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Old 04-22-2011, 04:14 AM   #1
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fuel pump not working

Hi, I'm new to this site. I have a 91 YJ 2.5L, four banger, whose fuel pump won't turn on. Jeep was running fine, then began to hesitate during acceleration. I changed the fuel filter, plugs, wires, cap, rotor. I had a feeling none of these things were the problem because they were all fairly new, and I was right, still stumbled when I pushed hard on the gas. So I replaced the injectors, but when I went to turn it on, The fuel pump failed to turn on. I replaced the relay, but nothing. I double checked all my connections from when I replaced the injectors, all looked good. I went ahead and did what I really wanted to avoid, I dropped the tank and replaced the fuel pump. Still nothing. How do I check to see if I am getting power to the pump? The fuel gauge does top out to full with the ignition on, and the tank isn't even close to being full. I'm not throwing any codes other than 12 (battery disconnected recently). I am at a loss. Any suggestions would be helpful.

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Old 04-22-2011, 07:05 AM   #2
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Drop the tank and inspect the pump its probably bad, AZone sells them for just over 100 bucks for pump and screen. Sounds like you spent close to that beating around bush.

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Old 04-22-2011, 07:32 AM   #3
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I think the op said he replaced the fuel pump
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Old 04-22-2011, 07:34 AM   #4
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Check for ground there's been a few people. That have had your same problem it had turned out to be they're fuel pumps.
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Old 04-22-2011, 07:35 AM   #5
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They're fuel pumps weren't grounded
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Old 04-22-2011, 04:07 PM   #6
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Thanks guys, Yes I have already changed out the pump. I will check the wiring again. I'm thinking that's where the problem lies considering that the pump was turning on prior to me replacing the injectors. Can anyone tell me how to use a multi meter to see if I have power going to the fuel pump?
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Old 04-24-2011, 09:46 PM   #7
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Well, went out and got a circuit tester and a continuity tester today, and went to work checking grounds, voltages and continuity. Ground going to the fuel pump is good. Tan wire has voltage at the connector to the fuel pump. Orange wire does not have voltage, but does have continuity. No voltage to the orange wire even where it exits the power distribution center. Getting ready to run a jumper from the PDC to the fuel pump. Other alternative is to open up the PDC to check the connections inside. Any other suggestions?
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Old 04-24-2011, 10:00 PM   #8
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Okay, quicky question, did you check the Fuel Pump relay in the PDC? You might be able to swap it with on of the other relays just to check it.if you have an AC Relay that is always a good one you can live without and won't affect the engine starting.
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Old 04-24-2011, 10:21 PM   #9
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I actually bought a new relay, and even did some swapping between the auto shutoff and the starter relay. Starter worked with any one of the relays I put in.
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Old 04-24-2011, 10:33 PM   #10
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Here is a quick diagram i threw together of the fuel system. Have you checked that power is getting to F9 and through it. and then from F9 to the Fuel Pump relay? Also not Yellow is hot when the key is in the run position, so you should get a 12v reading at that point if you turn the key to run, without having to move to on.
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Old 04-24-2011, 10:40 PM   #11
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I ran a circuit tester to each of the slots for the F/P relay, auto shutoff and starter relays in the PDC. I got a tone in all the slots except the ones where the 87 and 87a (if that means anything to any one) contacts connect on the F/P and auto shutdown spaces (center slot and the other that is in a different direction than the other three. The starter relay slot only gave me a reading on the 30 slot.
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Old 04-24-2011, 10:48 PM   #12
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Sorry Undead, I don't know what ou mean by the F9. checked all the fuses to the relay and all were good. Is that what you were talking about?
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Old 04-24-2011, 10:50 PM   #13
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If you had the relay in, 87a would have a tone when the the relay is NOT energized. 87 will have a tone when the relay is energized. So when the pump is supposed to be on 87 will be active. And when the car is off 87a will be active.

30 is the source of the switch and the power flows from there to 87 or 87a depending on whether there is current through the inductor (between the yellow and org/grn wire on the diagram)

you should be able to stick a thin wire in the slot for 87, making sure not to touch any of the other contacts, stick in the relay and test it.
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Old 04-24-2011, 10:52 PM   #14
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With F9 if you are getting a signal at socket 30 on the Fuel pump relay that means the circuit from F9 to the relay is good and eliminates another portion.
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Old 04-24-2011, 11:00 PM   #15
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Ok, ran wire to 87 and got NO tone. Does this mean the relay isn't working? Or is it something inside the PDC?
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Old 04-24-2011, 11:10 PM   #16
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If that is with the Key on in the run or start position, the relay is bad or the metal part of the wire is missing the contact. If you jumpered a wire from 30 to 87 the pump should run that would be your second opinion on the relay. just don't leave it in there too long.
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Old 04-24-2011, 11:15 PM   #17
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do I jump the wire with the relay in or out
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Old 04-24-2011, 11:19 PM   #18
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Either but it will be easier with it out because you want to be able to poke it in, see if the pump works then pull it out.
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Old 04-24-2011, 11:24 PM   #19
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I did not hear the pump come on when I put 30 to 87. tried key in on and run.
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Old 04-24-2011, 11:31 PM   #20
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I'm gonna try to open up the PDC and check the connections inside.
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Old 04-24-2011, 11:34 PM   #21
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So you have 12v at 30.
No voltage at 87 with the relay in and the key in the run position.
I assume you can see the metal contacts in the relay socket, and none of them look super corroded.
jumpering 30 to 87 doesn't get the pump to run.
You can try jumpering from the hot side of F9 to 87 and see if the pump goes on. If not there has to be a problem at the pump, the wiring to the pump or the ground at the pump.
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Old 04-25-2011, 12:54 AM   #22
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for fun i decided to hook up the old fuel pump and wouldn't you know, it's working now. GRRR!!! Everything you have suggested is working, on the old pump. Even with the relay in. Ran a direct wire from 30 to the new pump and nothing happened. I'm gonna check the ground at the pump and if that checks out to be good, then tomorrow I'm dropping the tank and reinstalling the old pump. Earlier today I reinstalled my parking brake after removing it to replace the front speakers. A gift to myself for a job well done after replacing the manifold gasket and cleaning out the manifold and throttle body. Both needed to be done, and after everything else I had done I thought for sure this would fix my sluggish acceleration. Then the fuel supply problem. Unfortunately I did the speakers before the engine work, and didn't finish reattaching the parking brake. While installing the parking brake, today, I reattached a ground wire. Tony 76 you might have been right about that ground. I'm starting to think that might have been why the old fuel pump wasn't working in the first place. The new pump might be faulty as well. I did get it rather cheap off ebay. I'll repost tomorrow to let you know what happens. Undead thank you so much for your help. I learned a lot. Someone on another thread gave you high praise, I can see why. You are a Guru.
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Old 04-25-2011, 10:27 AM   #23
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I see that at work a lot where we get a part in to replace a broken part and the new one is just as bad or worse. With mechanical stuff you can usually see the problem before you install but electric and electronic stuff is a bit trickier.

Hope this solve your problem and you back behind the wheel letting her remind you why you put up with her faults.
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Old 04-26-2011, 05:53 PM   #24
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Sorry for the delay. Last night I dropped the tank, again, I'm becoming a pro at this. Good ground on new pump, but no power getting past the connector. Inspected old pump before reinstalling, and found a big gash in the rubber hose from the pump to the sending unit. There's the reason the Jeep was hesitating during acceleration. Swapped out the hose, reinstalled old pump, and put everything back together. My baby's running like a champ now. Hooray! Now that it's running though, I can see the new gasket I put on the valve cover didn't seal properly. Hands prepare to get dirty... again. Oh well, working on her is half the fun. Now if I could just find time for the other half. Thanks guys, this forum is awesome. Hope I can be as much help to some fellow Jeepers out there as you guys were to me.
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Old 04-26-2011, 10:37 PM   #25
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Hooray! No more leaks! Everything is working good! Now I can finally use that can of engine brite I bought.
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Old 04-27-2011, 02:06 AM   #26
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Good job. and thanks for updating us on the success.

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