[Jeepmark]

Im not getting any fuel through my 94 4.0 zj, Wondering if anybody knows how to bypass the fuel relay so the pump is running constantly...ive been having problems with my pcm and dont want to change the pump just cause its "not working" it just might not be getting any power. Also i changed the fuel filter with a slim chance that was the problem and it wasnt. any help with this would be greatly appreciated seeing how my car is just sitting.

[greasefingers]

When you turn the key to “on” and not “start” do you hear the fuel pump motor whine? If no then your fuse, relay, or pump is fried. If yes then you are not out of the woods yet. You must measure the fuel pressure at the fuel rail. A schrader valve is provided for a pressure gage adaptor. It should read between 32 to 42 psi. Jumping the relays (automatic shutdown & fuel pump relay) is not a good idea and will require a Haynes manual. The crankshaft & camshaft sensors can also cause the two relays to trip. The best way to jump this; only for a test, would be to run hot & ground directly from the battery to the fuel pump motor connector. However it requires long jumpers (easily made) with an inline fuse in the hot lead.

[bnhcooper]

I'd start with the fuses, check them for the fuel pump and the PCM. Then check the relay. The relay is in the PDC behind the battery. When someone turns the key to the on position, you should hear a click as the relay works. If no click, take the relay out. I wouldn't recommend jumping it, but if you're brave do it at your own risk. With the key on, you should have battery voltage at the spot for terminal 30. The power goes to the fuel pump at terminal 87. Again, I don't suggest doing that. Further diagnosis can be done as follows.

Somone else will need to back me up on this next part. The PCM grounds the coil in the relay through terminal 85. So I think, with the key on, you should continuity with ground at the spot for terminal 85. Don't try this until someone else confrims it, because you don't want to fry the PCM. If this is correct, though, and you don't get the continuity, it means the PCM is bad and not energizing the relay. Given that you have an energizing signal and power to the relay, next you need to test the relay. Here's how to do that:

1. Remove the relay before testing. Use an ohmmeter to check resistance between terminals 85 and 86, should be 75+/-5 ohms.
2. Connect the ohmmeter between terminals 30 and 87A. The ohmmeter should show continuity.
3. Connect the ohmmeter between terminals 30 and 87. Should be no continuity at this time.
4. Connect one end of a jumper wire (16ga or smaller) to terminal 85. Connect the other end to the ground of a 12 volt power source.
5. Connect one end of another jumper wire (16ga or smaller) to the power side of the 12 volt source.
Do not allow ohmmeter to contact terminal 85 or 86 during this test
6. Attach the positive jumper wire to terminal 86. This activates the relay. There should now be continuity between 87 and 30, but not 87A and 30.
7. Disconnect the jumpers and replace the relay if it did not pass any test.

Given that you have power, the PCM is sending a signal, and the relay is good, the only other options are a break in continuity from the terminal 87 to the fuel pump, which could be tested with a long jumper, or a bad fuel pump.

Hope you get something useful out of this.

[Jeepmark]

ahh, that is exactly what i was looking for...you da man i had an idea about what was going on i just dont have a chiltons or anything im just shootin the dark about everything i do. ill test that out and tell ya how it goes

[bnhcooper]

Glad I could finally help someone! Post again if you get stuck or need some more advice, the guys on this forum are great. Hopefully someone will comment on that terminal 85 check just to put my mind at ease.

[greasefingers]

Yupper, that's correct. The PCM grounds the both relays via terminal 85.

[bnhcooper]

Well there we go, Thanks!

[Swamp Boy]

I was just going to suggest running a wire from a toggle to the black with red tracer wire on the pump plug.. That would be direct power to the pump..

But ....Ummmmm.... Yeah... yours way works to...

[bnhcooper]

Sorry, yeah I guess it would work. I spent three days in BFE when my fuel pump died in my Camaro. The mechanic tried to hotwire it and dang near blew up the car. He then proceeded to fry the relay by power testing the wrong terminals, and then fried the ECM by sending power to a ground. So I get nervous around the whole area. Just offering advice.

[Jeepmark]

You guys rock! im so glad there are people on this forum that know what there talking about...thanks again

[greasefingers]

You have had PCM problems so eliminate it first. As bnhcooper stated, listen for the two relays to click. You can also place your finger on them and feel them energize. This would mean that the PCM is grounding correctly, if the relays are not bad. You can also play “musical relays” since many of them in the power distribution center are of the same type. Just do not swap the automatic shutdown relay with the fuel pump relay because the automatic shutdown relay supplies power to the fuel pump relay. The relays can only be found at the dealership, and cost about $ 8/ea. If they than the next step would be to disconnect the electrical connector at the fuel tank and check for 12 volts. If you have 12 volts then you need a new fuel pump or the connector was loose.