lasershark

Wondering what triggers the fuel pump? fuel pump relay is good, asr relay is good and fuses under hood are good...

Thought the fuel pump took a crap because I wouldn't hear it prime. Today I replaced the fuel pump (bosch) and it still wouldn't prime. All the gauges still function and it cranks like normal just no fuel pump. I don't know enough about jeep electrical to know what to trace as far as fuel pump triggering goes.

What are all the things I should check or test that would cause the fuel pump to not prime???

Thanks!!

LadyKenai

you could verify voltage at the fuel pump connector with a multimeter see what that gives you..


marc

Bugout4x4

And if you do have voltage then the ground connection could be broken or bad.

94XJCherokee

Bugout4x4

Really? I wonder why they would tie that into the ignition on prime cycle? Man I hate when they do stuff like that.

94XJCherokee

Bugout4x4

During prime cycle the engine isn't even turning over for the sensor to read it. lol

lasershark

Thanks for the help everyone!
So I'll check power at fuel pump relay, then fuel pump connector (if relay is getting power), then I will check the cps.

could the camshaft position sensor inside the distributor also cause the no fuel pump power?
edit:
I am getting power to fuel pump relay and also asr relay
I am also getting no spark, tested with timing light...

Probably looking at cps failure? still need to test that

jordan96xj

CPS and cam sensor are generally not implicated in a fuel pump priming problem.

First step for most people is to jump the Fuel Pump relay in the PDC to determine whether the fuel pump activates when power is manually provided (by jumping the relay). If the fuel pump activates, that helps push the diagnosis towards the control side of the relay. Where positive is provided via the ignition switch, and ground is provided via the PCM.

If the fuel pump does -not- activate when jumping the fuel pump relay, then fuses should be checked (in the PDC) and the problem will usually be between the PDC and the fuel pump. This can included bad wiring, bad pump, lack of ground to pump, etc. The passenger side rear trim behind the spare tire can be removed to inspect the various connections in that area, some of which are ground connections to the body. This is where the fuel pump receives its ground from. It is not uncommon for this area to have corrosion problems over time and ground connections fail causing issues with fuel pumps, and rear lighting (primarily).

lasershark

I did try to jump the relay (pin 30 to pin 87) and pump still didn't prime.
The fuses under the hood all checked out, is there any fuses in the cab that relate to the issue? Not familiar with PDC acronym?
I will check out the grounds.

edit:
ok I lied, jumping the relay turned the pump on. The jeep ended up firing up a few times but now its back to no spark so I am thinking I may have just not have heard the pump the first time I jumped the relay...
When I put the relay back in and it was running it was fumbling around and losing rpm's so I think you are right about the grounding issue...

Now that its back to no spark I think it may be the crank or cam sensor crapping out for ignition and bad grounding for fuel pump relay circut

so to recap
jeep started 5 or 6 times, with the relay jumped it ran good. relay back in, it would stumble with low rpms. back to jumping the relay, it ran good again.
then after the 5 or 6 starts it won't run again even when jumping the relay. No spark again...

lasershark

Ok so I went to costco to do some shopping and when I came back the Jeep fired right up with jumping fuel pump relay. I let it run for a bit, up to operating temperature. Shut it off and immediately tried to restart it and what do you know... No spark again.

I am getting 12.2 volts at ignition coil pigtail when cranking, (ignition coil is new)
distributor pigtail I am getting 5.5 volts (that mean its bad?)

I don't get why it will periodically start every once in a while then go back to no spark???

Any ideas would be appreciated!!

94XJCherokee

lasershark

Ok I will test that next,
thanks

Bugout4x4

I know, Just bugs me that they designed it this way. There are other ways to do it without disabling the fuel source that way.

lasershark

So the CPS tested good with the ohm meter. Can the sensor still be bad but pass the ohm test?