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1998 Jeep Cherokee Fuel Relay Ground

kevashmore

NAXJA Forum User
Location
Midland TX
Back Story:
I have a 1998 Jeep Cherokee XJ with a 4.0L and have had the issue of needing to prime the fuel pump before starting for the last 3 years. (I have only driven it approx 5k miles in the last 3 years). Finally, it wouldn't start and I pressed the fuel rail schrader valve and had no fuel pressure.

Current:
I ordered a new fuel pump and installed it over the weekend only to discover that it still wouldn't start. Upon further diagnosis, I found that the fuel pump relay is not getting a ground through the ECM. I Tried 3 new relays for the ASD and Fuel Pump and checked them on a bench and the relays are good. I can jump the relay(50 psi fuel pressure) and the jeep fires up and runs fine (wouldn't do that before I replaced the fuel pump), the ASD relay gets a ground so everything is working properly except the fuel pump relay. I been searching forums and haven't found anything concrete other than people have replaced Crank position sensors, cam position sensors, ECM, Ignition Switch, ect. but I want to know that I am going to fix it before I throw parts at it.

I guess my main question is looking at a wiring diagram (Haynes manual) it looks like the ASD and fuel pump relay share a ground through the ECM. Something is preventing the relay from operating even the 2-3 second fuel pump prime when you turn the key on(which should still work even with a bad cam/crank position sensor).

I know I can install a relay that would ground the fuel pump relay with the key on or a switch and it would let me drive all I want but there has to be something I am missing.

Any suggestions on what to check. There are no codes with a scan tool.
 
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