[xj40] Engine Dies When Coasting to a Stop

XJ40
1

Hello, all,

My 1991 Sovereign starts and runs fine for about 45 minutes and
then the engine cuts out while coasting to a stop. It will start
up again but the engine will run rough with a lumpy/faster idle.
There are no VCM codes. If I park and let it cool down, the same
thing occurs. The problem appears to be temperature-related as
everything is good when starting from cold and the problem
consistently begins after about 45 minutes of driving.

Recent repairs include: new fuel pump and replacement evaporative
flange (used but with good electrical connectors), new CPS, new EGR
valve and EGR solenoid, new ignition amp, new coil and HT leads,
and new CTS. When I replaced the CTS,the insulation on the CTS
wires from the harness was very brittle. I replaced the connector
and wires up to the point where the leads enter the harness. I
wonder if there might be more bad insulation inside the fuel
injection harness.

Any suggestions of other things to check would be much appreciated.
The owner of the repair shop where my Jag has resided for these
past many months and I are quite perplexed. I did search for clues
in the archives.

Aloha from Honolulu,
Leland–
Leland, '91 Sovereign
Honolulu/Hawaii, United States
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2

In reply to a message from Leland sent Sat 10 Nov 2012:

Leland

Do you still have the old HT leads ? - if so try putting them back
in and see if the problem is still there
Personally dont believe that its anything in yr Ignition Harness as
if that was the case then it would probably be there all the time -
the cables from the harness (where they come out of the harness
itself) on mine certainly all do get brittle and cook hard - if
they then get moved the outer insulation tends to crack off and
bare wires then appear
I generally repair by cutting and then insert heat shrink cable
wrapping before soldering the wires back together - the heat shrink
then slides over the solder and then gets shrunk onto the
connection - seems to work on mine.

If the HT leads dont sort out the problem then get back to the
forum and sure someone wil have some other ideas (I assume that you
have eliminated the fuel tank from the problem - it is 'breathing ?

Best luck

Nigel–
1987 XJ40 3.6 Auto Sov SAJJHALH3AA512874
Singapore, Singapore
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3

In reply to a message from Nigel Snowden sent Sat 10 Nov 2012:

In the old days of manual fuel pumps - a dying pump would
leave you stranded at a stop light.

I am wondering if you are getting fuel starvation when you
reach the stop?

Does the car idle when you first start the car?–
The original message included these comments:

have eliminated the fuel tank from the problem - it is 'breathing ?

–
John 90 XJ40
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4

In reply to a message from John S sent Tue 13 Nov 2012:

Hi, John and Nigel,

Thank you for your replies. As far as we can tell, all is normal
with the fuel tank. We had the tank in and out a few times (and
replaced the fuel pump) until we discovered a burned contact in the
evaporative flange. Prior to this, the car died, could not be
started again, and had to be towed. After we replaced the flange,
we started experiencing the current problem. This time, when the
engine dies, it will restart, though it doesn’t run smoothly. The
funny thing is that for the first 45 minutes or so, everything runs
just fine, including the idle.

I’ll try replacing the wire from the coil to the distributor cap,
per Nigel’s suggestion. If the problem was one of the plug wires,
wouldn’t the engine start missing rather than quitting altogether?

BTW, I didn’t mention earlier that my car has about 148k miles on
it.

Aloha and thanks,
Leland–
Leland, '91 Sovereign
Honolulu/Hawaii, United States
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5

In reply to a message from Leland sent Tue 13 Nov 2012:

You might check the air temperature sensor and possibly the water
temperature sensor (not sender) that feed the ECU. Also clean the
MAF while you’re there. These sensors are cheap and with 148k on
the odometer changing them would not hurt.

I once had a slowly deteriorating MAF meter on my XJ40 that caused
the car to stall when going slow around corners. Eventually a code
showed up.

Gary–
The original message included these comments:

engine dies, it will restart, though it doesn’t run smoothly. The
funny thing is that for the first 45 minutes or so, everything runs
just fine, including the idle.

–
Gary K '92 XJS Convertible 5.3 '94 XJ40 '97 X300 VDP
Greenville, SC, United States
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6

In reply to a message from Leland sent Tue 13 Nov 2012:

Leland

It is not unheard of that the HT leads can fail/undeperform when
hot (its a difficult fault to detect as when cool they appear to
perform perfectly well) - this could cause some of the problems you
appear to be having.

You say will run after restart but is ‘lumpy’ - this could be
indication that one of the HT leads is failing.

I would recommend that if you stil have all the old leads (and they
were working well beforehand) then replace ALL of them again and
see if the porblem is still there - if it now performs ok then its
a question of elimination to find which one of the new ones is
causing the problem.
If the porblem is still there then you have eliminated one possible
cause.

Similar operation with the coil if the porblem does not disappear
when the HT leads are replaced

Check and clean the connections to the ignition amplifier as well -
anything in that areas tends to get very warm !

When you coast to stop then the air circulation in that area
virtually stops and temperatures will tend to climb locally very
quickly

Best Luck

Nigel–
1987 XJ40 3.6 Auto Sov SAJJHALH3AA512874
Singapore, Singapore
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7

In reply to a message from Nigel Snowden sent Tue 13 Nov 2012:

Aloha, all,

Thanks much for the great ideas for things to check. I don’t have
my old set of plug wires so I’ll need to figure out how to check
this, hopefully without having to buy another new set.

I just talked to someone today who parted out a '91 VDP to ask if
he still has the MAF. He said he thought so and would check. His
car only had 52k miles when it was totalled so his used parts are
good condition.

If we do the MAF, I will also replace the bellows between the
intake elbow and the throttle body; and do a thorough cleaning of
the throttle body and EGR port. My mechanic suspects that the
bellows may be cracked and creating an air leak.

I’ll let you know how things go after we get this all done.

Thanks, again.

Best regards,
Leland–
Leland, '91 Sovereign
Honolulu/Hawaii, United States
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8

In reply to a message from Leland sent Thu 15 Nov 2012:

Aloha, all,

Just a bit of an update. Cleaned out the throttle body and egr port
(which was totally clogged); and replaced the torn bellows in the
air intake. The car ran perfectly for almost an hour and then the
engine died while slowing to a stop, same as before. This time, the
vcm showed a FF 29 – failed ecu self-check. My mechanic is in the
process of cleaning the blue and yellow ecu connectors and
replacing the ems/ecu relay. We’ll take it on the road again and
see how it goes. The forum says that ecu failures are rare; but if
we wanted to change it out, is an exact part number replacement
necessary? Mine is a DBC 6332 but I have seen a DBC 6352 available
on eBay.

Any comments or suggestions would be appreciated.

Best regards,
Leland–
Leland, '91 Sovereign
Honolulu/Hawaii, United States
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9

In reply to a message from Leland sent Thu 20 Dec 2012:

Does the engine sort of taper off and stumble or just shut
off abruptly? Does it only happen when you take your foot
off the pedal? Will it pick back up if you give it more gas?–
The original message included these comments:

Just a bit of an update. Cleaned out the throttle body and egr port
(which was totally clogged); and replaced the torn bellows in the
air intake. The car ran perfectly for almost an hour and then the
engine died while slowing to a stop, same as before. This time, the
vcm showed a FF 29 – failed ecu self-check. My mechanic is in the
process of cleaning the blue and yellow ecu connectors and
replacing the ems/ecu relay. We’ll take it on the road again and
see how it goes. The forum says that ecu failures are rare; but if

–
Pete Peterson 70E(193K) 88XJ40s(270K & 256K) 94XJ40 (122K)
Severna Park, Maryland, United States
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10

In reply to a message from Leland sent Thu 20 Dec 2012:

Leland,

It does sound as though there is a problem in the ECM circuits.

Here are items to check from the diagnostic flowchart for
stalling:

Low fuel pressure, ignition faults

Transmission fluid level low (or possibly overfilled)

ECM electrical connections wet or corroded (check for A/C
drains clogged with deteriorated foam from around the
evaporator coil and dash vents))

Is ECM connector fully engaged?

Clean ECM grounds - test with ohmmeter - inspect ECM ground
at intake manifold stud - are eyelets installed between
bracket and nut with serrated washer under the nut? If not,
correct.

Orientation of ignition module wires - if pointed in same
direction as coil high tension tower, reorient 90 degrees.

Clean ignition coil tower and primary terminals - are pins
backed out of ignition module connector?

Faulty king lead from coil to distributor?

Inspect oxygen sensor connections - are connectors and boots
fully engaged?

Is oxygen sensor operating properly? If not, check for fuel
metering or air intake leak problems or oxygen sensor problem.

Is base idle set correctly to 700 rpm +/- 50 rpm for AT, 800
rpm +/-5- rpm for manual.

I hope this info may help. Please let us know what you
discover.

Don–
The original message included these comments:

Just a bit of an update. Cleaned out the throttle body and egr port
(which was totally clogged); and replaced the torn bellows in the
air intake. The car ran perfectly for almost an hour and then the
engine died while slowing to a stop, same as before. This time, the
vcm showed a FF 29 – failed ecu self-check. My mechanic is in the
process of cleaning the blue and yellow ecu connectors and
replacing the ems/ecu relay. We’ll take it on the road again and
see how it goes. The forum says that ecu failures are rare; but if
we wanted to change it out, is an exact part number replacement
necessary? Mine is a DBC 6332 but I have seen a DBC 6352 available
on eBay.

–
Don B : '93 VDP Flamenco Red 187K : (ex-'88 Sovereign)
Franklin, TN, United States
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11

In reply to a message from Don B sent Fri 21 Dec 2012:

Thanks, very much, Don and Pete, for your replies. Sorry for the
delay in responding – Christmas holiday fun kind of took over.
Well, changing the ecu relay and cleaning the connectors did not
solve the problem. Some of the items you mentioned were addressed
recently, such as the coil, plug and coil wires, and ignition
amplifier, which were all replaced. We will swap out the ecu with a
used replacement and see what happens. Does anyone know if a DBC
6332 ecu is interchangeable with a DBC 6352? And I will print out
and share your comments with my mechanic, as well.

Have a very Happy New Year!

Aloha,
Leland–
Leland, '91 Sovereign
Honolulu/Hawaii, United States
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12

In reply to a message from Leland sent Thu 27 Dec 2012:

Leland,

Don’t forget to check your transmission fluid level. It
seems counterintuitive, but that is the first check on the
Jaguar diagnostics chart for engine stalling. I can only
assume that low transmission fluid (or possibly overfilled
fluid) may somehow affect torque converter behavior so that
the engine encounters unintended drivetrain resistance and
stalls.

I can’t answer your ECU question - hopefully someone else
can. If those part numbers are for different model year
cars, the ECUs may be mapped for different fuel injectors,
electronic vs. mechanical transmission, etc., so they may
not be interchangeable. Let us know what you figure out.

Don–
The original message included these comments:

Thanks, very much, Don and Pete, for your replies. Sorry for the
delay in responding – Christmas holiday fun kind of took over.
Well, changing the ecu relay and cleaning the connectors did not
solve the problem. Some of the items you mentioned were addressed
recently, such as the coil, plug and coil wires, and ignition
amplifier, which were all replaced. We will swap out the ecu with a
used replacement and see what happens. Does anyone know if a DBC
6332 ecu is interchangeable with a DBC 6352? And I will print out
and share your comments with my mechanic, as well.
Have a very Happy New Year!

–
Don B : '93 VDP Flamenco Red 187K : (ex-'88 Sovereign)
Franklin, TN, United States
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13

In reply to a message from Don B sent Thu 3 Jan 2013:

Leland,
This happened on my car a few years back. There was oil in
the rheostat winding of the throttle position sensor. I
dropped it off the throttle body. drilled a 1/8’’ hole in the
center of the bottom and cleaned it out with throttle body
cleaner. It lasted long enough for me to get a new one off the
internet and have time to change it.
R,
Gunner–
Gunner 94 VDP 221K+ miles Kingfisher Blue
Hendersonville/Tn, United States
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