Re: XJ6 S3 Rich Cold Idle

[Randy Wilson <randy@taylor.infi.net>]

On Nov. 26th:
>
>
>My problem seems to have been solved with the following fix received from
>Earl Parkhurst. This after many and horribly expensive efforts over many
>months and mechanics, and replacement of anything that might possibly have
>been the cause. Statues to Earl are being erected in the city as we speak,
>but thanks to all who offered other thoughts.
>I'm impressed with whoever diagnosed this, as most diagnostic equipment
>would have masked the problem when connected up (in a seperate communication
>Earl explains that the problem is a circuit resonance for the cold values of
>circuit components).
>...
>Ian Grant
>
>......if you remove the cap that
>>covers the cable connection to the mass airflow meter, you will find a
>>seven pin connector under the rubber boot.  Solder a 25mfd electrolityic
>>capacitor from pin 3 to pin 5 and it will clear up your problem.  I had the
>

I've been wanting to play with this since it was posted. So, of course, it
was two months until I had a car in the shop with the problem, and free
time to look at it. 

A recap of the symptoms. soon after a cold start the engine will display 
a condition of slightly rich at idle, but goes *extremely* rich under
load. Lots of black smoke, and won't rev. "Chugging", to put it in common
customer terms.

A quick system check showed the standard stuff; a coolant temp sensor out
of spec, a totally open air temp sensor, a bad non-return valve, and
cruddy grounds. But before attacking any of these, while the condition was
still duplicatable, I put a lab scope across the pins mentioned. For
the record, from the front of the car, the 3rd pin is logic ground and the
5th is 12v power. Basicly, we're looking at the fuel injection power. The
scope showed the normal inverted sine wave pattern of a rectified 
alternator... Plus a fairly large surge (2-3v) at a low frequency. Revving
the engine caused this low freq surge to expand, and finally it went
totally wacko, exactly at the time the engine started missing badly.
A bit of probing around located the source of the low freq noise; the
injectors. I then clipped a 22mfd cap across the lines. This totally 
eliminated the alternator noise, and removed all but the slightest trace
of the injector surge. while playing with this, removing and installing
the cap and watching the scope, the car hit the critical temp and
the symptoms disappeared.

 So, it does appear the cap will fix the problem. however, I am unconvinced
this is the root problem (no cap, ie design flaw). Jaguar is the only
company I know of that disregarded Bosch's standard L-Jet installation rules.
The big one broken is hooking the injection power supply feed directly
to the battery (BIG cap). instead Jaguar pigbacked it on the same
power distribution lug with everything else. I am of the opinion that 
the root problem will be a temperature affected bad connection. Tomorrow
morning I will chase farther upstream to see if I can find the start
of the noise. My first attack points will be grounds and power either
side of the main relay.


   Randy K. Wilson
     randy@taylor.infi.net

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