various standing waves at different
RPMs?

Let us know!!

Chris Rogers
Atlanta

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5

Chris,

To the rest of the listers we probably sounds like we are one person talking
to himself …

My car has a rough idle when I pull up to the stoplight. It shakes the
entire car sometimes and sounds rather like a tractor. (long stroke?)
My O2 sensor was recently changed with not much result. I have yet to try
the regapped plugs mentioned earlier. I no longer have a front cat on my car
and I don’t know the condition of the rear one. I do use oil, I think both
through the tailpipe and out the front of the engine seals. My idle seems to
smooth out as soon as I put a tad bit more gas to it, so I have been tempted
to tweak the idle a bit higher. Current idle appears to be set about where
it should be…assuming my tach is accurate.

I have yet to really try to track down the problem…what should I try?
Regap the plugs first?

Thanks for the assistance.

Chris Rogers
Atlanta----- Original Message -----
From: “Chris K” linkos@go.com
To: xj@jag-lovers.org
Sent: Wednesday, September 12, 2001 7:25 PM
Subject: Re: Re: [xj] Re: rough idle timing

Hi Chris,
I seriously doubt that the cat has anything to do with the problem. I am
going to change it as a matter of fact along with my ECU. The cam is
adjustable but no way is that 30seconds! I hate dealing with the cams due
to the huge mess and pain cleaning off the gasket/re-sealing, etc… I was
condisering hollowing out this cat in the meantime, just for a test because
I need the O2 sensor on there and the cat is history. However, if the cat
was causing such a problem, then I should have high RPM power drop off
because the exhaust would be blocked resulting in a great change in engine
aspiration. I drive on the freeway fine and the engine revs hard so there
probably is not much blockage. Also at low RPM, the cat junk in the cat
does not clatter around so there is no variation in the restriction. I’m a
perfectionist, NO blockage is good and anything less than decent for my jag,
I’ll pursue to no end =), I will even risk the engine if it comes to it but
I probably will not !
lose it. So I’ll continue my experimentation. Don’t worry, I’ll report
anything new. =)

Oh and Chris, try giving me the symptoms, as many details as possible, you
may not have the same problem as I. You may just have a bad O2 sensor,
those foul quite easily in the Jag and can cause a very similar problem, not
as bad as mine though.

Chris
Black 85 XJ6 “Michi Korosu”

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6

For whomever recommended opening the spark plug gap as a remedy for rough
idle…Thank you!

My 1987 XJ6 has had almost every jag mechanic in Northern Virginia try to
eliminate the rough idle. New head, new cams, new everything else over the
years. Rough idle always there.

Just for fun, I opened the plug gap to .042 last night and it made a
remarkable difference. Still a little roughness but nothing like before.
And the engine seems to have lost that little hesitation upon acceleration.

This seems to good to be true, so a few days of driving will tell. But for
now, I’m quite pleased with such a simple solution to this long lasting
problem.

jlrm===================================================
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7

Hello Chris,

Heh, it is interesting to use the same name in replies, thank goodness the Email addresses are different!

Ok, from what I can tell, it sounds almost exactly like my problem before I started on my engine… Not too good. The spark plug gap is not too significant if set properly already. Although it does help a little to buy you some time if the engine is weak, gapping them closer may help burn the fuel a bit better. If there is oil in the tail, that is quite bad especially if you mean liquid, that is pretty much fatal. It can mean either bad piston rings or bad valves. If there is no constant smoke, the head gasket is probably ok.
If it smokes on acceleration, intake valve guides are probably quite shot, smokes early in the morning (start, quickly rev engine, punch the gas, puff of smoke) then the intake seals are probably bad, leaking slowly.

My problem was that the intake valve seals were leaking oil, this in turn fouled my intake valves, which fouled my cylinders which killed my new O2 sensor, ruined my exhaust valves and killed my front cat (whew! and good lord that was horrible). I was prompted to change my engine head because of the embaressment of such a violent shaking when at a stop, also no power on acceleration, this due to 1 dead valve, 3 others leaking. The pickup was about the same as a 3 cylinder jag, hah.

Here is where I would start looking, in this situation.
If you have awful acceleration, your compression is more than likely bad but I’ll not draw to that conclusion yet, with luck it will be something else.

1- check the compression if you have a compression checker. If not, then try pulling Fuel Injector plugs one at a time and note the RPM change. The engine should lose a constant RPM for each FI plug. If one of them does not change anything, then that cylinder is probably either leaking somehow or the injector is plugged.

2- If there is loss of compression and/or one or more of the injectors do not lose the same RPM, try removing/checking the spark plugs for oil (black fuzzy carbon) or if they are thick, crusty brown particularly on one side (in my case, this was burned up oil). Note if any of the plugs have different coatings on them. This is how mine looked, 1 had oil, others were crusty brown, thicker on 1 side. If you see oil on one of them, try taking off the exhaust manifold to see if the oil is coming from the head and from which chamber. This should be evident by blackness and thickness of the carbon. If there is oil (thick fuzzy carbon) in 1 or more cylinders, then chances are your head is leaking oil, if you have high mileage, it may be the guides leaking, lower mileage, probably the intake seals.

If there is good compression, clean plugs, and the injectors do not lose the same RPM, check for dirty injectors or bad injectors, a 9volt battery across an injector should open it. If dirty, that’s kinda a pain, I won’t go there unless this is a possibility.

Now, chances are if you are using oil and it is out the tail, the O2 sensor is already history… Just hope the rear cat is ok, those are quite costly. This is the result of too rich a mixture or oil fouling. Other oil leaks are usually the pipes from the head, cam housing seals, timing cover seal, crankshaft seals or in the worst case, head gasket.

Before I can go any further, let me know what your results are on the compression, plugs and or injectors, and we can work from there.

If your head is bad (leaking valves/guides, oil coming out the engine head), then be prepared to either live with it, be very dedicated and patient mechanic or spend a ton of cash for some other unfortunate soul to deal with it… I changed mine myself… WHEW!! whadda job… I had a spare engine head pre-restored and ready to swap, saved a LOT of time =). The total work is enough to make you pity the official jag mechanic! I would seriously recommend the machine shop take care of valve grinding and valve guide replacement, it’s difficult, irritating and boring restoring those heads the machine shop is well worth the few bucks for the time and energy it takes to re-do those heads.

If I can find the time, I will probably make an illustrated web page to help others with the same situation as mine.

Chris
Black 85 XJ6 “Michi Korosu”___________________________________________________
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8

Jerry, what was the gap before?–
Alex
79xj6L SII (BRG + wires)
86xj6 SIII (Black)
61 Sprite MkII (Red)
Menlo Park, Calif.

Jerry Mowery wrote:

For whomever recommended opening the spark plug gap as a remedy for rough
idle…Thank you!

My 1987 XJ6 has had almost every jag mechanic in Northern Virginia try to
eliminate the rough idle. New head, new cams, new everything else over the
years. Rough idle always there.

Just for fun, I opened the plug gap to .042 last night and it made a
remarkable difference. Still a little roughness but nothing like before.
And the engine seems to have lost that little hesitation upon acceleration.

This seems to good to be true, so a few days of driving will tell. But for
now, I’m quite pleased with such a simple solution to this long lasting
problem.

jlrm

===================================================
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9

I’m not sure if this will help, but… I have been chasing a rough idle
on our Ford Explorer for quite a while. I decided to take to emissions to
get an idea of what was going on. I found my %co was low (idle and load),
but my HC at idle was 1420 (104 under load).

I then double/tipple checked wires and plugs (I did change the gap from 56
down to 50… I used 56 instead of the recommended 50-54 to keep pinging
down) and still had the issue. While poking around I noticed it sounded
like there was an exhaust leak. After replacing the exhaust manifold and
checking for any other leaks I decided to check for a leak in the motor. I
did a compression check and found the #6 cylinder (back cylinder on our v6)
only had 60psi in it while the rest had 160-170psi (not bad for 246k
miles). This is after I took it to other shops to figure out what was
going on and they were blaming wires, wrong plugs, over gapping plugs, bad
sensors, bad TPS, MAS etc…

so, what I’m getting at is don’t forget the basics… Need Gas, Air, Spark,
and compression to work… (I forgot about compression… $300 in parts
later I remembered and checked it)

Looks like I need to finish putting in that rear end in our '73 SI xj6 so I
can take the motor on the explorer apart and rebuild it…

Good Luck, and Good Hunting

~Mark

Mark
@Mark_Strickland
http://mark.legendz.com
Off-Road and Motorcycle Information, Pictures and Movies===================================================
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10

Hi Tom,

That’s a thought, good way to check the rear cat (in my case) with a pressure meter on the O2 sensor. I’ll give that a shot later.

I suppose my definition of back pressure isn’t really a book definition, there always should be some vacuum in the line to help pull the exhaust into the cylinder. From what I have, it just sucks the fuel in and right on out the exhaust. Too much vacuum…

Awful to hear about the valves, I ALMOST had that same experience while adjusting my tappet shims. I set the exhaust cam to a different timing mark I had made earlier… Fortunately it was so out of phase that the valves came nowhere near each other. I checked on my spare head though, the space between the intake/exhaust, there is very little to play with as we well know. That is why I decided not to fool with the intake, only 1 at a time and only reducing split overlap. I am sure that if anyone, we will NOT forget to keep the timing chain attached when cranking =).

As far as the precise advance goes, I pretty much approximated it, I did not calculate anything precisely.
The 20 degree change is relative to either the notch or the cam shaft housing walls. Anywhere that starts at 90 or 0 degrees.
If you really are a perfectionist, there are more cumbersome mathematical strategies to finding a precise angle, but not even the Jaguar is that precise so an approximation will have to do anyways. Here is a little on roughly calculating an angle.

Now if you want to get into that math, pi * diameter = circumference. Now just go out to a local office supply store and find a protractor, you can use any (the more costly, the more precise in general), as long as the marks are clear enough. Find the circumference of the protractor.
To make things a bit short (I don’t want to get too much into geometry…) Measure the distance between 0 to the degree desired along the top of the protractor, and this should be approximate to the cam proportion.

This is the equality
([protractor] dist1/circ1 = dist2/circ2 [cam])

this method may be a bit better than eyeballing.

Now, I don’t seriously recommend the math, I never liked it because it sucks the fun out of working on a car (for me anyways) =). Just an eyeball approximation should be sufficient. Most anyone can see 45 degrees and most can estimate 10 degrees with good accuracy (by 1 or 2 degrees). I made the approximate that every cam plate notch is roughly 5 degrees. I eyeballed the position relative the the sides of the cam housing.

I do not see exactly where the loss of power may have come it, not right offhand anyways. This may be due to the distributor setting and the type of fuel used. The cam change does not seem significant enough to cause any serious alteration in power.

I guess I am a bit “all or nothing” about my Jag, I know what processes do in theory so I attempt them. I suppose that independent mechanic was much the same way. However, it seems to me that the replacement of the EGR is all that extra air system added to help burn off the emissions gas. (and work the valves, cats) I believe the air system gives the engine more power because there is more oxygen for combustion, less burnable gas would leave the cylinder if more burned. The emissions are taken care of outside the engine. Of course if the air system fails (like mine did), all that junk gets stuffed into the front cat and probably melts it (like mine did). Maybe the front cat is a sacrifical device, in case the air system fails, cheaper than the rear cat? That’s my only guess.

Chris
Black 85 XJ6 “Michi Korosu”-----Original Message-----
From: "tom graham"tgraham@mindspring.com
To: “Chris K”<@Makoto_Kino>
Date: Wed Sep 12 22:22:01 PDT 2001
Subject: Re: [xj] Re: rough idle timing

Hi Chris,
Thanks for your great reply. My definition of back pressure , I guess
unique to me:-) is the pressure resulting from a plugged exhaust system. On
my old Ford I put a gauge in temporarily in place of the O2 sensor and
measured 1 psi at idle and 4 psi when I gunned the engine. I’m going to put
a gauge on my Jag ahead of the O2 sensor and measure the pressure. I’m also
going to try the loose cloth thing near the tail pipe.

Yes I had a real learning experience replacing my Jag head. I’ve had the
head off three times. Twice this spring because I did the very stupid
mistake of cranking the engine when setting up the cams and crunching valves
together!!! I could not believe it, so careless!!! ESPECIALLY when doing
it the second time, un-believable. If nothing else, I no longer dread
pulling the head, it’s just another long chore. But I still get very
nervous about playing with cam timing :slight_smile: The lesson learned is do not turn
the engine without both cams bolted onto the chain.

I do not know what my compression is. I need to get the type of gauge that
screws into the plug hole.

I like your 20 degree change, how did you measure it, how did you set it up
relative to the cam notch?? I think this may be better than my change of
both cams because I have feeling that the car lost some low end torque. I
have had no backfiring. And, as I said, I also advanced the ignition
timing 4 degrees so it is hard to know what is doing what. How “far” did
you move the exhaust cam ??? I can’t look at it and guess 20 degrees.
Let’s think about it. The notch is 1/4 inch wide ???, and the cam diameter
at the notch is ??? 2 inches??? If so, then the cam circumference is 6.28
inches. A 1/4 inch would be .040 of that circumference or 14 degrees. We’d
have to have the exact dimensions of the notch and diameter to properly
figure this.

This EGR thing. It’s only purpose is to introduce inert exhaust into the
cylinder and this keeps the combustion temperature low enough to keep NOx
emissions low. Our Jags do not have and EGR as you well know. An old
independent Jag mechanic told me that the reason Jag does not have the EGR
is because it instead overlaps the cams to allow some exhaust to remain in
the cylinder. And this is the reason the idle is lumpy. He said to move
both cams and the idle would be much improved. This was about 8 years ago I
heard this. Since then I have asked around about this, even here on Jag
lovers, and the only answer was no it would not help but no they had not
tried it. So I tried it last spring but am unsure of the results. You can
imagine my excitement when I read your posting bout doing almost the same
thing :slight_smile:

What I should now do is make that exhaust pressure measurement, then move
the intake cam back to factory and move the exhaust cam more advanced,
measure again the exhaust pressure, change the ignition timing back to 17
degrees. And make a compression check. Maybe I’ll do this Friday. BTW I
have tried plug gap to .040 but no better idle. I’ll let you know.

Regards - Tom

----- Original Message -----
From: Chris K <@Makoto_Kino>
To: tom graham tgraham@mindspring.com
Sent: Wednesday, September 12, 2001 4:11 PM
Subject: Re: [xj] Re: rough idle timing

Hi Tom,
Well, I too started with a good engine. Replaced my valve guides, valves
and re-ground them. I only intend on using this head until I can re-build
another engine to MINT condition for a proper swap.

I have tested most systems (not ALL of them, though I am working towards
that in this project). Systems tested/verified
Fuel, Intake, Exhaust (somewhat faulty), ignition, compression, timing. I
still need to test/verify my ECU which I AM going to change, I got a lead on
a working one for dirt cheap so I figured, what the heck.

The way I see it, no car hot off the press SHOULD have a bad idle. Even a
FIAT should idle good! After all, it is a new car, and Jaguar as a matter
of fact had BETTER idle nicely, they’re co costly! After re-building a
replacement head (by hand no less), the idle was horrid, at specifications,
it stalled, shuddered and sometimes even stalled. I set out to change
anything and find what caused my junk idle.

Now, “back pressure” as I define it (and as well as my textbook) is a
suction on the exhaust pipe, that’s right, suction. If you have it, you
will know what I mean. Here’s how to test that.
Use a cloth, paper napkin, plastic bag… whatever and hold it loosely in
front of one of the mufflers, if you have back pressure, it will
occasionally suck the cloth into the muffler, it will suck it in quite hard.
No back pressure, the cloth will stay out and be blown from the muffler.
There is NO good backpressure, it’s bad. This means that a cylinder’s
exhaust valve is staying open too long and the engine is sucking in exhaust
during the intake stroke. If you have a shop scope, this should be
verifiable because the result is a huge lack of power to that cylinder and
any other that sucks in exhaust, as a matter of fact. This causes the
engine to shudder (in my case).

If you get backpressure at 60MPH, you’ve got a BIG problem, that can be
numerous things but boy I don’t think the straight 6 or any engine for that
matter can get to that speed with backpressure! If so, it would be suicidal
to the emission control system and would probably damage the engine. If
there was, back pressure at such a speed, it would in my guess be bad valve
springs.

I am waiting for my new cat to come in the mail, that will be a few days
due to this “incident”. My bad cat does not seem to be a huge problem since
at high speeds, I do not level off in power. It is bad however since it can
cause other problems.

The 20 degree cam advance was a rotation of the cam from the manufacturer
specified position (which is cam notch at 90 degrees, pointing straight up)

I only advanced the exhaust, not the intake. I was asking about that if
it is good to just advance 1 because the split overlap (time at which both
valves are open) is decreased. The exhaust valve closes sooner.

I did not choose to retard the intake because this COULD result in
backfire. That I could really do without. The engine aspiration seems to
be fine, no backfire so I left the intake cam alone. Now, from original
setting (factory), NEVER advance just the intake, this is really not
necessary in any case I can imaging and can cause immediate and massive
valve destruction. The gap between the 2 valves is quite small during
exhaust/intake. An advance in the exhaust is suitable to reduce split
overlap.
Retarding the intake and advancing the exhaust does reduce split overlap,
maybe this has somthing as well, I lowered my overlap with only the exhaust
cam
It sounds like the advance and retard was around 5 degrees per cam in your
case a total of 10 degrees to the exhaust can only would probably yield the
same result, but this is un-verified by myself.

You have a very interesting case there, do you know your compression? I’m
rather curious. Mine was about 180 as I recall, I will check again and
record later. Some people have compression at around 150, 160, etc. This
may have something to do with the end result.

EGRs… Heh I had that on a FORD escort a long time ago… I have nothing
to say for those things except “added stuff”.

Thanks for in info on the split overlap shift, I’ll see if I can find any
information on the use of such a method. Maybe one day when I have the
energy I will try removing those came overs again…arrrrgh…

Chris
Black 85 XJ6 “Michi Korosu”

Hello Chaps,
Chirs and Manfred -

Please help me understand what is going on here. Getting my Jag (any Jag?)
to idle smoothly is the “Holy Grail” for Jag lovers.

  1. What is your exhaust back pressure with the bad CAT??

  2. What is the “normal” exhaust back pressure?? Has anyone measured it at
    idle and at maybe 60mph??

  3. The 20 degree exhaust cam advance, how did you “measure” 20 degrees?

  4. Did the 20 degree exhaust advance help the idle, or was it something
    else, maybe the???

  5. Is it only your exhaust cam that is changed, ie, your intake cam is set
    at “the notch”???

  6. I have ADVANCED my exhaust cam and RETARDED the intake cam. (84S3) How
    many degrees, I don’t know, can only say that they are both off by 1/2 the
    width of the cam setting notch. That is probably 3/32 inches at the notch
    referenced to the proper 90 degree notch setting.

  7. The theory I was told is that this reduces the cams overlap, this
    reduces
    the amount of exhaust gas left in the cylinder, this results in smoother
    idle. If you have every played with an EGR valve you have seen this
    effect, that is why an EGR is vacuum controlled so it is closed at idle.

  8. So you ask, "Well Tom, is your idle better with this change??) Yes, but
    still not baby smooth. It idles at 600 rpm per its tach. AND is smooth
    only with the idle mixture screw (on the AFM) turned fully down.
    Torque/acceleration seems the same as before. But please note, I did this
    when I re-did the head gasket and the vlves were ground. So, there are too
    many variables that may be at work to clearly show cause and effect. I
    ALSO
    advanced the ignition timing to by 4 degrees to 21 BTDC. I think I’ll move
    it back to 17 and see what the idle does.

  9. Inquiring minds want to know :slight_smile: Pull me a warm Guinness please.
    Cherio - Tom

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Get Your Free, Private E-mail at http://mail.go.com

===================================================
The archives and FAQ will answer many queries on the XJ series…
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Archives: Jag-lovers Forums - Jag-lovers

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11

Hi Tom,

That’s a thought, good way to check the rear cat (in my case) with a pressure meter on the O2 sensor. I’ll give that a shot later.

I suppose my definition of back pressure isn’t really a book definition, there always should be some vacuum in the line to help pull the exhaust into the cylinder. From what I have, it just sucks the fuel in and right on out the exhaust. Too much vacuum…

Awful to hear about the valves, I ALMOST had that same experience while adjusting my tappet shims. I set the exhaust cam to a different timing mark I had made earlier… Fortunately it was so out of phase that the valves came nowhere near each other. I checked on my spare head though, the space between the intake/exhaust, there is very little to play with as we well know. That is why I decided not to fool with the intake, only 1 at a time and only reducing split overlap. I am sure that if anyone, we will NOT forget to keep the timing chain attached when cranking =).

As far as the precise advance goes, I pretty much approximated it, I did not calculate anything precisely.
The 20 degree change is relative to either the notch or the cam shaft housing walls. Anywhere that starts at 90 or 0 degrees.
If you really are a perfectionist, there are more cumbersome mathematical strategies to finding a precise angle, but not even the Jaguar is that precise so an approximation will have to do anyways. Here is a little on roughly calculating an angle.

Now if you want to get into that math, pi * diameter = circumference. Now just go out to a local office supply store and find a protractor, you can use any (the more costly, the more precise in general), as long as the marks are clear enough. Find the circumference of the protractor.
To make things a bit short (I don’t want to get too much into geometry…) Measure the distance between 0 to the degree desired along the top of the protractor, and this should be approximate to the cam proportion.

This is the equality
([protractor] dist1/circ1 = dist2/circ2 [cam])

this method may be a bit better than eyeballing but I doubt it needs anywhere near this sort of precision.

Now, I don’t seriously recommend the math, I never liked it because it sucks the fun out of working on a car (for me anyways) =). Just an eyeball approximation should be sufficient. Most anyone can see 45 degrees and most can estimate 10 degrees with good accuracy (by 1 or 2 degrees). I made the approximate that every cam plate notch is roughly 5 degrees. I eyeballed the position relative the the sides of the cam housing.

I do not see exactly where the loss of power may have come it, not right offhand anyways. This may be due to the distributor setting and the type of fuel used. The cam change does not seem significant enough to cause any serious alteration in power.

I guess I am a bit “all or nothing” about my Jag, I know what processes do in theory so I attempt them. I suppose that independent mechanic was much the same way. However, it seems to me that the replacement of the EGR is all that extra air system added to help burn off the emissions gas. (and work the valves, cats) I believe the air system gives the engine more power because there is more oxygen for combustion, less burnable gas would leave the cylinder if more burned. The emissions are taken care of outside the engine. Of course if the air system fails (like mine did), all that junk gets stuffed into the front cat and probably melts it (like mine did). Maybe the front cat is a sacrifical device, in case the air system fails, cheaper than the rear cat? That’s my only guess.

Chris
Black 85 XJ6 “Michi Korosu”-----Original Message-----
From: "tom graham"tgraham@mindspring.com
To: “Chris K”<@Makoto_Kino>
Date: Wed Sep 12 22:22:01 PDT 2001
Subject: Re: [xj] Re: rough idle timing

Hi Chris,
Thanks for your great reply. My definition of back pressure , I guess
unique to me:-) is the pressure resulting from a plugged exhaust system. On
my old Ford I put a gauge in temporarily in place of the O2 sensor and
measured 1 psi at idle and 4 psi when I gunned the engine. I’m going to put
a gauge on my Jag ahead of the O2 sensor and measure the pressure. I’m also
going to try the loose cloth thing near the tail pipe.

Yes I had a real learning experience replacing my Jag head. I’ve had the
head off three times. Twice this spring because I did the very stupid
mistake of cranking the engine when setting up the cams and crunching valves
together!!! I could not believe it, so careless!!! ESPECIALLY when doing
it the second time, un-believable. If nothing else, I no longer dread
pulling the head, it’s just another long chore. But I still get very
nervous about playing with cam timing :slight_smile: The lesson learned is do not turn
the engine without both cams bolted onto the chain.

I do not know what my compression is. I need to get the type of gauge that
screws into the plug hole.

I like your 20 degree change, how did you measure it, how did you set it up
relative to the cam notch?? I think this may be better than my change of
both cams because I have feeling that the car lost some low end torque. I
have had no backfiring. And, as I said, I also advanced the ignition
timing 4 degrees so it is hard to know what is doing what. How “far” did
you move the exhaust cam ??? I can’t look at it and guess 20 degrees.
Let’s think about it. The notch is 1/4 inch wide ???, and the cam diameter
at the notch is ??? 2 inches??? If so, then the cam circumference is 6.28
inches. A 1/4 inch would be .040 of that circumference or 14 degrees. We’d
have to have the exact dimensions of the notch and diameter to properly
figure this.

This EGR thing. It’s only purpose is to introduce inert exhaust into the
cylinder and this keeps the combustion temperature low enough to keep NOx
emissions low. Our Jags do not have and EGR as you well know. An old
independent Jag mechanic told me that the reason Jag does not have the EGR
is because it instead overlaps the cams to allow some exhaust to remain in
the cylinder. And this is the reason the idle is lumpy. He said to move
both cams and the idle would be much improved. This was about 8 years ago I
heard this. Since then I have asked around about this, even here on Jag
lovers, and the only answer was no it would not help but no they had not
tried it. So I tried it last spring but am unsure of the results. You can
imagine my excitement when I read your posting bout doing almost the same
thing :slight_smile:

What I should now do is make that exhaust pressure measurement, then move
the intake cam back to factory and move the exhaust cam more advanced,
measure again the exhaust pressure, change the ignition timing back to 17
degrees. And make a compression check. Maybe I’ll do this Friday. BTW I
have tried plug gap to .040 but no better idle. I’ll let you know.

Regards - Tom

----- Original Message -----
From: Chris K <@Makoto_Kino>
To: tom graham tgraham@mindspring.com
Sent: Wednesday, September 12, 2001 4:11 PM
Subject: Re: [xj] Re: rough idle timing

Hi Tom,
Well, I too started with a good engine. Replaced my valve guides, valves
and re-ground them. I only intend on using this head until I can re-build
another engine to MINT condition for a proper swap.

I have tested most systems (not ALL of them, though I am working towards
that in this project). Systems tested/verified
Fuel, Intake, Exhaust (somewhat faulty), ignition, compression, timing. I
still need to test/verify my ECU which I AM going to change, I got a lead on
a working one for dirt cheap so I figured, what the heck.

The way I see it, no car hot off the press SHOULD have a bad idle. Even a
FIAT should idle good! After all, it is a new car, and Jaguar as a matter
of fact had BETTER idle nicely, they’re co costly! After re-building a
replacement head (by hand no less), the idle was horrid, at specifications,
it stalled, shuddered and sometimes even stalled. I set out to change
anything and find what caused my junk idle.

Now, “back pressure” as I define it (and as well as my textbook) is a
suction on the exhaust pipe, that’s right, suction. If you have it, you
will know what I mean. Here’s how to test that.
Use a cloth, paper napkin, plastic bag… whatever and hold it loosely in
front of one of the mufflers, if you have back pressure, it will
occasionally suck the cloth into the muffler, it will suck it in quite hard.
No back pressure, the cloth will stay out and be blown from the muffler.
There is NO good backpressure, it’s bad. This means that a cylinder’s
exhaust valve is staying open too long and the engine is sucking in exhaust
during the intake stroke. If you have a shop scope, this should be
verifiable because the result is a huge lack of power to that cylinder and
any other that sucks in exhaust, as a matter of fact. This causes the
engine to shudder (in my case).

If you get backpressure at 60MPH, you’ve got a BIG problem, that can be
numerous things but boy I don’t think the straight 6 or any engine for that
matter can get to that speed with backpressure! If so, it would be suicidal
to the emission control system and would probably damage the engine. If
there was, back pressure at such a speed, it would in my guess be bad valve
springs.

I am waiting for my new cat to come in the mail, that will be a few days
due to this “incident”. My bad cat does not seem to be a huge problem since
at high speeds, I do not level off in power. It is bad however since it can
cause other problems.

The 20 degree cam advance was a rotation of the cam from the manufacturer
specified position (which is cam notch at 90 degrees, pointing straight up)

I only advanced the exhaust, not the intake. I was asking about that if
it is good to just advance 1 because the split overlap (time at which both
valves are open) is decreased. The exhaust valve closes sooner.

I did not choose to retard the intake because this COULD result in
backfire. That I could really do without. The engine aspiration seems to
be fine, no backfire so I left the intake cam alone. Now, from original
setting (factory), NEVER advance just the intake, this is really not
necessary in any case I can imaging and can cause immediate and massive
valve destruction. The gap between the 2 valves is quite small during
exhaust/intake. An advance in the exhaust is suitable to reduce split
overlap.
Retarding the intake and advancing the exhaust does reduce split overlap,
maybe this has somthing as well, I lowered my overlap with only the exhaust
cam
It sounds like the advance and retard was around 5 degrees per cam in your
case a total of 10 degrees to the exhaust can only would probably yield the
same result, but this is un-verified by myself.

You have a very interesting case there, do you know your compression? I’m
rather curious. Mine was about 180 as I recall, I will check again and
record later. Some people have compression at around 150, 160, etc. This
may have something to do with the end result.

EGRs… Heh I had that on a FORD escort a long time ago… I have nothing
to say for those things except “added stuff”.

Thanks for in info on the split overlap shift, I’ll see if I can find any
information on the use of such a method. Maybe one day when I have the
energy I will try removing those came overs again…arrrrgh…

Chris
Black 85 XJ6 “Michi Korosu”

Hello Chaps,
Chirs and Manfred -

Please help me understand what is going on here. Getting my Jag (any Jag?)
to idle smoothly is the “Holy Grail” for Jag lovers.

  1. What is your exhaust back pressure with the bad CAT??

  2. What is the “normal” exhaust back pressure?? Has anyone measured it at
    idle and at maybe 60mph??

  3. The 20 degree exhaust cam advance, how did you “measure” 20 degrees?

  4. Did the 20 degree exhaust advance help the idle, or was it something
    else, maybe the???

  5. Is it only your exhaust cam that is changed, ie, your intake cam is set
    at “the notch”???

  6. I have ADVANCED my exhaust cam and RETARDED the intake cam. (84S3) How
    many degrees, I don’t know, can only say that they are both off by 1/2 the
    width of the cam setting notch. That is probably 3/32 inches at the notch
    referenced to the proper 90 degree notch setting.

  7. The theory I was told is that this reduces the cams overlap, this
    reduces
    the amount of exhaust gas left in the cylinder, this results in smoother
    idle. If you have every played with an EGR valve you have seen this
    effect, that is why an EGR is vacuum controlled so it is closed at idle.

  8. So you ask, "Well Tom, is your idle better with this change??) Yes, but
    still not baby smooth. It idles at 600 rpm per its tach. AND is smooth
    only with the idle mixture screw (on the AFM) turned fully down.
    Torque/acceleration seems the same as before. But please note, I did this
    when I re-did the head gasket and the vlves were ground. So, there are too
    many variables that may be at work to clearly show cause and effect. I
    ALSO
    advanced the ignition timing to by 4 degrees to 21 BTDC. I think I’ll move
    it back to 17 and see what the idle does.

  9. Inquiring minds want to know :slight_smile: Pull me a warm Guinness please.
    Cherio - Tom

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===================================================
The archives and FAQ will answer many queries on the XJ series…
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12

I had the same sort of problem. About 2 months after I purchased my Jag, cylinder #4 started to hiss, this turned into a whistle after another month. It was rather funny, the sound was almost exactly like a turbo-charger winding up! I was dog slow but it sure sounded neat. I couldn’t agree more however, spark plugs are easy to check and those are usually the first indicators of a bad cylinder.

Chris
Black 85 XJ6 “Michi Korosu”-----Original Message-----
From: "Mark Strickland"mark@legendz.com
To: xj@jag-lovers.org
Date: Thu Sep 13 09:21:21 PDT 2001
Subject: Re: [xj] Re: rough idle timing

I’m not sure if this will help, but… I have been chasing a rough idle
on our Ford Explorer for quite a while. I decided to take to emissions to
get an idea of what was going on. I found my %co was low (idle and load),
but my HC at idle was 1420 (104 under load).

I then double/tipple checked wires and plugs (I did change the gap from 56
down to 50… I used 56 instead of the recommended 50-54 to keep pinging
down) and still had the issue. While poking around I noticed it sounded
like there was an exhaust leak. After replacing the exhaust manifold and
checking for any other leaks I decided to check for a leak in the motor. I
did a compression check and found the #6 cylinder (back cylinder on our v6)
only had 60psi in it while the rest had 160-170psi (not bad for 246k
miles). This is after I took it to other shops to figure out what was
going on and they were blaming wires, wrong plugs, over gapping plugs, bad
sensors, bad TPS, MAS etc…

so, what I’m getting at is don’t forget the basics… Need Gas, Air, Spark,
and compression to work… (I forgot about compression… $300 in parts
later I remembered and checked it)

Looks like I need to finish putting in that rear end in our '73 SI xj6 so I
can take the motor on the explorer apart and rebuild it…

Good Luck, and Good Hunting

~Mark

Mark
mark@legendz.com
http://mark.legendz.com
Off-Road and Motorcycle Information, Pictures and Movies

===================================================
The archives and FAQ will answer many queries on the XJ series…
FAQs: http://www.jag-lovers.org/xjlovers/xjfaq/index.html
Archives: Jag-lovers Forums - Jag-lovers

To remove yourself from this list, go to Jag-lovers Forums - Jag-lovers.

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Get Your Free, Private E-mail at http://mail.go.com

===================================================
The archives and FAQ will answer many queries on the XJ series…
FAQs: http://www.jag-lovers.org/xjlovers/xjfaq/index.html
Archives: Jag-lovers Forums - Jag-lovers

To remove yourself from this list, go to Jag-lovers Forums - Jag-lovers.

13

I had the same sort of problem. About 2 months after I purchased my Jag, cylinder #4 started to hiss, this turned into a whistle after another month. It was rather funny, the sound was almost exactly like a turbo-charger winding up! I was dog slow but it sure sounded neat. I couldn’t agree more however, spark plugs are easy to check and those are usually the first indicators of a bad cylinder.

Chris
Black 85 XJ6 “Michi Korosu”-----Original Message-----
From: "Mark Strickland"mark@legendz.com
To: xj@jag-lovers.org
Date: Thu Sep 13 09:21:21 PDT 2001
Subject: Re: [xj] Re: rough idle timing

I’m not sure if this will help, but… I have been chasing a rough idle
on our Ford Explorer for quite a while. I decided to take to emissions to
get an idea of what was going on. I found my %co was low (idle and load),
but my HC at idle was 1420 (104 under load).

I then double/tipple checked wires and plugs (I did change the gap from 56
down to 50… I used 56 instead of the recommended 50-54 to keep pinging
down) and still had the issue. While poking around I noticed it sounded
like there was an exhaust leak. After replacing the exhaust manifold and
checking for any other leaks I decided to check for a leak in the motor. I
did a compression check and found the #6 cylinder (back cylinder on our v6)
only had 60psi in it while the rest had 160-170psi (not bad for 246k
miles). This is after I took it to other shops to figure out what was
going on and they were blaming wires, wrong plugs, over gapping plugs, bad
sensors, bad TPS, MAS etc…

so, what I’m getting at is don’t forget the basics… Need Gas, Air, Spark,
and compression to work… (I forgot about compression… $300 in parts
later I remembered and checked it)

Looks like I need to finish putting in that rear end in our '73 SI xj6 so I
can take the motor on the explorer apart and rebuild it…

Good Luck, and Good Hunting

~Mark

Mark
mark@legendz.com
http://mark.legendz.com
Off-Road and Motorcycle Information, Pictures and Movies

===================================================
The archives and FAQ will answer many queries on the XJ series…
FAQs: http://www.jag-lovers.org/xjlovers/xjfaq/index.html
Archives: Jag-lovers Forums - Jag-lovers

To remove yourself from this list, go to Jag-lovers Forums - Jag-lovers.

GO.com Mail
Get Your Free, Private E-mail at http://mail.go.com

===================================================
The archives and FAQ will answer many queries on the XJ series…
FAQs: http://www.jag-lovers.org/xjlovers/xjfaq/index.html
Archives: Jag-lovers Forums - Jag-lovers

To remove yourself from this list, go to Jag-lovers Forums - Jag-lovers.