problem with my 86 XJ6

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mikehype2 - 05 Mar 2007 04:30 GMT

I have a nifty problem with my 86 XJ6 that even seasoned mechanics
can’t get. The problem started with the MAF and I have replaced it
with a new one. The car will now not start and run. Here comes the
fun. If I remove the relay which I think is the "start"
relay.....nothing, won’t start. If I remove the "run" relay the car
will start and run with difficulty. If I plug the run relay back in it
kills the car. Now yes I reversed the relays and the same thing
happens. With the MAF door open I test the fuel pump voltage (with the
run relay in place) and have a good 12 volts. By the way the pump puts
out 37psi. now, I tried replacing the ecu also but to no avail. Ok
now, like I said I got the car to run with only one relay in place but
the fun is about to begin. With the car running (poorly, richly, and
delicately) I quickly and I mean quickly changed the relays by
replacing the run relay and removing the start relay and the car
sounded great for all of 1 second and died. Hmmm. I just don’t Know.
Any thoughts at this point would be of great help. One "mechanic"
told me to keep replacing parts and It will eventually work. Sure,
thats the ticket. Anyway, Thanks, Mike

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Don Young - 06 Mar 2007 02:56 GMT

>I have a nifty problem with my 86 XJ6 that even seasoned mechanics
> can't get. The problem started with the MAF and I have replaced it
[quoted text clipped - 14 lines]
> told me to keep replacing parts and It will eventually work. Sure,
> thats the ticket. Anyway, Thanks, Mike

I do not have the wiring diagram handy and am not experienced with your
particular car. However, most fuel pumps do not get 12volts when the engine
is not running. There is usually an initial pressurization run of a few
seconds. Some vehicles will also run the pump when the starter is engaged.
Then the ECU generally monitors the crank position sensor pulses and applies
power to the fuel pump relay only as long as the engine is running. If the
engine should fail to start or stall, the pump is stopped to prevent a
hazard from fuel leaks in case of accident, etc..

I have no idea why you have the symptoms you describe with the relays. A
mechanic with a good understanding of the system and the wiring diagram
should be able to sort it out, though. Replacing parts does not always fix a
problem. You might check carefully for disconnected or poorly connected
wiring in the areas you have been working around.

Good Luck, Don Young

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Jim - 18 Mar 2007 17:43 GMT

You may have a faulty ECU which can give off misleading symptoms as it is
the "OverLord" of the electronics. I would start as the last responder
suggested by checking connectors and cleaning them with connector(contact)
cleaner. As I have an 87 XJS that has known chafing issues in the wire
looms, I would next check for chafed and/or shorted wires. If that fails,
then I would sart replacing less costly components. However, I think you
might find something in the above first. Happy Hunting!!

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