problem with my 86 XJ6

Joined: Mar 01, 2007 Posts: 1

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

External Since: Jul 11, 2005 Posts: 57

"mikehype2" wrote in message

>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
>
> --
> Posted at author's request, using fully moderated
> http://www.AutoBoardz.com/Jaguar-forum-24.html interface

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