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1993 Jeep YJ 1993 yj wont start no power to fuel pump?

Tiny
YJJEEP
  • MEMBER
  • 1993 JEEP WANGLER YJ
  • 6 CYL
  • 4WD
  • MANUAL
  • 185,000 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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Monday, August 30th, 2010 AT 8:14 AM

14 Replies

Tiny
WRENCHTECH
  • MECHANIC
  • 20,758 POSTS
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.
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Monday, August 30th, 2010 AT 8:43 AM
Tiny
YJJEEP
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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.
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Tuesday, September 7th, 2010 AT 9:08 PM
Tiny
WRENCHTECH
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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.
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Tuesday, September 7th, 2010 AT 9:13 PM
Tiny
YJJEEP
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  • 7 POSTS
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.
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Friday, September 10th, 2010 AT 6:07 PM
Tiny
WRENCHTECH
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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.
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Friday, September 10th, 2010 AT 6:32 PM
Tiny
YJJEEP
  • MEMBER
  • 7 POSTS
Put ground to blu/yel and relay pulls in and light at fuel pump energizes.
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Monday, September 13th, 2010 AT 3:24 PM
Tiny
WRENCHTECH
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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?
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Monday, September 13th, 2010 AT 3:29 PM
Tiny
YJJEEP
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  • 7 POSTS
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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Tuesday, September 14th, 2010 AT 11:23 AM
Tiny
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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.
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Tuesday, September 14th, 2010 AT 11:33 AM
Tiny
YJJEEP
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  • 7 POSTS
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.
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Tuesday, September 14th, 2010 AT 1:40 PM
Tiny
WRENCHTECH
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What we're looking for here is a 2 second pulse of "on" time. Your going to have to run all the same checks on the ASD relay and see if it is acting the same way.
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Tuesday, September 14th, 2010 AT 1:50 PM
Tiny
YJJEEP
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Ran the same test on the ASD relay. Relay will pull in and output will light up. However I still have no response when I turn on the key-nothing.
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Wednesday, September 15th, 2010 AT 4:27 PM
Tiny
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I want to verify all the power or ground inputs to make sure they are working. It's starting to look like a bad ECM but I don't want you to buy one without someone else verifying it.
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Wednesday, September 15th, 2010 AT 4:38 PM
Tiny
FYRBUD
  • MEMBER
  • 1 POST
For what it's worth.
Same Jeep, similar mileage. Will crank but not fire. Blower fan and windshield washers not working. Both Fuel pump and ASD relays have power to pin 30 for contacts, but neither has power to either side of their relay coils. Jumped contacts on Fuel pump relay and heard the pump kick on. Replaced ignition switch, no improvement. All fuses good, especially fuse #9 (Ign/lps) under the dash. FRUSTRATED.

Split the fuse block and started tracing wires. Manipulation caused turn indicators to work intermittently. Aha! More manipulation caused a couple of fuses to fall out. Hmmmm, I noticed the fuses were waaaaay too easy to pull out. Also found a blog where a YJ owner discovered JEEP MOVED THE IGNITION WIRE FROM IGN/LPS TO THE DOME FUSE in 1992 or 1993 without relabeling the fuse block. I removed the Dome fuse, cleaned the contacts and as I reinserted it I heard the fuel pump kick on. All the problems seem related to poor/dirty/loose contacts inside the fuse block. Twisting the legs of the fuse, just a little, seems to increase tension and conductivity. Pay very close attention to fuses #9 and #5 as one or the other supplies the power to the coils of both relays (and maybe the PCM module). Good luck!
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Sunday, April 19th, 2015 AT 9:14 PM

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