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brownjeff, ASE Certified Technician
Category: Jeep
Satisfied Customers: 13886
Experience:  17 years experience, ASE certified, dealership certified, Service Manager for 15 years,
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2002 jeep liberty: 3.7 firing..cylinders

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I have a 2002 jeep liberty. 3.7 litre
it is burning dead rich. back firing and sooting the plugs up.
compression is fine on all cylinders.
fuel pressure is fine, however bleeds down slightly
sounds like the firing order is wrong. but the pcm controls that.

any ideas ?
Does the check engine light come on while driving and if so any codes?
Customer: replied 6 years ago.

THE light was on and then the battery went dead and erased them. got it started and ran for about 5 minuted and all it set was a o2 sensor code.

vehichle has no power and can hear back firing bad through intake plenum

A backfire through the intake is cause by a lean fuel mixture or timing. Since the fuel pressure is good most likely a timing issue. With no codes most likely a crank sensor failing but would need a scan tool to check the signal to determine this since it is still running.
Customer: replied 6 years ago.
I have a snap on scanner what will I look for in the data section ?
You will want to watch the sensor to see if putting out a signal. If you can watch a wave pattern that is even better. If the signal stops or the wave pattern is irregular the sensor needs replaced.
Customer: replied 6 years ago.
I just ran for about 7 minutes and no codes but the crank sensor is ranging anywhere from 7-250.... it did go to zero twice and never again ?
If going to zero then it is failing and will need to be replaced.
Customer: replied 6 years ago.

Do you mind if I replace and stay with you until I get it on in case that doesnt do it ?


If it fixes it I will kindly give tip

No worries......
Customer: replied 6 years ago.

I am unable to get the crank sensor until tomorrow. Is there anything else you can think of before I accept and sign off.

Also, if this doesnt fix it and I accept offer.... will I be charged again for asking you more info tomorrow ?



Can't think of anything else. The question will remain open even after you click ACCEPT and if you need to follow up tomorrow on this there is no additional charge as long as we are working on the same problem
Customer: replied 6 years ago.

I appreciate the fast response.... Hopefully I won't be speaking to you tomorrow.

Are you available tomorrow if needed ?



Yes I will be on line tomorrow if needed.
brownjeff and 4 other Jeep Specialists are ready to help you
Customer: replied 6 years ago.

can you help me with a follow up question on a 2002 liberty we worked on. I am still having issues and will gladly compensate if we can get this figured out.


you advised a crank sensor and that didnt do it.


Still no codes?
Customer: replied 6 years ago.
just codes that I created when unplugging coil packs to isolate cylinders. this is loading up so bad. no power and acts like firing order is just so wrong. Obviously controleed by pc.
A couple more ideas.....The cam sensor also controls the timing and if the timing chain has slop in it will alter the timing. You are describing a timing issue and would check these two items next.
Customer: replied 6 years ago.
this truck has 61k miles, would it be normal to have a timing chain issue ?
No a little low on miles for a timing chain issue.....but possible. Would try the cam sensor next
Customer: replied 6 years ago.

Ok I will get back with you... I appreciate all the help.


No worries......

Let me know