[xj] Series 3 Lack of power under load?

XJ
1

Hi Everyone,

Weirdly of all the many Jags I’ve had (S1 XJ6’s, S2 XJ12, XJS, E-type, Mk
X) I’ve never really spent alot of time with a S3 XJ6 so I’m not all that
positive about what is normal. Now that I’ve gotten this 85 and have
sorted all the brake issues and electrical stuff, I’ve been driving it
around pretty hard to shake any further gremlins loose before I drive it
to South FL in a few weeks.

Here’s the thing: The car runs pretty nicely in general. Idles well, seems
to have decent power while cruising, etc… The one thing I’ve noticed is
that it seems a little weak when I drive up the mountain I live on. It’s
not a huge mountain (about 1800 ft) and not super steep but when I put the
spurs to my S1 it drops into second and has no problem flying up the hill
at 70. If I just keep the S1 in 3rd it still seems alot more eager to go
up the hill than the S3.

When I get to a slightly steep area and push the accelerator on the S3 it
drops into second but doesn’t give me the rush of acceleration that the S1
does… just sort of slowly meanders a little faster. Does this sound
normal to you S3 guys?

Am I nuts or am I just spoiled because my silver S1 is a beast :slight_smile: ?
That car has no pollution devices and no mechanical fan to suck the power
but it does still have a BW12 tranny and no fancy fuel injection.

I havent’ really started digging into stuff like timing and compression
readings etc… just wondering if I’m chasing a non-existent demon.

Thanks,
~Mike
72 XJ6
73 XJ6
85 XJ6–
RustfreeMike
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–

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2

No, it isn’t normal, and I would suspect possibly the catalytic converters
being clogged if the timing etc are not the problem.

Gregory
Victoria, Canada-----Original Message-----
From: RustfreeMike
Sent: Friday, March 25, 2016 10:04 AM
To: xj@jag-lovers.org
Subject: [xj] Series 3 Lack of power under load?

Hi Everyone,

Here’s the thing: The car runs pretty nicely in general. Idles well, seems
to have decent power while cruising, etc… The one thing I’ve noticed is
that it seems a little weak when I drive up the mountain I live on. It’s
not a huge mountain (about 1800 ft) and not super steep but when I put the
spurs to my S1 it drops into second and has no problem flying up the hill
at 70. If I just keep the S1 in 3rd it still seems alot more eager to go
up the hill than the S3.

When I get to a slightly steep area and push the accelerator on the S3 it
drops into second but doesn’t give me the rush of acceleration that the S1
does… just sort of slowly meanders a little faster.

===================================================
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3

Hi Everyone,

Weirdly of all the many Jags I’ve had (S1 XJ6’s, S2 XJ12, XJS, E-type, Mk
X) I’ve never really spent alot of time with a S3 XJ6 so I’m not all that
positive about what is normal. Now that I’ve gotten this 85 and have
sorted all the brake issues and electrical stuff, I’ve been driving it
around pretty hard to shake any further gremlins loose before I drive it
to South FL in a few weeks.

Here’s the thing: The car runs pretty nicely in general. Idles well, seems
to have decent power while cruising, etc… The one thing I’ve noticed is
that it seems a little weak when I drive up the mountain I live on. It’s
not a huge mountain (about 1800 ft) and not super steep but when I put the
spurs to my S1 it drops into second and has no problem flying up the hill
at 70. If I just keep the S1 in 3rd it still seems alot more eager to go
up the hill than the S3.

When I get to a slightly steep area and push the accelerator on the S3 it
drops into second but doesn’t give me the rush of acceleration that the S1
does… just sort of slowly meanders a little faster. Does this sound
normal to you S3 guys?

Agree with Gregory, Mike - it ain’t ‘normal’; you may need to start start
digging…:slight_smile:

However, while the two transmissions have virtually the same ratios; do the
two cars have the same rear axle ratio?
Engine power is all about rpms - and a fair test involves comparing rpms in
the situations described at the shift down point. And, of course; rpm
build-up is closely related to rear axle ratio - not omitting to mention
that the SI is some 500 pounds lighter…

Emission restrictions does interfere with engine power, as does the
mechanical fan - it all adds up, but still…:slight_smile:

Frank
xj6 85 Sov Europe (UK/NZ)

Am I nuts or am I just spoiled because my silver S1 is a beast :slight_smile: ?
That car has no pollution devices and no mechanical fan to suck the power
but it does still have a BW12 tranny and no fancy fuel injection.

I havent’ really started digging into stuff like timing and compression
readings etc… just wondering if I’m chasing a non-existent demon.-----Original Message-----
From: RustfreeMike
Sent: Saturday, March 26, 2016 6:04 AM
To: xj@jag-lovers.org
Subject: [xj] Series 3 Lack of power under load?

===================================================
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4

In reply to a message from Frank sent Sat 26 Mar 2016:

I suspect that the S3 has the 2.88 axle ratio
and that the S1 has a lower one, 3.54 or
so.

Comparing tach readings at the same
mph’s would be a clue.

And, no question, as Frank says,
500 pounds does deter the alacrity
of the 85!!!

As the BW’s lacked an OD, Jaguar
sought to make do with the 2.88 ratio.

And, could it be that the S1 has a higher
compression ratio and therefore, more
‘‘grunt’’. One point can be felt in
the seat of the pants.

Carl–
The original message included these comments:

Here’s the thing: The car runs pretty nicely in general. Idles well, seems
to have decent power while cruising, etc… The one thing I’ve noticed is
that it seems a little weak when I drive up the mountain I live on. It’s
not a huge mountain (about 1800 ft) and not super steep but when I put the
spurs to my S1 it drops into second and has no problem flying up the hill
at 70. If I just keep the S1 in 3rd it still seems alot more eager to go
up the hill than the S3.

–
Carl Hutchins 1983 Jaguar XJ6 with LT1 and 1994 Jeep Grand
Walnut Creek, California, United States
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
–Support Jag-lovers - Donate at http://www.jag-lovers.org/donate04.php –

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5

Mike,

I encountered the same symptoms  with my 1984 XJ6 VdP shortly after

getting it. The catalytic converter was badly clogged and restricting
airflow through the engine. There was a huge difference driving the car
after a new catalytic converter was installed.

Regards,

Paul M. Novak

1990 Series III V12 Vanden Plas
1990 XJ-S Classic Collection convertible
1987 XJ6 Vanden Plas
1984 XJ6 Vanden Plas
1969 E-Type FHC
1957 MK VIII Saloon
Ramona, CA
P.M.Novak7@gmail.com-----Original Message-----
From: owner-xj@jag-lovers.org [mailto:owner-xj@jag-lovers.org] On Behalf Of
RustfreeMike
Sent: Friday, March 25, 2016 10:05 AM
To: xj@jag-lovers.org
Subject: [xj] Series 3 Lack of power under load?

Hi Everyone,

Weirdly of all the many Jags I’ve had (S1 XJ6’s, S2 XJ12, XJS, E-type, Mk
X) I’ve never really spent alot of time with a S3 XJ6 so I’m not all that
positive about what is normal. Now that I’ve gotten this 85 and have sorted
all the brake issues and electrical stuff, I’ve been driving it around
pretty hard to shake any further gremlins loose before I drive it to South
FL in a few weeks.

Here’s the thing: The car runs pretty nicely in general. Idles well, seems
to have decent power while cruising, etc… The one thing I’ve noticed is
that it seems a little weak when I drive up the mountain I live on. It’s not
a huge mountain (about 1800 ft) and not super steep but when I put the spurs
to my S1 it drops into second and has no problem flying up the hill at 70.
If I just keep the S1 in 3rd it still seems alot more eager to go up the
hill than the S3.

When I get to a slightly steep area and push the accelerator on the S3 it
drops into second but doesn’t give me the rush of acceleration that the S1
does… just sort of slowly meanders a little faster. Does this sound normal
to you S3 guys?

Am I nuts or am I just spoiled because my silver S1 is a beast :slight_smile: ?
That car has no pollution devices and no mechanical fan to suck the power
but it does still have a BW12 tranny and no fancy fuel injection.

I havent’ really started digging into stuff like timing and compression
readings etc… just wondering if I’m chasing a non-existent demon.

Thanks,
~Mike
72 XJ6
73 XJ6
85 XJ6

–
RustfreeMike

===================================================
The archives and FAQ will answer many queries on the XJ series…
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6

In reply to a message from Dr. Gregory Andrachuk sent Fri 25 Mar 2016:

Thanks for the input everyone! Today I’m gonna do a back-pressure
test of the exhaust system as well as check the timing etc… On the
one hand I hope it does wind up being a slightly clogged cat but on
the other hand those things are pretty expensive. With my luck it
won’t be a muffler :slight_smile:

They don’t emission test where I live so I may wind up fabricating
some new pipes if that turns out to be the issue.

Will let you know what I find.

Best,
~Mike
72 XJ6
73 XJ6
85 XJ6–
The original message included these comments:

No, it isn’t normal, and I would suspect possibly the catalytic converters
being clogged if the timing etc are not the problem.
Gregory

–
RustfreeMike
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
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7

In reply to a message from Frank sent Sat 26 Mar 2016:

Okay Gentleman - I have the results of my back pressure test. I’m
assuming that the exhaust in a US spec Series 3 is pretty
restrictive with 2 Cats and 2 resonators… but the results seem to
show more restriction than I think there should be. Not terrible but
maybe getting toward clogged territory. What do you think?

Procedure - hooked my old-faithful vacuum/pressure gauge to the open
end of the AIR injection manifold. The only thing good about that
AIR injection system is that it makes it easy to get a back-pressure
reading. Car at operating temp. Gauge jumps around alot before about
2500 RPM so tough to get a good reading but it is low.

IDLE - 0 PSI
2000 RPM - approximately .25 (or less) PSI
3000 RPM - 1.25 PSI
3500 RPM - 1.5 PSI
3800 RPM - 2 PSI

Going back in the garage to look at the timing.

~Mike–
The original message included these comments:

Agree with Gregory, Mike - it ain’t ‘normal’; you may need to start start
digging…:slight_smile:
However, while the two transmissions have virtually the same ratios; do the
two cars have the same rear axle ratio?
Engine power is all about rpms - and a fair test involves comparing rpms in
the situations described at the shift down point. And, of course; rpm
build-up is closely related to rear axle ratio - not omitting to mention
that the SI is some 500 pounds lighter…
Emission restrictions does interfere with engine power, as does the
mechanical fan - it all adds up, but still…:slight_smile:
Frank

–
RustfreeMike
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
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8

In reply to a message from RustfreeMike sent Sat 26 Mar 2016:

Hi enviable Rustfree,

I was going to comment that my Series 1 seems faster as it
loses weight via rusting out of the sills–but that’s not
your problem. :slight_smile:

But I had a problem a while back that listers thought might
be exhaust restriction. I did some tests based on vacuum
readings at speed and immediately after releasing the
throttle. That might be something else to try…I can’t
interpret your direct back pressure readings. Crudely, I
finally resolved that back pressure wasn’t the problem by
cutting a big chunk out of the downpipe to see if anything
changed…it did not, and I felt pretty stupid for having
done it.–
The original message included these comments:

show more restriction than I think there should be. Not terrible but
maybe getting toward clogged territory. What do you think?

–
Bob Wilkinson, 73 XJ6
Saint Louis, MO, United States
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
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9

Mike,

a pre-emission control SI should put out around 180 hp, while a
non-catalyst SIII will put out 205 hp. US versions may lack some 10 %
(that was the typical loss of power from non-catalyst to catalyst
engines we encountered from 1986-88 when cats weren’t yet compulsory in
Germany and car makers offered both versions in parallel). If your SI is
SWB, odds are that your SIII weighs some 200 kg more. So, it may well be
that your SI out-performs the SIII in hillclimbing.

Yet, the difference should be marginal, if both cars have auto boxes.
So, from what you describe I’d be afraid that maybe the torque converter
or poorly adjusted breaking bands are eating up even more oomph than
they typically do.

Clogged converters might be the cause, as Dr. Gregory suggested. In my
limited experience the power lack is limited to high speed cruising,
making the converters work like a speed limiter. How about your car? The
easiest way to check power is a full-speed run - if the car makes in
excess of 4800 RPM on a flat road that’s as good as it gets and no
problem with the engine. Of course, this requires adequate “testing
facilities” …

Good luck

Jochen

1975 XJ6L 4.2 auto (UK spec)> Date: Fri, 25 Mar 2016 10:04:41 -0700

From: "RustfreeMike"goatwith1000young@gmail.com
Subject: [xj] Series 3 Lack of power under load?

Hi Everyone,

Here’s the thing: The car runs pretty nicely in general. Idles well, seems
to have decent power while cruising, etc… The one thing I’ve noticed is
that it seems a little weak when I drive up the mountain I live on. It’s
not a huge mountain (about 1800 ft) and not super steep but when I put the
spurs to my S1 it drops into second and has no problem flying up the hill
at 70. If I just keep the S1 in 3rd it still seems alot more eager to go
up the hill than the S3.

When I get to a slightly steep area and push the accelerator on the S3 it
drops into second but doesn’t give me the rush of acceleration that the S1
does… just sort of slowly meanders a little faster. Does this sound
normal to you S3 guys?

Am I nuts or am I just spoiled because my silver S1 is a beast :slight_smile: ?
That car has no pollution devices and no mechanical fan to suck the power
but it does still have a BW12 tranny and no fancy fuel injection.

I havent’ really started digging into stuff like timing and compression
readings etc… just wondering if I’m chasing a non-existent demon.

Thanks,
~Mike
72 XJ6
73 XJ6
85 XJ6

===================================================
The archives and FAQ will answer many queries on the XJ series…
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10

In reply to a message from RustfreeMike sent Sat 26 Mar 2016:

Mike,

If they don’t do an emissions test where you live, get rid
of the catalytic converters ASAP. Don’t even fool around
with the back pressure test.

I had a Series I with a Series III engine which had no
catalytic converters. Even with the USA Stromberg
carburetors that car was a VERY spirited driving machine.
You will be amazed at the difference, seriously!!!

Just don’t forget to disclose the absence of the cats to any
buyer that may live where they do test.–
The original message included these comments:

They don’t emission test where I live so I may wind up fabricating
some new pipes if that turns out to be the issue.
Will let you know what I find.

–
Gordon S. Tompkins (2009 XK Coupe’)
Oakdale, CA, United States
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
–Support Jag-lovers - Donate at http://www.jag-lovers.org/donate04.php –

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11

In reply to a message from Robert Wilkinson sent Sat 26 Mar 2016:

Hi Bob - Sadly my rustfree moniker doesn’t extend to the Fast
Silver Series 1… it too has sills that are mostly rust and bondo

  • so yeah, power to weight ratio is probably better because of it
    :slight_smile:

Checked the timing and if anything it’s actually about 1 degree
advanced from where it should be - no pinking or knocking however
so that ain’t it. Also vacuum advance capsule functions as it
should.

So I just drove it down the mountain to pick up pizza and then back
up again. Definitely a little wimpy up the mountain. The
transmission isn’t slipping but I get the impression that there’s
alot of power being sucked up by it. Possibly failing torque
converter as Jochen said. Also I used up alot of gas trying to get
it moving… Seems like the engine is doing what it’s supposed to
and the tranny is letting it down. One of the first things I did
when I got the car was change the tranny fluid and filter because I
know that the old man who had it actually drove it around for a
short time with the brakes completely locked up! Fluid was pretty
bad but no sign of major damage. No big particles or anything.
Think I’m gonna change it again however and have a look at the band
adjustment. I have the original receipts for the car and for some
reason it had 2 transmission replacements under warranty in the
80’s…

Gordon, I don’t live in an emissions state so I probably will
switch out the exhaust to get rid of the cats at some point. I
think 2 PSI back pressure at 3800 rpm may be within spec but it
certainly ain’t good. A car with a really efficient system should
be less than 1 PSI all the time.

Really interested to hear what Frank thinks of the back-pressure
readings.

Thanks again everyone!

~Mike–
The original message included these comments:

I was going to comment that my Series 1 seems faster as it
loses weight via rusting out of the sills–but that’s not
your problem. :slight_smile:
But I had a problem a while back that listers thought might
be exhaust restriction. I did some tests based on vacuum
readings at speed and immediately after releasing the
throttle. That might be something else to try…I can’t

–
RustfreeMike
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
–Support Jag-lovers - Donate at http://www.jag-lovers.org/donate04.php –

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12

Mike,

I have never done a test like you have done, so I have no idea if those

numbers make sense or not. However, when I had clogged catalytic
converters and replaced them myself, I tested both the old cat after I
removed it, and the new one before I installed it side by side, with my
Sears shop vacuum cleaner on blow. I connected the hose of my shop vacuum
to one side of the cat and held it in place with duct tape, then I turned it
on. With a new cat there was no noticeable change in the sound of the
vacuum motor and the air blew easily through the matrix with little or no
back pressure. The story with the clogged cats was much different as you
could hear the vacuum motor straining to push the air through and the
pressure of the air coming out the other end of the clogged cat was
noticeably less. Of course I was already committed to removing the old cats
because I pretty much knew that they were clogged and once I removed them I
could see that they were clogged. However, the vacuum test was a nice
confirmation that the clogged cats were definitely affecting air flow
through the engine. Once I replaced the cats there was a very noticeable
improvement in performance.

I live in CA and the four newer Jaguars require smog tests every two
years. So I need to keep those cars running properly and appropriately
configured to make sure that they pass the visual and emissions gas tests.

Regards,

Paul M. Novak

1990 Series III V12 Vanden Plas
1990 XJ-S Classic Collection convertible
1987 XJ6 Vanden Plas
1984 XJ6 Vanden Plas
1969 E-Type FHC
1957 MK VIII Saloon
Ramona, CA
P.M.Novak7@gmail.com-----Original Message-----
From: owner-xj@jag-lovers.org [mailto:owner-xj@jag-lovers.org] On Behalf Of
RustfreeMike
Sent: Saturday, March 26, 2016 12:52 PM
To: xj@jag-lovers.org
Subject: Re: [xj] Series 3 Lack of power under load?

In reply to a message from Frank sent Sat 26 Mar 2016:

Okay Gentleman - I have the results of my back pressure test. I’m assuming
that the exhaust in a US spec Series 3 is pretty restrictive with 2 Cats and
2 resonators… but the results seem to show more restriction than I think
there should be. Not terrible but maybe getting toward clogged territory.
What do you think?

Procedure - hooked my old-faithful vacuum/pressure gauge to the open end of
the AIR injection manifold. The only thing good about that AIR injection
system is that it makes it easy to get a back-pressure reading. Car at
operating temp. Gauge jumps around alot before about
2500 RPM so tough to get a good reading but it is low.

IDLE - 0 PSI
2000 RPM - approximately .25 (or less) PSI
3000 RPM - 1.25 PSI
3500 RPM - 1.5 PSI
3800 RPM - 2 PSI

Going back in the garage to look at the timing.

~Mike

–
The original message included these comments:

Agree with Gregory, Mike - it ain’t ‘normal’; you may need to start
start
digging…:slight_smile:
However, while the two transmissions have virtually the same ratios;
do the two cars have the same rear axle ratio?
Engine power is all about rpms - and a fair test involves comparing
rpms in the situations described at the shift down point. And, of
course; rpm build-up is closely related to rear axle ratio - not
omitting to mention that the SI is some 500 pounds lighter…
Emission restrictions does interfere with engine power, as does the
mechanical fan - it all adds up, but still…:slight_smile: Frank

–
RustfreeMike

===================================================
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FAQs: http://www.jag-lovers.org/xjlovers/xjfaq/index.html
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13

In reply to a message from Paul M. Novak sent Sat 26 Mar 2016:

Hi Paul,

Ha! Now that’s the kind of low-tech test I can get behind - Shop
vac on blow! Nice.

I think there’s definitely some restriction going on with mine -
not terrible but it certainly ain’t helping. 2 PSI isn’t great.
I’ve seen cars with plugged cats that couldn’t go over 25 mph…
so it could be worse.

I’m sure at some point I’ll switch over to no-cats but for now I
think I’ll have to live with them.

Best,
~Mike–
The original message included these comments:

I have never done a test like you have done, so I have no idea if those

numbers make sense or not. However, when I had clogged catalytic
converters and replaced them myself, I tested both the old cat after I
removed it, and the new one before I installed it side by side, with my
Sears shop vacuum cleaner on blow. I connected the hose of my shop vacuum
to one side of the cat and held it in place with duct tape, then I turned it
on. With a new cat there was no noticeable change in the sound of the
vacuum motor and the air blew easily through the matrix with little or no
back pressure. The story with the clogged cats was much different as you
could hear the vacuum motor straining to push the air through and the
pressure of the air coming out the other end of the clogged cat was

–
RustfreeMike
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
–Support Jag-lovers - Donate at http://www.jag-lovers.org/donate04.php –

===================================================
The archives and FAQ will answer many queries on the XJ series…
FAQs: http://www.jag-lovers.org/xjlovers/xjfaq/index.html
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14

In reply to a message from Frank sent Sat 26 Mar 2016:

Okay Gentleman - I have the results of my back pressure test. I’m
assuming that the exhaust in a US spec Series 3 is pretty
restrictive with 2 Cats and 2 resonators… but the results seem to
show more restriction than I think there should be. Not terrible but
maybe getting toward clogged territory. What do you think?

Back pressure tests are iffy, Mike it’s a fairly wide range of ‘OK’…

I think you should also check manifold vacuum response - as a back-up.
Nominally one would expect 18" Hg in idle - expressing normal engine power.
Clogging exhaust would lower readings - as will a lot of other things. To
test for clogging; rev to 3000 rpms and watch the vacuum, with pedal
steady - if vacuum gradually drops it signifies exhaust clogging. Nominally
at 3000 rpms, unloaded, vacuum should still be around 18"…

As for the gearbox; slipping should be noticeable - at downshift the rpms
should rise about 500 rpms. and of course, while accelerating in ‘2’; rpms
should only rise gradually with speed.

Frank
xj6 85 Sov Europe (UK/NZ)

Procedure - hooked my old-faithful vacuum/pressure gauge to the open
end of the AIR injection manifold. The only thing good about that
AIR injection system is that it makes it easy to get a back-pressure
reading. Car at operating temp. Gauge jumps around alot before about
2500 RPM so tough to get a good reading but it is low.-----Original Message-----
From: RustfreeMike
Sent: Sunday, March 27, 2016 8:52 AM
To: xj@jag-lovers.org
Subject: Re: [xj] Series 3 Lack of power under load?

===================================================
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15

In reply to a message from Frank sent Sun 27 Mar 2016:

Bob:

Let’s see, does FE + O weigh more
than sound FE?

In Mike’s case, add the
weight of Bondo?

Mike:

If indeed, the torque converter
is going out, slippage would
increase. More RPM and less MPH!!!

If I recall correctly, there are two
plugs on the manifold. Purpose?
If I ever knew, I’ve forgotten.

Remove them to relieve back pressure.
Lots of noise, but don’t let that
lead you astray, ‘‘noise isn’t power’’.

Jut compare the RPM’s and MPH’s on
that Pizza hill. Open vs closed?

Way back when I was a kid, Billy
loosened the exhaust donut nuts
on his 40 Chev ex-USGS car. Much more
like his straight out of the manifold
T.

Later, I did the same to get
my anemic 34 Chevrolet to sound healthier
and less like a vacuum cleaner.
Black Tudor, red wires, sans front fenders
and hood/bonnet, looked good!

Olden mufflers were very restrictive.

Modern cats far less so.

Carl–
The original message included these comments:

Clogging exhaust would lower readings - as will a lot of other things. To
test for clogging; rev to 3000 rpms and watch the vacuum, with pedal
steady - if vacuum gradually drops it signifies exhaust clogging. Nominally
at 3000 rpms, unloaded, vacuum should still be around 18’'…
As for the gearbox; slipping should be noticeable - at downshift the rpms
should rise about 500 rpms. and of course, while accelerating in ‘2’; rpms
should only rise gradually with speed.

–
Carl Hutchins 1983 Jaguar XJ6 with LT1 and 1994 Jeep Grand
Walnut Creek, California, United States
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
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16

In reply to a message from RustfreeMike sent Fri 25 Mar 2016:

In another direction, just check the ignition timing. It may not
have enough advance. That will show the same symptoms. I have had
a similar experience with my Series 3, and I have no idea why it
happened, other than a particularly bad backfire, caused by
another problem.–
The original message included these comments:

Weirdly of all the many Jags I’ve had (S1 XJ6’s, S2 XJ12, XJS, E-type, Mk
X) I’ve never really spent alot of time with a S3 XJ6 so I’m not all that
positive about what is normal. Now that I’ve gotten this 85 and have
Here’s the thing: The car runs pretty nicely in general. Idles well, seems
to have decent power while cruising, etc… The one thing I’ve noticed is
not a huge mountain (about 1800 ft) and not super steep but when I put the
spurs to my S1 it drops into second and has no problem flying up the hill
up the hill than the S3.

–
nifty 1
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17

In reply to a message from RustfreeMike sent Sat 26 Mar 2016:

You may wish to conduct a ‘‘stall test’’ which takes 5 minutes
and is designed to test torque convertor function…dont
know if the data is in S3 manual?

I would also want to know for sure my relative diff ratios,
afaic acceleration/power to the road is directly
proportional to diff ratios.

quite likely is cat as you suspect, but one other thing to
check is brake binding, caused by old hoses, look for
excessive wheel heat/smell–
The original message included these comments:

So I just drove it down the mountain to pick up pizza and then back
up again. Definitely a little wimpy up the mountain. The
transmission isn’t slipping but I get the impression that there’s
alot of power being sucked up by it. Possibly failing torque
converter as Jochen said. Also I used up alot of gas trying to get
it moving… Seems like the engine is doing what it’s supposed to

–
Tony
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18

In reply to a message from awg sent Mon 28 Mar 2016:

Hi guys - sorry for the delay in answering. Thanks again to
everyone for the input.

Tony - stall speed test is gonna happen today. The more I drive
it the more I feel there may be a tranny issue. Brakes are all
good cause when I bought the car a month ago they were locked
solid. All calipers and rubber lines are new.

Nifty had mentioned timing - timing is good, plugs and wires are
new NGK’s new rotor as well. Vaccuum advance is also working
fine - holds a vaccuum and moves easy.

I do have what may be a fuel pump issue - going to start a new
thread about that.

Best,
~Mike
72 XJ6
73 XJ6
85 XJ6–
The original message included these comments:

You may wish to conduct a ‘‘stall test’’ which takes 5 minutes
and is designed to test torque convertor function…dont
know if the data is in S3 manual?
I would also want to know for sure my relative diff ratios,
afaic acceleration/power to the road is directly
proportional to diff ratios.
quite likely is cat as you suspect, but one other thing to
check is brake binding, caused by old hoses, look for
excessive wheel heat/smell

–
RustfreeMike
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
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19

In reply to a message from Frank sent Sun 27 Mar 2016:

Hi again everyone,

I just got back from a 50 mile drive that took me down the
mountain and of course back up, some highway driving and some slow
moving around-town stuff. The car performed admirably except for
the general feeling of sluggishness that’s been plaguing me.
Checked the stall speed of the tranny and it’s at 1900 by the
car’s tach after that long run. The book says 1950-2100.

I still need to put the vacuum gauge on it as Frank suggested but
beyond that I had another thought as follows:

The car idles a bit high - 900 RPM when warm. There is no sign
that the idle was ever messed with because the plug is still on
the AFM (not definitive I know). Also I have 30 years of receipts
that I’ve gone through and I can’t find any mention of it being
adjusted. This is just thinking out loud but is it possible that
the AAV is not closing all the way causing my high warm idle and
my general ball-lessness? I can’t find any other evidence of an
air leak even after spraying around all duct connections with WD.

This Jag’s got the ‘Grace’ and ‘Space’ but it is definitely
lacking in the ‘Pace’ department.

~Mike
72 XJ6
73 XJ6
85 XJ6–
The original message included these comments:

Back pressure tests are iffy, Mike it’s a fairly wide range of ‘OK’…
I think you should also check manifold vacuum response - as a back-up.
Nominally one would expect 18’’ Hg in idle - expressing normal engine power.
Clogging exhaust would lower readings - as will a lot of other things. To
test for clogging; rev to 3000 rpms and watch the vacuum, with pedal
steady - if vacuum gradually drops it signifies exhaust clogging. Nominally
at 3000 rpms, unloaded, vacuum should still be around 18’'…
As for the gearbox; slipping should be noticeable - at downshift the rpms
should rise about 500 rpms. and of course, while accelerating in ‘2’; rpms
should only rise gradually with speed.

–
RustfreeMike
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
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20

In reply to a message from Frank sent Sun 27 Mar 2016:

Hi again everyone,

I just got back from a 50 mile drive that took me down the
mountain and of course back up, some highway driving and some slow
moving around-town stuff. The car performed admirably except for
the general feeling of sluggishness that’s been plaguing me.
Checked the stall speed of the tranny and it’s at 1900 by the
car’s tach after that long run. The book says 1950-2100.

Being slightly ‘off spec’ likely means the engine is not at desired power,
Mike - rather than a gearbox fault…

The idle rpms is is adjusted by the idle screw at the air distribution block
(5,5 mm hex). The screw at the AFM (5 mm hex) is the AFM bypass - which is
used to regulate fuel mixture. The AFM flap deflection regulates the amount
of fuel injected by measuring the amount of air entering the engine - and
the bypass slightly vary the deflection by passing more or less air past the
flap.

The bypass is initially factory set to ‘tune’ the AFM to the ECU - it can be
readjusted, compensating for AFM ‘drift’ normally using CO as a marker. In
theory; your mixture may now be incorrect and you can adjust it by altering
the bypass. Counting the turns, bottom the screw - this was the original
setting, to be remembered, around 4 turns is ‘normal’. Then try different
settings from the original set - however, the screw has limited effects on
fuelling, and only checking with a CO sniffer will reveal any fuelling
anomalies causing engine power loss…

The adjustments will not change the idle - which must be set by the idle
screw. However, the idle has no influence on engine power - but manifold
vacuum will reveal something about engine power…

Frank
xj6 85 Sov Europe (UK/NZ)

I still need to put the vacuum gauge on it as Frank suggested but
beyond that I had another thought as follows:

The car idles a bit high - 900 RPM when warm. There is no sign
that the idle was ever messed with because the plug is still on
the AFM (not definitive I know). Also I have 30 years of receipts
that I’ve gone through and I can’t find any mention of it being
adjusted. This is just thinking out loud but is it possible that
the AAV is not closing all the way causing my high warm idle and
my general ball-lessness? I can’t find any other evidence of an
air leak even after spraying around all duct connections with WD.

This Jag’s got the ‘Grace’ and ‘Space’ but it is definitely
lacking in the ‘Pace’ department.-----Original Message-----
From: RustfreeMike
Sent: Sunday, April 03, 2016 8:19 AM
To: xj@jag-lovers.org
Subject: Re: [xj] Series 3 Lack of power under load?

===================================================
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

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