[modern] Stalling after engine warm-up

Disused Categories Modern
1

I’ve got a 1988 Sovereign with the 3.6L engine. Ever since I’ve owned it,
I’ve had trouble with intermittent stalling and rough running.
Here are the symptoms:

  1. Never stalls from a cold start.
  2. After running for 15-20 minutes, it usually begins to run roughly -
    though sporadically when it does begin to run rough.
  3. Particularly kicks into “rough running/stall mode” upon turning a corner
    or a change in speed, i.e. letting off the gas pedal and braking.
  4. But, sometimes it will go all day without running rough or stalling.

Here’s what I’ve done so far:

  1. Changed plugs
  2. Replaced distributor cap and rotor.
  3. Cleaned out fuel tank (clean as a whistle, which makes me mad as I did it
    for nothing…).
  4. Replaced fuel filter
  5. Replaced throttle potentiometer (though I metered it and it checked good,
    my problem is intermittent so…)
  6. Replaced fuel pressure regulator
  7. Metered MAF and it checks good
  8. Idle speed is correct

I know that Jaguar issued a tech service bulletin in the early 90’s for
“Stalling in Turns” or something to that effect, but I can’t get my hands on
it. Every service center I come across wants to replace the ECU - but I
don’t like that idea, and don’t think it will fix the problem based on the
symptoms.
Any help would be greatly appreciated.

Oland
1988 Sovereign, 1991 XJS V12

2

Oland,

I’ve got a 1988 Sovereign with the 3.6L engine. Ever since I’ve owned it,
I’ve had trouble with intermittent stalling and rough running.
Here are the symptoms:

  1. Never stalls from a cold start.

On a cold start, the ECU is not looking at the oxy sensor…

  1. After running for 15-20 minutes, it usually begins to run roughly -

After the engine is warmed up, some extra things start happening…
ECU in closed loop,
EGR system enabled(if equipped, your car does not have it)
Evap system sucks fumes out of vapor recovery system…big vacuum
leak could cause problem…

though sporadically when it does begin to run rough.
3. Particularly kicks into “rough running/stall mode” upon
turning a corner
or a change in speed, i.e. letting off the gas pedal and braking.

Maybe a connection that is disturbed by the engine moving in its
mounts…more likely, water in climate control system getting into
ECU.

  1. But, sometimes it will go all day without running rough or stalling.

Here’s what I’ve done so far:

  1. Changed plugs
    What type/brand?
  1. Replaced distributor cap and rotor.
  2. Cleaned out fuel tank (clean as a whistle, which makes me mad
    as I did it
    for nothing…).
  3. Replaced fuel filter
  1. Replaced throttle potentiometer (though I metered it and it
    checked good,
    my problem is intermittent so…)
    A good idea…
  1. Replaced fuel pressure regulator
  2. Metered MAF and it checks good

What does it measure at hot idle, and at full throttle?
How did the connections look?

  1. Idle speed is correct
    How did you set this(and the tps)

I know that Jaguar issued a tech service bulletin in the early 90’s for
“Stalling in Turns” or something to that effect, but I can’t get
my hands on
it. Every service center I come across wants to replace the ECU - but I
don’t like that idea, and don’t think it will fix the problem based on the
symptoms.
Very unlikely to be an ECU fault…

Any help would be greatly appreciated.

Oland
1988 Sovereign, 1991 XJS V12

Here are some things to check…
Coil…look for signs of tracking on the ht tower.
Make sure the plug wires are not resting on anything, or contacting
the engine…check the wires around the ignition amp and coil, as well
as the actual ignition amp connector.
The low voltage wires should not be near the high voltage
coil wire.

Transmission fluid level…low fluid can stall engine!

Inspect ECU connections for moisture.

Check the ground connections at the intake manifold stud.

Check the coolant temp sensor hot and cold…
Cold reading should be about 5900 ohms at 32F(0C) and 250 ohms
at 193F(90C).

You can also measure the vacuum reading on a hot engine at idle.
At sea level, it should be around 19 inches…

The base idle speed, and tps settings are quite important
in how the engine reacts to varying loads…
The base idle speed is supposed to be about 600 rpm, and the iscv
is supposed to be able to increase or decrease it from there, to
compensate for various loads on the engine from the power steering system,
the alt, and the ac compressor, as well as changes in engine temps…

Have you ever tried just turning the steering wheel at the approximate time
the engine would stall, but without moving?

Its possible, if the base idle speed is off, or the iscv
(Idle Speed Control Valve)is not working correctly, that the extra
load on the engine would be enough to stall it.

I would also suspect a vacuum leak…maybe in the vapor recovery
system. There is a big vacuum line off the bottom of
the intake manifold that runs to the recovery tank in the left side
spoiler…there is also a smaller vacuum control line that runs down there,
and all sorts of valves and hoses that can be rusted up or split.

Brett
1990 XJ6

3

Oland,

the one thing you haven’t mentioned is the CPS, which may be going bad. Not
sure if it fits the going round corners story though, but it’s a cheaper
components which is known to fail and as a major input to the ECU can cause
all sorts of problems including a dead stop.

Cheers - Jez> -----Original Message-----

From: Whitecotton Oland T TSgt 627AMSS/SE
[mailto:Oland.Whitecotton@mildenhall.af.mil]
Sent: 20 February 2001 14:03
To: ‘modern@jag-lovers.org’
Subject: [modern] Stalling after engine warm-up
Importance: Low

I’ve got a 1988 Sovereign with the 3.6L engine. Ever since
I’ve owned it,
I’ve had trouble with intermittent stalling and rough running.
Here are the symptoms:

  1. Never stalls from a cold start.
  2. After running for 15-20 minutes, it usually begins to run roughly -
    though sporadically when it does begin to run rough.
  3. Particularly kicks into “rough running/stall mode” upon
    turning a corner
    or a change in speed, i.e. letting off the gas pedal and braking.
  4. But, sometimes it will go all day without running rough or
    stalling.

Here’s what I’ve done so far:

  1. Changed plugs
  2. Replaced distributor cap and rotor.
  3. Cleaned out fuel tank (clean as a whistle, which makes me
    mad as I did it
    for nothing…).
  4. Replaced fuel filter
  5. Replaced throttle potentiometer (though I metered it and
    it checked good,
    my problem is intermittent so…)
  6. Replaced fuel pressure regulator
  7. Metered MAF and it checks good
  8. Idle speed is correct

I know that Jaguar issued a tech service bulletin in the
early 90’s for
“Stalling in Turns” or something to that effect, but I can’t
get my hands on
it. Every service center I come across wants to replace the
ECU - but I
don’t like that idea, and don’t think it will fix the problem
based on the
symptoms.
Any help would be greatly appreciated.

Oland
1988 Sovereign, 1991 XJS V12

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4

Oland,
Brett’s advise is, as usual, ‘on the nose’. When checking the terminals of
the engine management ECU, make sure that no water has actually entered the
unit.

I don’t know how the ECU’s for 4.0L engines are constructed. I do know that
those on my 2.9L could have water in them. It was sloshing about and
contacting the electronic components, even though the multipin plug and
sockets were pristine and had absolutely no sign of water or moisture at
those locations.

Kind Regards,
John Tarrant.