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Brad
Brad, Jeep Dealership Tech
Category: Jeep
Satisfied Customers: 3419
Experience:  16 Yrs Chrysler/Dodge/Jeep. ASE Master (L-1) Certified
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1995 jeep: cylinders..pcm..ecm..coil,check timing.still

Customer Question

Have a 1995 jeep grand,misfiring and backfiring,so bad has blowen muffer apart,did compresson test on all cylinders at 150psi each,replaced spark plugs,pcm or ecm,dist. cap,rotor button,pick-up in the dist.,ign. coil,check timing.still back firing.running like on two cylinders.
Submitted: 2 years ago.
Category: Jeep
Expert:  Brad replied 2 years ago.

Brad :

Hello welcome to JustAnswer, My name is XXXX XXX I will be assisting you

Brad :

Have you checked fuel psi?

Brad :

Also is the check engine light on?

Customer :

no,no codes

Brad :

Do you have a fuel psi guage to check the fuel psi?

Customer :

yes,i did. at 55 psi

Brad :

Does it misfire all the time?

Customer :

yes,seem like something is cutting out the coil,checked the wire going to the pcm that controls the ground for coil and it has voltage on it.

Brad :

The PCM controls the ground pluse width to coil.. ASD Relay provides 12v.. If there is voltage on wire from PCM there is something wrong..

Customer :

going by my wiring diagram it should be the ground right?

Customer :

checked the wiring at the coil

Customer :

one has 14 volts on it and the other has about 7 volts

Customer :

the other one should be ground?

Brad :

[IMAGE][SRC][/SRC][ALT]zj604254[/ALT][WIDTH]100[/WIDTH][HEIGHT]100[/HEIGHT][STYLE][/STYLE][/IMAGE]

Customer :

so thats why i checked it at the pcm. yet,it still has voltage on it

Brad :

If the Gray and white wire has voltage on it.. The PCM is faulty

Customer :

replaced the pcm

Brad :

The new one is fauty then, or the wire is shorted to voltage somewhere..

Customer :

k,so can i cut that wire at the coil,run a new one to pcm?

Brad :

You can try that... or just cut the wire at PCM and make sure it has ground coming out of PCM..

Customer :

k,let me try that

Brad :

Ok post back your findings and we can go from there.

Expert:  Brad replied 2 years ago.
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Customer: replied 2 years ago.
cut wire at pcm,it would ground when spinnig key over
Expert:  Brad replied 2 years ago.
Correct!!! When you are spinning engine over it will be flashing the test light if you have it clipped to the Positive battery terminal....
Customer: replied 2 years ago.
yes,but found out its a 1994,does that make a big differents?
Expert:  Brad replied 2 years ago.
The PCM still sends ground to the coil.. The wire may be a different color..
Customer: replied 2 years ago.
still cant figure out whats happening,the pcm ground for the coil,gounds like it should when disconnected from coil.yet,when hook to coil it has some voltage on it,replaced coil again,still same thing.
Expert:  Brad replied 2 years ago.
Try this: Disconnect the coil and on the ground coming from the PCM, hook up a fog light to positive side of battery and see if it lights it bright.... That will see if it's a strong ground coming from PCM.... It sounds like under a load the PCM can't provide a strong ground.... Post back results

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