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rpmdiag
rpmdiag, Tech and Instructor
Category: Jeep
Satisfied Customers: 6848
Experience:  Since 1975
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1993 Jeep Grand Cherokee Loredo 4.0. Stalled and cranks but

Customer Question

1993 Jeep Grand Cherokee Loredo 4.0. Stalled and cranks but won't start. Suspect PCM, but not sure. Have replaced rotors, coil, CPS and tested voltages on TPS and a few other sensors. When I do the 5-turns on the ignition, I receive no error codes on the engine lamp.
JA: Have you checked the engine's fuel supply? And the spark plugs -- are they all working?
Customer: Yes. Fuel pump is pumping, and supplying fuel to the injectors. Changed filter. No spark at coil, so plugs don't play yet.
JA: Are you hoping to fix this yourself? What have you tried so far?
Customer: Yes. Suspect PCM, but not sure. Have replaced rotors, coil, CPS and tested voltages on TPS and a few other sensors. When I do the 5-turns on the ignition, I receive no error codes on the engine lamp.
JA: Anything else you think the mechanic should know?
Customer: I remove the PCM harness, and there was oxidation on a few pins. I cleaned, but no change. My next thought is to remove PCM, clean any oxidation, and re-solder the header.
Submitted: 3 months ago.
Category: Jeep
Expert:  rpmdiag replied 3 months ago.

Hi, welcome to Just Answer. I'm Ron and I will be helping you today.

We need to check the actual fuel pressure with a gauge to see if it is at specs if you have not checked it yet.

Also, check for a strong blue spark at the plugs with a spark tester while cranking it. let me know the results.

Thanks, Ron

Customer: replied 3 months ago.
Have not tested fuel pressure with a vague, but it appears normal when I manually click the relay. I've worked on the fuel system before.There is no spark at coil, so I'm wondering why you are asking about the spark plugs?
Expert:  rpmdiag replied 3 months ago.

You'll never know if you have enough pressure without testing it. No power to the ignition coil may be caused be the ignition switch.

I cover ALL the bases when I do diagnostics, it only took the one time to teach me that:)

Thanks again and please remember to rate me 5 stars and do keep this link in case you need me again later on.

Ron

Customer: replied 3 months ago.
Mir cranks, all lights come on, and I get voltages on the sensors when the ignition switch is on. Just jo start and no spark. So, do you still suspect the ignition switch?
Expert:  rpmdiag replied 3 months ago.

I'm in test mode right now, so I check ALL the possibilities. There is more than one wire coming out of the ignition switch, and YES, one of them controls ignition. We'll get to the bottom of this, but if my questions are annoying you, please let me know and I will opt out and let someone else take over.

Ron

Customer: replied 3 months ago.
No annoyance. It's diagnostics. will check these items and let you know.
Expert:  rpmdiag replied 3 months ago.

Very good.

Thanks again, Ron

Expert:  rpmdiag replied 3 months ago.

Also check this attachment I sent you. Not sure if you were here yet or not.

Ron

Expert:  rpmdiag replied 3 months ago.

Hi, I'm just following up with you to see if you have any more questions.
Thanks, Ron

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