cwremillard

I am working on a 1989 cherokee xj with a no run issue .the truck fires up while cranking but when you release the key to run position it dies.I have tracked the problem to the fuel pump relay which i have found 2 issues. First issue is The "hot at all times " line to relay(terminal 30) is dead and i cant find the reason i have checked all the fusible links that i can find and they all seem to have power on the down stream side.Secondly the ground side of the control portion of the relay(terminal 86) which if my scematics are right seems to go to the ecm doesn't seem to be doing anything(does the ecm control the negative side?). I have direct powered both these lines and can get the truck to run but can't find the failure point.Any help would be greatly appreciated .On a side note does anybody know what the wires that are on the non activated side of the relay(terminal 87a) go to?

boxburn

I can only talk from a 1995 perspective but if any of this is the same, it may help.

The ground of the relay is indeed controlled by the PCM, the auto shut-down relay pin 86 and fuel pump relay pin 86 are both linked and controlled together.

Pin 30 should be hot at all times so all you can do is keep searching for the reason why it isn't. I'm not sure what it's like underneath the PDC but you may find corrosion or a broken link, maybe even a snapped wire.

With the ignition on or during start, pin 85 of both the ADS relay and fuel pump relay should both be live.

On my XJ, pin 87a is not used and the slot in the PDC for the relay simply has no contacts for the pin, even though the relay does have the pin.

318SixPack

Guessing you already checked the relay with a relay swap or meter?

My only experience is with my 1996 XJ and the only time I had trouble with the fuel pump not coming on was fixed with a new relay.

Also, recently I had trouble with the auto shutoff circuit (per code via the key switch) and a relay replacement fixed that too. That one the trouble code description mentions the relay and that was the easiest thing to check.

lawsoncl

"the truck fires up while cranking but when you release the key to run position it dies"

Have a look at the fuel pump ballast resistor. It's the white ceramic thing screwed to the drivers side fender just above the airbox. While cranking, the fuel pump gets full voltage. As soon as you release the key, the circuit goes through that resistor to reduce the voltage. It was added to reduce the noise from the pump, and eliminated from the design in later years. If it's broken, you can just connect the two wires and eliminate it. It's also a convenient place to check voltages and current to see if the pump is getting voltage and running (should see a around 3 volts drop across it if the pump is running and drawing normal current).