Fuel pump wont prime
 

Hey guys looking for help, I recently purchased a 97 Cherokee with a blown motor just finished installing a used motor everything is hooked up. The motor cranks but the fuel pump doesnt prime at all and I have power to the fuel pump . I've checked the relays and fuses they are all fine and it's a new pump I've tested the pump with a 12v source and it works I'm just at a loss I dont know what else to check any help would be greatly appreciated.

Do you hear the pump running? Don't tell anyone but now and then I'll stick a hose in the tank filler, then try to get a seal there maybe with rags or anything stuffed in some some plastic. Then blow repeatedly on the hose sealing the end with your tung. Thus you can pressurize the tank with air to prime a stubborn situation.

Understand the pump will only run a couple of seconds with ign on, then again cranking, then again when the puter figures the engine is running. You might with a helper depress the dealie on the Schrader valve (LIKE tire valve on the fuel rail) Repeatedly turn the key on/off every few seconds while air is vented from the Schrader valve.

Yea I get that part but the pump doesnt even turn on I hear no noise comming from it and I checked the Schrader valve on the fuel rail and no pressure in it

Have you tested to confirm that spark is present? I ask because folks on this forum have said that if the CPS signal is missing, that the computer will not command the fuel pump on (via relay). If you have spark present, that would show that the computer is picking up a signal from the CPS, and rule it out. If you get no spark, then you might be looking at a CPS connectivity problem. I'm going this direction because you have already confirmed power to the pump with a direct 12v test, implying that the computer is not commanding it on via the relay.

Because I don't know how you tested it with direct 12v. Did you do that by jumping the relay in the PDC? That is a good test because it checks the connectivity all the way from the PDC back to the pump (instead of just applying 12v at the pump connector).

Ok cool I will check the spark tomm I need to buy a tester for that, and I did replace the cps just to be on the safe side but as far as testing the pump i ran a 12v jist from the battery to it so i could see if it was my pump but I will def check my spark tomm for sure

Don't forget to test the pump by jumping the fuel pump relay. This will rule out any wiring problems between the PDC and pump, and pump to ground.

Yea I did jump the relay and nothing happened too ... do you think it's my ecu ?

If the relay has a 12v+ constant (which it should) and if you jump the relay properly (between the two larger sockets), and there is no pump activity, then there is an electrical connection problem between the relay and the pump, or between the pump and its ground connection. The computer is not involved when jumping the relay (it is providing power directly to the pump).

The most likely culprit is the fuel pump connector, which you should double check. Make sure it is all the way connected, and not hung up on the weather proof gasket material that is inside the connector. If you never touched the pump during your motor swap, then I would more suspect that something got pinched or jostled during the job.

Ok cool I will check that where are the grounds for the pump located ?

I believe the ground for the pump is located behind the trim panel on the driver side rear of the vehicle (behind the spare tire). However, testing the ground from the connector with a multimeter would probably suffice, I wouldn't pull the trim unless you detect a problem with the ground and need to investigate.

Yea I only say that because I do have power to the connector it's just nothing turns on thats why I wanted to check the grounds ... I'm just so stumped with this thing man I dont get it hoping its somethn simple

On my '96XJ, the camshaft position sensor has caused a no spark condition, same as the crankshaft position sensor does.

What works?
The fuel pump is pumping fuel? Why not just leave the 12V hooked up and start it?

I've replaced the cps and last time I ran a constant 12v source one it never stopped priming and two I burned the pump up in the process

Guessing he means just to see it prime and run. Disconnect it if it doesn't prime in a few minutes. I had one where you could hear the pump run but got no fuel. The pin that secures the impeller to the pump shaft had sheared!

Understanding the relay sockets can help allot. Mine and yours are probably different BUT you have one from there should go straight to the pump, energized when another is grounded by the puter. Maybe another with full time power from a fusable link and one powered with ign on.