Ok I am slowly getting some of these issues resolved. But this one is getting old. If my 93 grand cherokee with a 4.0L 134XXX miles sits over night it takes several times of on/off with the key and sometimes several attempts of actually rolling the motor over before the fuel pump kicks in. I can hear it. If it has been sitting for more then about 5 minutes I have to turn the key on and wait maybe 30-45 seconds before I can hear the pump prime. Sometimes I have to on/off the key a couple times before the pump primes. If it has been sitting less then 5 minutes the pump seems to prime pretty quick, within a few seconds. Almost like I have a delay in the electrical pulse getting to the pump? maybe?

Side note. When I park the jeep and walk away from it I can sometimes hear a pop sound from under it. Almost like a pressure relief?

Help please, is it the fuel pump?

Do all Cherokee's have this many issues? I have never bought a used rig with so many issues.

 

I would consider the fuel pump relay first.

 

I agree. I'd look at the FP relay and also the ASD relay. Make sure their contacts are clean and corrosion free as well as the fuses in the PDC under the hood. Try putting your hand on the FP relay while a friend turns the key from off to run and feel if it clicks right away, if it does but you're not hearing the FP prime then then there's a good chance the problem is the pump or the wiring to it. If the relay does NOT click as soon as the key is turned to the on position then the problem is most likely the relay, the ECM, or maybe even the ignition switch or the wiring between.

 

Hi folks, I bought a new fuel pump relay today and it made no difference. I have not tried feeling the fuel pump relay as someone turns the key on yet. Hopefully tomorrow. What is the ASD relay??

Thank you very much for your help

 

ASD stands for Automatic Shut Down. It's a relay that will kill the power to fuel pump, ignition coil, and injectors when you turn the key off or if signal from the crank sensor is lost. Its' right there in the PDC along with the FP relay and a few others and should also click as soon as the key is turned from off to run.

 

When you first turn key on the fuel pump only gets a momentary "prime" signal for 1-3 seconds. After the 1-3 seconds the PCM will not trigger the fuel pump unless it verifies the engine is running.

So if you are not getting that initial 1-3 second prime, I would suspect the ASD relay like mentioned above. It could be something else but try this first since its easy and cheap. Also check battery connections, terminals and grounds etc.

 

Just read on another forum where a guy had the same issues and it turns out his pcm was going dead. Swapped one from a junkyard and it works perfectly. Just one more thing to consider.

 

Hi folks. I was able to get some help while working on this beast. We wound up changing the relays around and no better. Turn the key on and it generally takes a few minutes before the pump primes. It is getting worse every day in the day in the starting department. All of my battery connections are in very clean condition. New battery even. PCM was changed for a few minutes and it did not make any difference. I am getting tired of this issue. Thank you everyone for your help!

 

Resolved::::: Bad capacitors in the pcm. Replaced and life is good.