Mechanics

WONT START NO POWER TO FUEL PUMP?

1993 Jeep YJ

Electrical problem
1993 Jeep YJ 6 cyl Four Wheel Drive Manual 185000 miles

The Jeep has sat in my garage for some time wemnt to start it and it will crank, has spark, but fuel pump is not turning on. Fuel pump worked out of tank. I have tested all wires to fuel pump, nothing. Checked all fuses and relays all okay. I replaced the ECU with a rebuilt one, the old one was badly corroded and still nothing. I have cleaned up and replaced some of the ground wires. This has been really frusterating! Any help would be greatly appreciated. This Jeep is my girl friends baby and she really misses it. Thanks.
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Yjjeep
August 30, 2010.




You can eliminate anything with the PCM because it uses the same wire to trigger both the ASD relay and the fuel pump relay and you have spark so you know that works.

Your going to have to do some testing at the relay and see that you have 2 power supplies coming into it.

Wrenchtech
Aug 30, 2010.
Sorry I haven't been able to get back sooner. I have power to one terminal when key is on/off, and I have power to another with key on.

Tiny
Yjjeep
Sep 7, 2010.
Now, the other 2 wires are.

1) the output feed to ignition, injectors, etc. (Heavier wire)

2) trigger ground from the PCM

If you ground that wire, it should energize the output to prove the relay works.

Wrenchtech
Sep 7, 2010.
Okay. The wires on the back side of the relay are: Red/wht positive always hot

Wht/yel positive on with key (also when I traced, it is tied into the dome light fuse this apppears to be factory)

Grn/blk out directly to the fuel pump positive

Last wire

Blu/yel from the ECM

With this I jumped the wht/yel to the grn/blk put test light in place of pump and when I turn the key on I have light, turn the key off and light is gone. Bingo right! I hope that this is helpful.

Tiny
Yjjeep
Sep 10, 2010.
That test didn't prove anything except that the wire is not broken going back to the fuel pump.

With key on and both power supplies present and the relay in place, apply ground to the Blue/yellow and see if you get the same result. That will be testing the relay. If that works, then you still haven't found your problem but you have eliminated the relay and wiring and you know the PCM is not turning it on for some reason.

Wrenchtech
Sep 10, 2010.
Put ground to blu/yel and relay pulls in and light at fuel pump energizes.

Tiny
Yjjeep
Sep 13, 2010.
OK, that means there is nothing wrong with your fuel pump circuit and the computer is refusing to turn it on for some reason. Double check that again with 2 people because I need to know first, if it comes on for 2 seconds when the key is turned on, then again when the engine cranks. How is yours responding?

Wrenchtech
Sep 13, 2010.
With ground on blu/yel. When I turn the key on and test light in place of fuel pump. The fuel pump is energized I counted for tweenty seconds and the light stayed on the whole time. When I cranked the engine the light went out.
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Tiny
Yjjeep
Sep 14, 2010.
Of course it will. Your the one that grounded the wire. It's the PCM that is supposed to do that. Read it without manually grounding it.

Wrenchtech
Sep 14, 2010.
Okay misunderstanding sorry. When I turn the key to the on position, I get nothing at the fuel pump. When I crank the engine, I get nothing at the fuel pump. This is what I have had.

Tiny
Yjjeep
Sep 14, 2010.

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