Fuel injection

["Alex" <tid.rum@swipnet.se>]

Friends,
Just had some experience regarding intermittent rich running, lack of 
power, incorrect idle speed and high fuel consumption on my V-12 H.E 
engine.
First cause was found to be the throttle potentiometer.
Due to the price of a new one here in Sweden (>300USD) I started with 
taking it apart (yes, there are 3 screws from the bottom side, 
covered with plastic filler). Once I found the cause of the problem 
(the conductive plastic was worn out by the contacts) I figured out 
that by carefully making a S-bend on the contact arms, I would move 
the contact points a little bit closer to the center and by that 
making contact to a unused part of the contact path.
Said and done, half a year later it is still working.

But the similar problems occured again.
Checked the pot. once more but still worked fine.
Measured the resistance of the air and water temperature sensors (as 
I had already done once before) but neither of them showed any sign 
of malfunction. One day I just came to the thought that I wanted to 
measure these sensors under normal working condition, as the have to 
be disconnected from the ECU when measuring the resistance.
So I connected a high impedance digital voltmeter to the water 
temp sensor.
The ground wire connected to the engine block and "hot" wire to one 
of the female connectors on the side where the cables goes into the 
connector housing.
One of the connectors should give ~2.4 Volts with the ignition on.
(The other one gives 0 Volts)
Starting up, meter under the wiper, taking the car on a test drive, I 
could watch the voltage decrease to ~0.95 Volts at normal temp.
Suddenley it jumped up to 2.1 Volts and I could feel the lack of 
power simoultanesly. Then, just as unexpected, the voltage dropped 
down to 0.95 again. Bingo!!!

Next challenge: finding a new sensor to a reasonable price.
Called my Jag dealer and asked: ~90USD, but I got the part number 
f.o.c (DAC 4737)
Called a Bosch dealer, gave him the Jaguar p/n, he cross checked and 
found a replacement (0280 130 055). Unfortunately only available in 
Germany. His list then referred to 0280 130 026 which they had in 
stock. Price? ~30USD. Bought it, installed it, measured it comparing 
to data in Kerbert's Experience in a Book, and my car runs perfect 
(up to 19.5 MPG on open road).




Alex
1986 XJ-S V-12

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