[v12-engine] Cold start problem

V12-Engine
1

Dear friends,

My 86 V12 HE suddenly developed a cold starting issue and I
am a bit at a loss here.
Have been troubleshooting for a week with no result.

She will fire and idle very roughly.
The idle will hunt between 200 and 500 rpm, and after about
15 sec, or as soon as I touch the gas pedal, she dies…
After the 19th or so consecutive attempt she will fire and
all is fine, will restart with no problem and engine idles
and runs flawlessly.
Next morning the same story all over again…

Noticed that an injector hose would leak just by touching
it, so I replaced all engine fuel hoses.
I took the opportunity to change the injector seals and the
same time rerouted some cables.

Coolant Temp Sensor reads 2.6 K ohms @ 10�C
Placed a 4.2 K ohms resistance and there was a mild improvement.
When disconnected the idle improves even more but still hunts.

Air Temp Sensor reads 3.3 K ohms @ 10�C
FPR is not leaking.
I think the Ignition is doing it’s job, all 12 pistons
ignite, and all 12 injectors click.
Auxiliary Air Valve works and have extra boost from the
Supplementary Air Valve through a switch.

There is some popping at the intakes.
I disconnected the FPR vacuum line, no improvement.
Fiddled with the ECU’s idle fuel mixture, no improvement.

After the 19th or so attempt it will progressively get
better but it’s the 20th or so attempt that will make the
difference, she will fire and all is forgotten.
It worked enough for the temperature to rise and cure the
problem?

I know, I also need a fuel Pressure gauge, but I don’t have
one, and we are in the country here.

Have pre-pump fuel filters, pump is slightly noisy but
nothing extreme.
When I disconnect the fuel line and run the pump there is
plenty of fuel coming out.
When I block the hose the pump slows down to zero.

As if I am low in fuel pressure though, and therefore the
hunting idle, but combined with injectors that don’t stay
open long enough, and can’t explain why.
And yet again it can run as good as it does after it climbs
that step.

What am I missing ?

Thank you all.
Aristides–
Aristides Balanos, 1986 XJ V12,VDP - www.e-psychi.com/jaguar
Roussillon, Provence, France
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2

I had exactly the same problem. My cure turned out to be the wiring
from the Coolant Temp Sensor. It was really frustrating to find and
it wasn’t really cured until I changed the connector. I installed a
used BMW injector connector. It has an excellent design.

The idle hunt is a different problem and won’t be able to be solved
until the CTS problem is cured.

Ptipon
Sonora/CA, 90 XJS-V12 conv, United StatesOn Jan 23, 2016, at 8:08 AM, Aristides wrote:

Coolant Temp Sensor reads 2.6 K ohms @ 10°C
Placed a 4.2 K ohms resistance and there was a mild improvement.
When disconnected the idle improves even more but still hunts.

Thank you all.
Aristides

Aristides Balanos, 1986 XJ V12,VDP - www.e-psychi.com/jaguar
Roussillon, Provence, France

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3

My 86 V12 HE suddenly developed a cold starting issue and I
am a bit at a loss here.
Have been troubleshooting for a week with no result.

She will fire and idle very roughly.
The idle will hunt between 200 and 500 rpm, and after about
15 sec, or as soon as I touch the gas pedal, she dies…
After the 19th or so consecutive attempt she will fire and
all is fine, will restart with no problem and engine idles
and runs flawlessly.
Next morning the same story all over again…

Aristides

Roussillon, Provence, France------------------------------------------------------------------------------------------------------

200 to 500 RPM suggests:
a) Not enough air.
b) Or not enough fuel, or maybe just too much fuel.
c) Or maybe firing on less than 12 cylinders.

a) You opened the throttle and it dies, so lack of air not a problem.
However, if there is a microswitch that also activates when you open
the throttle, lack of air could be a problem that is masked.
You say the AAV is o.k. If there is a microswitch can you open the
throttle but inhibit the microswitch ?

b) When all is well the fuelling is determined by the ECU computing
from a combination of RPM and manifold vacuum.
With a cold engine fuelling will be increased by the signal from the
coolant sensor.
You say by disconnecting the coolant sensor the idle improves but still hunts.
Does that mean the RPM increases ? By how much ?

The ECU fuel map has cells, and as RPM or vacuum changes and the
operating point moves to another cell the engine should stabilise at
that new point.
If there is hunting then there is an unexpected change so the engine
cannot operate in the new cell.
That means an input to the ECU has changed too much or too little, so
the engine returns to the old cell and hunts.
Is the ECU getting the correct vacuum and RPM signals ?
The other influence is timing advance which changes with RPM. If that
gives unexpected change you can have hunting.

Below 500RPM is not usually a valid operating region so hunting is
more likely at the best of times.

c) it is possible the ignition is suspect when cold, although usually
it gives more trouble when hot.
Sticking dizzy advance is a slight possibilty to cause trouble, but
probably not in this case.
I guess you have overhauled the dizzy in the last 5 years.

If you get good results only after 19 starts I doubt anything has
warmed up much on the engine.
One good thing is that the problem and cure sound very consistent.

With ignition on the CEI ignition unit and ECU will self warm.
You could turn the ignition on and sit for 15 minutes to let them warm
up then start the engine and see what happens.

You could put an electric fan heater under a cold engine and run that
for an hour.
See if that helps starting.

If heating up various things does not help, maybe it is vibration related.
Eventually something gets shaken up and starts working.
Vibration related problems and cures are not usually very consistent.

Richard Dowling, Melbourne, Australia. 1979 coupe + HE V12 + manual;
1989 convertible; 2003 XJ350.

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4

In reply to a message from Paul Tipon sent Sat 23 Jan 2016:

Paul,

Yes, the CTS would be a prime suspect.
My connector and contacts though are in pretty good shape.
Any idea how could I troubleshoot it’s wiring ?
With the sensor disconnected, and ignition on, one pin has
~2.5V and the other ~0.2V. Does that mean something?

Aristides–
The original message included these comments:

I had exactly the same problem. My cure turned out to be the wiring
from the Coolant Temp Sensor. It was really frustrating to find and
it wasn’t really cured until I changed the connector. I installed a
used BMW injector connector. It has an excellent design.

–
Aristides Balanos, 1986 XJ V12,VDP - www.e-psychi.com/jaguar
Roussillon, Provence, France
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5

In reply to a message from Richard Dowling sent Sat 23 Jan 2016:

Thank you for your input Richard.

a) Can’t open the throttle not even slightly, the engine
dies instantly.
When I press the micro switch it makes no difference.

b) The engine can work fine, so vacuum connection to ECU
must be OK.
When I disconnect the coolant sensor the idle increases to
500rpm, but it’s still not a healthy idle, it hunts and
still dies.

Now, RPM signal, that is an interesting thought.
How does one check that?
The tachometer works fine, no jerks or inconsistencies.

As the engine can work and respond very well the vacuum
advance must also work as it should, no?

c)well, in every start the engine idles badly from 5 to
30sec before it dies. So there is some time to warm things up.
Also sometimes will she will restart right away and some
other times she needs quit a lot of cranking.

I will try out your suggestions about the ECU and report
back. A cold solder inside that suddenly makes contact?
Wish I had a spare one…

Aristides–
The original message included these comments:

a) You opened the throttle and it dies, so lack of air not a problem.
However, if there is a microswitch that also activates when you open
the throttle, lack of air could be a problem that is masked.
You say the AAV is o.k. If there is a microswitch can you open the
throttle but inhibit the microswitch ?
b) When all is well the fuelling is determined by the ECU computing
from a combination of RPM and manifold vacuum.
With a cold engine fuelling will be increased by the signal from the
coolant sensor.
You say by disconnecting the coolant sensor the idle improves but still hunts.
Does that mean the RPM increases ? By how much ?

–
Aristides Balanos, 1986 XJ V12,VDP - www.e-psychi.com/jaguar
Roussillon, Provence, France
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6

With the sensor disconnected, and ignition on, one pin has
~2.5V and the other ~0.2V. Does that mean something?

That ain’t right, is it? I thought one end should read 5V. Anybody know for
sure?

For your sake, I hope it’s not a bad ECU.

– Kirbert

Visit the Jag Lovers homepage at http://www.jag-lovers.org for exciting services and resources including Photo Albums, Event Diary / Calendar, On Line Books and more !On 23 Jan 2016 at 22:57, Aristides wrote:

7

In reply to a message from Kirbert sent Sat 23 Jan 2016:

Hi Kirbert,

Measured again, and I was wrong… too much confusion yesterday.

One reads 6.5v but the other reads also 6.5v and gradually
falls to about 2.5v.

Any thoughts ?

Aristides–
The original message included these comments:

That ain’t right, is it? I thought one end should read 5V. Anybody know for
sure?
For your sake, I hope it’s not a bad ECU.

–
Aristides Balanos, 1986 XJ V12,VDP - www.e-psychi.com/jaguar
Roussillon, Provence, France
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8

One reads 6.5v but the other reads also 6.5v and gradually
falls to about 2.5v.

Any thoughts ?

Yeah. Sounds like a bad ECU. I hope I’m wrong.

– Kirbert

Visit the Jag Lovers homepage at http://www.jag-lovers.org for exciting services and resources including Photo Albums, Event Diary / Calendar, On Line Books and more !On 23 Jan 2016 at 23:49, Aristides wrote:

9

Measured again, and I was wrong… too much confusion yesterday.

One reads 6.5v but the other reads also 6.5v and gradually
falls to about 2.5v.

Any thoughts ?

Aristides--------------------------------------------------------
Not conclusive, the ECU will supply a voltage suitable to measure
current ( hence resistance ) in the CTS.
Depending on the circuit design, could be a variety of voltages and
also with no CTS connected it could float and give different results
with different multimeters.

To be sure connect a resistor, say 1K ( but anything from 100ohm to 5K
should work ), across the 2 terminals and measure the voltage at both
ends of resistor with respect to ground.
Then somebody ( me ? ) can put the same resistor across terminals and
see if the same voltage is seen.

If the problem is in the ECU remember it appears to work perfectly
after a while.
That could be due to self heating, that thing will draw current and
heat up even when the engine is stopped and ignition on.
It will heat up a bit more when the injector circuits are firing.

You could try heating the ECU before you start the engine, see if that
makes a difference.

However, recall that an open circuit in the CTS caused the engine to
increase idle to 500RPM.
That suggests the ECU responds to CTS input.

My convertible is an 89 Lucas, I guess almost the same as your 86 car.
In 7 years of ownership never had need to pry into the engine
management, so not 100% familiar with it.
I would think that your ECU is probably o.k., but it hunts because
either the RPM or vacuum signal is not correct.

The tacho is driven by a signal from the ignition circuit.
I have looked at the XJ-S HE repair manual .pdf file, and it mentions
all manner of things about the engine management.
There is no mention about the RPM signal to the ECU.
Later cars have a sensor on the flywheel for RPM, maybe for Lucas
systems they use the tacho signal.
The ECU must have some RPM signal that is almost correct or the engine
just will not work.
That signal may be noisy or have the wrong amplitude, wrong waveform
when RPM increases with a cold engine.
Suddenly it comes right. Amazing !

There may be a vacuum switch on your car that is supposed to operates
at low RPM and high load ( low vacuum ) to give 12% enrichment.
If that is faulty it could cause hunting too.

I would still try heating the engine bay, or heating the ECU to
eliminate one or the other.

Richard Dowling, Melbourne, Australia. 1979 coupe + HE V12 + manual;
1989 convertible; 2003 XJ350.

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10

In reply to a message from Kirbert sent Sun 24 Jan 2016:

Before you mess with the ECU, confirm the basics – air,
fuel, spark (not yellow, blue-ish!).

The resistance of the CTS should be 2.2.-2.5 kOhm cold and
on order of magnitude lower at operating temperature.
Verify these numbers across the CTS terminals AND at the
pins of the ECU connector.

If you confirm it is the culprit, it is cheap and very easy
to replace.

Good luck,
Steve

PS A coil/amp on its way out is more likely to not work at
times, and all of a sudden – smooth running engine–
The original message included these comments:

Yeah. Sounds like a bad ECU. I hope I’m wrong.

–
'95 XJS convertible - V12 6.0L
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11

In reply to a message from Richard Dowling sent Sun 24 Jan 2016:

Thank you all for your help and advice.

Update:
I checked thoroughly the Coolant and Air Temperature
sensors, the plugs and the wiring.
The resistant values are correct in respect of temperature,
cold and warm, and I get the same resistance readings at the
plug of the ECU in the trunk, therefore the sensors, the
plugs and the wiring are in good working order.

I restarted the engine yesterday, this time it was easier,
but more anomalies started to appear.
First the left bank started pinging every time I applied the
throttle. Some times a lot, some times a little and only the
left bank.
Probably the left bank running way to lean?
After five minutes it fixed it’s self, all back to normal again.

Next step was to plug in my Feedback Monitor so I could see
how the ECU is responding to the oxygen sensor signal.
In the beginning all appeared well but a couple of minutes
later the right bank was on full rich and stopped oscillating.
It actually had started misbehaving back in September.

After some minutes again the left bank went also on full
rich, and the ECU stopped responding in any Idle Mixture
adjustment.

I think that Kirby you are right, my ECU is giving up.

I have now the ECU in the bench trying to find obvious
faults, but no luck so far.

The question is where to go from now… 6cu or 16cu?
And there are many 16cu variants
DAC 6335
DAC 6337
DAC 6338
DAC 4585

The current one is a 6cu DAC 3586 and the car is a 1986
Canadian market.

Thanks again,
Aristides

http://www.jag-lovers.org/snaps/snap_view.php3?id=1441013783--
The original message included these comments:

If the problem is in the ECU remember it appears to work perfectly
after a while.
That could be due to self heating, that thing will draw current and
heat up even when the engine is stopped and ignition on.
It will heat up a bit more when the injector circuits are firing.

–
Aristides Balanos, 1986 XJ V12,VDP - www.e-psychi.com/jaguar
Roussillon, Provence, France
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12

I think that Kirby you are right, my ECU is giving up.

Ugh. Honestly, I know of only two reliable ways of confirming an ECU fault:

  1. Swap in a known good ECU, see if problem clears up.

  2. Ship ECU off to someone who knows how to test and service them, like
    AJ6 Engineering.

The question is where to go from now… 6cu or 16cu?

According to Bywater, the 16cu is pin-compatible – meaning it’s a plug-in
replacement for the 6cu – and is significantly better. I suspect it might also
be easier to come by.

And there are many 16cu variants
DAC 6335
DAC 6337
DAC 6338
DAC 4585

The current one is a 6cu DAC 3586 and the car is a 1986
Canadian market.

Oxygen sensors? Cats?

– Kirbert

Visit the Jag Lovers homepage at http://www.jag-lovers.org for exciting services and resources including Photo Albums, Event Diary / Calendar, On Line Books and more !On 24 Jan 2016 at 23:25, Aristides wrote:

13

In reply to a message from Kirbert sent Mon 25 Jan 2016:

Yes, it has Oxygen sensors and Cats.

David Boger has a 16cu DAC 6335 from a 1989 XJS for sale on
his site.
Would that work?
I read Bywater’s article on his site and he states that the
DAC 6335 is for Lucas ignition and cat.

Best,
Aristides–
The original message included these comments:

Oxygen sensors? Cats?

–
Aristides Balanos, 1986 XJ V12,VDP - www.e-psychi.com/jaguar
Roussillon, Provence, France
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14

In reply to a message from Aristides sent Mon 25 Jan 2016:

Aristides:
What is your original part #?
If the same, it should work. If not, it may need some
modding.

I am asking because I had an extensive email exchange with
Mr. Bywater some time ago. He told me that the 36CU fitted
in the XJS and the 1994 XJ12 are not identical, and that the
EPROM needs to be changed.
For what is worth it, they do not have the same part
numbers.

Of course, the later cars have much more electronic
components, which could be the reason swapping ECUs may not
be straightforward.

Best regards,
Steve–
The original message included these comments:

Yes, it has Oxygen sensors and Cats.
David Boger has a 16cu DAC 6335 from a 1989 XJS for sale on
his site.
Would that work?
I read Bywater’s article on his site and he states that the
DAC 6335 is for Lucas ignition and cat.

–
'95 XJS convertible - V12 6.0L
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15

Next step was to plug in my Feedback Monitor so I could see
how the ECU is responding to the oxygen sensor signal.
In the beginning all appeared well but a couple of minutes
later the right bank was on full rich and stopped oscillating.
It actually had started misbehaving back in September.
Jag-lovers Forums - Jag-lovers

After some minutes again the left bank went also on full
rich, and the ECU stopped responding in any Idle Mixture
adjustment.

Thanks again,
Aristides---------------------------------------------------------------------------

I suspect the ECU runs the engine on the one basic fuelling map at
idle and below a certain RPM.
In cruise mode it will modulate the fuel map according to A/F ratio
feedback, and the A and B banks are modulated separately.
Not sure from your description of lean/rich running if you were out of
idle and feedback was operating.
Faulty wiring to the sensors, or lack of heating if they are heated
versions, or faulty sensors can mess up the mixture.
You would think the degree of modulation would not be very great on
top of the basic fuelling map to achieve good economy.

Trouble is that the original fault you report has now changed, so is
this a totally different problem or related to the original one ?
That makes troubleshooting more complex.

It sounds like the ignition system is not your problem.
Hopefully true, and that eliminates one major source of headaches.

The fact that A and B banks do not appear to have the same fuelling
would point to a problem in the ECU, but also could be a feedback
issue in cruise mode.
However, my guess is that most engine management issues boil down to
faults in sensors providing inputs to the ECU, due to sensors
themselves or wiring or connectors.
In order of effect, the ECU needs to see correct signals from:

Vaccum ( has by far the biggest effect on mixture ).
RPM.
Coolant sensor ( If it has a short circuit or open circuit it can stop
the car in its tracks ).
Air temp sensor.
TPS ( Mostly used for acceleration enrichment, but can be used to tell
the ECU when throttle closed.
Although usually a minor influence, if the signal is noisy
it will mess up the mixture ).
Various throttle or vacuum operated switches to change mixture for
emissions or drivability.
A/F ratio sensors.
Do not forget good grounding is needed for signal integrity.

Next in line is signals out of the ECU to drive the fuel pump and injectors.
Injector wiring and connectors are often culprits.

There are situations where the ECU has been changed and fixed the
fault, but an estimate is less than 10% of fixes.
With all the sensor inputs listed above, depending on the sensors
being correct, the wiring not failing, connectors being tight, good
signal grounding, less than 10% might be a generous estimate.

As Kirbert mentioned, the only way to be 100% sure of an ECU fault is
to swap it and preferably do a double blind test.
If you do not have a spare ECU, and the engine management problem is
time or temperature related, you can alternately heat and cool the ECU
in the car with a fan heater.
See if that changes anything. If it does you can be 95% sure it is an
ECU fault.

Richard Dowling, Melbourne, Australia. 1979 coupe + HE V12 + manual;
1989 convertible; 2003 XJ350.

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16

If it were me, I’d pull the ECU apart and look for damaged components (burnt
copper or resistors, leaky capacitors) and/or resolder any solder joint that
looks slightly suspicious. Usually resolder ALL the connector joints.

The fact that you seem to have a temperature related go/no go points to a
solder joint issue.

In the solder joint, there is an intermetallic bond between copper, any
copper plating (sometimes silver, gold or tin) and the lead/tin solder. With
thermal cycling these can separate (crack) creating a “dry joint” that is
not often obvious, even under a magnifying glass or microscope. Remelting
the solder joint usually fixes them. These types of faults commonly come and
go with heating or freezing. You can buy a can of Instant Freeze
specifically to try to trigger these faults when diagnosing a circuit board.

Electrolytic capacitors leak with age and reduce capacitance as the
electrolyte evaporates or leaks (so they become less effective than they
were designed to be). Sometimes they can be spotted with a swollen case or
goo oozing out of them. Back when these ECU’s were made, long life caps were
measured in 2,000 hrs. Even today they are a problem.

Sometimes there can be a fault inside an actual transistor or IC. This is
usually due to poor manufacturing, where a defect has been manually reworked
or the part physically damaged. Each leg of the part should be hermetically
sealed to the body of the component. If this seal is damaged (by
uncontrolled manual application of heat to fix a solder joint defect) the
part can corrode internally, leading to an age related defect.

Very seldom does a part in a well designed circuit actually fail from “old
age” (except electrolytic capacitors!).

Good luck.

Mark

PS. I should say that a number of Bosch ignition drivers are reported to
have thermal issues due to internal temperatures getting so hot that the
wire bonding comes adrift. They can reportedly be cut open and resoldered
with high temp solder. My experience with these parts is they tend to run ok
when cold but fail when hot.

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17

From photos I have seen, it doesn’t look like there are any electrolytic
capacitors in the ECU. That is good news and indicates the quality of the
original design.-----Original Message-----

Electrolytic capacitors leak with age and reduce capacitance as the
electrolyte evaporates or leaks …

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18

Excellent! You know your electronics. Old age and incessant hot-
cold cycling.

Ptipon
Sonora/CA, 90 XJS-V12 conv, United StatesOn Jan 25, 2016, at 6:35 PM, Mark Eaton wrote:

If it were me, I’d pull the ECU apart and look for damaged
components (burnt
copper or resistors, leaky capacitors) and/or resolder any solder
joint that
looks slightly suspicious. Usually resolder ALL the connector joints.

The fact that you seem to have a temperature related go/no go
points to a
solder joint issue.

In the solder joint, there is an intermetallic bond between copper,
any
copper plating (sometimes silver, gold or tin) and the lead/tin
solder. With
thermal cycling these can separate (crack) creating a “dry joint”
that is
not often obvious, even under a magnifying glass or microscope.
Remelting
the solder joint usually fixes them. These types of faults commonly
come and
go with heating or freezing. You can buy a can of Instant Freeze
specifically to try to trigger these faults when diagnosing a
circuit board.

Electrolytic capacitors leak with age and reduce capacitance as the
electrolyte evaporates or leaks (so they become less effective than
they
were designed to be). Sometimes they can be spotted with a swollen
case or
goo oozing out of them. Back when these ECU’s were made, long life
caps were
measured in 2,000 hrs. Even today they are a problem.

Sometimes there can be a fault inside an actual transistor or IC.
This is
usually due to poor manufacturing, where a defect has been manually
reworked
or the part physically damaged. Each leg of the part should be
hermetically
sealed to the body of the component. If this seal is damaged (by
uncontrolled manual application of heat to fix a solder joint
defect) the
part can corrode internally, leading to an age related defect.

Very seldom does a part in a well designed circuit actually fail
from “old
age” (except electrolytic capacitors!).

Good luck.

Mark

PS. I should say that a number of Bosch ignition drivers are
reported to
have thermal issues due to internal temperatures getting so hot
that the
wire bonding comes adrift. They can reportedly be cut open and
resoldered
with high temp solder. My experience with these parts is they tend
to run ok
when cold but fail when hot.

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exciting services and resources including Photo Albums, Event
Diary / Calendar, On Line Books and more !

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19

In reply to a message from Richard Dowling sent Mon 25 Jan 2016:

Richard,
Thank you for your reply.

You are right, I must check if the signal from the oxygen
sensors and the TPS are arriving to the ECU intact and that
the heating element works OK (I have installed heated oxygen
sensors).

Will do that and report back.

As I have the Feedback Monitor permanently installed in the
trunk I can see very easily and at any time what is
happening with a flick of a switch.
I also have a closed loop switch installed so I can put the
ECU in closed loop at idle.
In normal operation the feedback will oscillate, the two
banks at the same rate and in opposite directions, around a
center point in the scale.
Adjusting the Idle Mixture in reality sets the Base Fuel
Map and it will move the oscillation up or down in the
scale, i.e. leaner or richer.
This is more or less the official procedure of adjusting the
Base Fuel Map, to bring the oscillation as close as possible
to the center mark that is 2.5 volts.
I know it receives some sort of signal from the Oxygen
Sensors because when I disconnect them the ECU oscillates in
a very rapid and distinctive way around the 2.5 volt mark.

Aristides–
The original message included these comments:

I suspect the ECU runs the engine on the one basic fuelling map at
idle and below a certain RPM.
In cruise mode it will modulate the fuel map according to A/F ratio
feedback, and the A and B banks are modulated separately.
Not sure from your description of lean/rich running if you were out of
idle and feedback was operating.
Faulty wiring to the sensors, or lack of heating if they are heated
versions, or faulty sensors can mess up the mixture.
You would think the degree of modulation would not be very great on
top of the basic fuelling map to achieve good economy.
However, my guess is that most engine management issues boil down to

–
Aristides Balanos, 1986 XJ V12,VDP - www.e-psychi.com/jaguar
Roussillon, Provence, France
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20

In reply to a message from Mark Eaton sent Mon 25 Jan 2016:

Mark,

Yes, the ECU is out, I have opened it but I can see no
obvious fault.
Everything is clean, and the varnish intact.
I will resolder all the joints and see if it makes any
difference.

Best,
Aristides–
The original message included these comments:

If it were me, I’d pull the ECU apart and look for damaged components (burnt
copper or resistors, leaky capacitors) and/or resolder any solder joint that
looks slightly suspicious. Usually resolder ALL the connector joints.
The fact that you seem to have a temperature related go/no go points to a
solder joint issue.
In the solder joint, there is an intermetallic bond between copper, any
copper plating (sometimes silver, gold or tin) and the lead/tin solder. With
thermal cycling these can separate (crack) creating a ‘‘dry joint’’ that is
not often obvious, even under a magnifying glass or microscope. Remelting
the solder joint usually fixes them. These types of faults commonly come and
go with heating or freezing. You can buy a can of Instant Freeze

–
Aristides Balanos, 1986 XJ V12,VDP - www.e-psychi.com/jaguar
Roussillon, Provence, France
–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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