[xj40] 1990 Xj40 Rough Idle and funny cylinder operation

XJ40
1

Well I am new here, first post. This place is a wealth of
information and I hope to bring my own experience to the table as
well as find more info. I have had this car for a few years now and
have done lots of work to it. New shocks, struts, brakes (including
the ABS pump), new steering rack, tie rod ends, control arm
bushings, wheel bearings,fixed fuel tank leak, and various other
fixes and preventative maintenence.

Well that was my short intro now my current issue…

My car was running fine but I had intermitent power issues that
were mostly resolved with the replacement of the TPS, coolant temp
sensor, and O2 sensor. I still get some funny power issues when it
is very cold ~32 degrees F. I had a lean running contion due to the
above parts.

One day I was comming up a very steep hill on the highway and all
of a sudden I felt a fairly severe loss of power. It was work to
keep it at 75 mph. At home I noticed it idles very rough,
especially when in gear–the car would shudder.

Removal of each spark plug wire revealed that the number 5 cylinder
was not firing well at all. The engine rpm would hardly change for
that cylinder. I figured I had a burned valve due to weakness
caused by previous lean condition and the heat caused from climbing
the hill.

I did a compression test and found interesting results. All
cylinders had great compression 140-150 range but the number 5 was
down in the 120 psi range. I took it to a shop I have access to and
did a leak down test while also checking valve lifter clearances.
All lifter clearneces were within spec although a few on other
cyls. were a very tiny bit over. A second compression test said
that the #5 cylinder had perfect compression but it even jumped up
to 300 PSi at one test.

The leak down did not produce any great findings. At high pressures
up to 180 pounds no leaking could be heard from the throttle body
or from the exhaust pipes. However it sounded like a leak into the
crank case somewhere as you could hear air flowing in through the
oil fill port and in the front of the engine. The air flowing
through the crankcase slowed to almost nothing when it got down to
80 -100 pounds and all cylinders held air fine and leaked only
slowly. The air flowing through what I can tell is the crankcase
happened on all 6 of the cyls. so I assume that is normal.

It began to run a bit better but still rough idle and kind of doggy
at around 50 Mph but will run much better at higher rpms. So I am
thinking I have a broken valve spring or worn guide. Which may
explain the intermitent good compression numbers.

Sorry for the book wanted to be as clear as I could. Just hoping
someone else might have some insight as to why I have this running
condition before I take the plunge and pull the head. I should also
note that I have good fuel pressure and spark. No vacume leaks that
I can find.

Thanks–
GunnerMan
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2

In reply to a message from GunnerMan sent Wed 28 Dec 2011:

Welcome to the forum.

Sorry to see no one has come up with any brilliant
suggestions about what the cause(s) of the problem you are
experiencing may be.
With those cylinder compression figures (if conducted on a
warm engine with WOT) seemingly eliminating a problem with
valves and your ‘leak-down’ test appearing normal, I think
in your position I would be looking for something more
mundane being the cause of loss of power.

How old are the plug leads? I’ve known them break down under
load and I guess 75 mph up a steep hill falls in to that
category.

I wouldn’t have thought it is a valve spring problem -
otherwise you should see an increase in valve clearance on
the one with a broken spring.–
The original message included these comments:

My car was running fine but I had intermitent power issues that
One day I was comming up a very steep hill on the highway and all
of a sudden I felt a fairly severe loss of power. It was work to
keep it at 75 mph. At home I noticed it idles very rough,
especially when in gear–the car would shudder.
Removal of each spark plug wire revealed that the number 5 cylinder
was not firing well at all. The engine rpm would hardly change for

–
Bryan N, '91 Sovereign 4.0 L, RHD
Cambridgeshire, United Kingdom
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
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3

In reply to a message from Bryan N sent Thu 29 Dec 2011:

Today I started to think along the same lines. I was looking for
something to spend my evening with so I went to the shop and
started to tinker with the car. I found that the cylinder that I
thought was not firing well had a spark plug that was white as
could be, I also diconnected power to it’s injector and noticed a
loss of power telling me the cylinder is working. Other plugs
looked just the same. This indicates a lean running condition.

I also took off the exhaust manifold as I had this impulse to do
so. I inspected the first cats comming from the engine and they
were very clean. The whole exhaust system seemed very clean and in
overall good condition.

I did find that I am weeping oil around the back corner area of the
head on the exhaust side. I also have the infamous oil weep from
the front corner near the distributor as well. No signs of burning
oil though.

The battery was disconnected and I found that that car does run
somewhat better. This has happened before and it usually only lasts
a few days.

I also have started to hear the alternator squeal for a second when
there is heavy load IE headlights, heater/ac, radio on at the same
time. The belts are tight and are not a year old and still very
clean looking. When I was idling in gear today I saw that the power
supplied to the headlights and fuel pump was directly tied to
engine rpm. The engine would stumble a bit and cause the lights to
dim a bit and the pump to slow down a bit. It seems the alternator
is always working. O’Reilly said my battery was in good shape a few
months ago when it was tested.

It almost sounds like it might be an idle air control valve
problem. The IAC screw must be almost completely closed in order
for the car to idle at the propper range.

Plug leads are old. I need new ones but there is good spark to
every plug.

Tomorrow my list of things to go over is check the CPS clearance
and possition, clear computer once more and reset idle, check for
air leaks/vaccume leaks once more, test the alternator/battery.

I should also note that there is this sound at idle you can hear
when outside of the car. It sounds almost like a diesel engine but
very muted; the kind of gurgle and plink sound that sounds like it
is comming from the front portion of the crank case but I can not
tell for sure. I started the car with the manifold off for a second
but it was deafening and I could not hear anything. The exhaust
comming out was clear as air.

Thanks or the reply. Really would like to get to the bottom of
this. I hate driving a Jag around that sounds like it’s drowning
and shakes at the stop lights like it has some low quality low
rider package.–
GunnerMan
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4

In reply to a message from GunnerMan sent Fri 30 Dec 2011:

Are your plugs whiter than these?

http://www.jag-lovers.org/snaps/snap_view.php3?id=1240953873

Surely if it is running that badly due to a weak mixture you
should get a VCM code - do you get a CEL?

As to your charging / battery problem, have you checked the
rubber bonded crankshaft pulley/damper in case it has
sheared and is slipping under load, perhaps causing the
‘squeal’ on start-up?

Who is O’Reilly? :-)–
The original message included these comments:

started to tinker with the car. I found that the cylinder that I
thought was not firing well had a spark plug that was white as
I also have started to hear the alternator squeal for a second when
there is heavy load IE headlights, heater/ac, radio on at the same
time. The belts are tight and are not a year old and still very

–
Bryan N, '91 Sovereign 4.0 L, RHD
Cambridgeshire, United Kingdom
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
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5

In reply to a message from Bryan N sent Fri 30 Dec 2011:

Yes, the plugs are whiter. They more closely resemble the plugs
shown in the Haynes book for lean plug condition. I was going to
take a photo but forgot.

I do have a CEL it is FuelFail 39 (EGR fault). I have been fighting
the egr for a year. First it was a bad valve; shortly after that
fix the solenoid went out. I am not sure what other stuff could be
broken with it besides the temperature sensor. If I clear the CEL
the car runs much better until it finds the fault again. I am
assuming it finds the fault and just uses default values in the ECU
causing poor and erratic performance.

Right now my plan is to replace the head gasket because I am sick
of the oil and it gives me a chance to inspect valve condition.
While I have it apart replace the egr valve gaskets, ensure it is
all clean, and test the sensor. I can not detect any leaks from the
system.

After some reading I have decided that my alternator is wearing
out. Can’t find the exact info but it was explained that one of the
stators in the alternator can wear or go bad. This still enables
the alternator to work but can no longer supply maximum output.–
GunnerMan
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