1990 Cherokee 4.0 backfire misfire help. - Pirate4x4.Com : 4x4 and Off-Road Forum
 
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Old 05-13-2009, 12:06 PM   #1 (permalink)
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1990 Cherokee 4.0 backfire misfire help.

Sorry for the long post but Iím about to scrap this if I canít fix it.

I have a 1990 Cherokee Limited with a 4.0, automatic with 130k miles. And I am having problem with it backfiring when I let off the gas when driving. If I rev it up in neutral it also hesitates and misfires/shakes badly. The fuel economy is also bad, I was getting about 16mpg now Iím getting 12mpg.

This is a list of what I have replaced recently.
Exhaust, from the manifold back including new converter.
O2 sensor
Intake/Exhaust manifold gasket.
Fuel filter
New distributor, distributor cap, plugs, wires
Water pump
Radiator
Harmonic balancer pulley.

I replaced the distributor because the old one was oscillating badly when running. The remanufactured one I put in still oscillates but not nearly as bad. I just got another remanufactured distributor to replace the other one thinking thatís the problem but havenít installed it yet.

Any and all help is much appreciated, Brad
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Old 05-13-2009, 12:22 PM   #2 (permalink)
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Sorry for posting in the wrong section...
Fixed
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Old 05-13-2009, 02:44 PM   #3 (permalink)
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Check your timing.
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Old 05-13-2009, 02:58 PM   #4 (permalink)
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Is there a way to adjust it? I put the distributor in by the book about 10 times because I thought it was off a little. It will only start in one position and how the distributor mounts how do you adjust it?
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Old 05-13-2009, 03:08 PM   #5 (permalink)
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Loosen the bolt that holds it down and try to rotate it while the jeep is running. See what happends.
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Old 05-13-2009, 03:09 PM   #6 (permalink)
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Check for leaks @ yer manifolg gaskets too.
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Old 05-13-2009, 04:00 PM   #7 (permalink)
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Loosen the bolt that holds it down and try to rotate it while the jeep is running. See what happends.
You can't rotate it. It has a U formed into the distributor that the bolt goes through. I tried taking the bolt out and holding the distributor in by hand, but when you try to start it pushes it out. Is a bent distributor a common thing on the 4.0?
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Old 05-13-2009, 04:03 PM   #8 (permalink)
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Check for leaks @ yer manifolg gaskets too.
I just replaced it. I sprayed carb cleaner everywhere looking for a vacuum leak and no change in engine noise
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Old 05-13-2009, 04:24 PM   #9 (permalink)
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Are you sure the motor is good? No burnt valves or broken springs etc....
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Old 05-13-2009, 09:13 PM   #10 (permalink)
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Are you sure the motor is good? No burnt valves or broken springs etc....
I'm not sure how do I test for that?
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Old 05-15-2009, 11:50 AM   #11 (permalink)
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I finally got it running right. I put another remanufactured distributor in and it runs perfect. What a PITA all the stuff I replaced and it was a bad new distributor.

The new distributor still oscillates when itís running. What would cause this?
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Old 05-16-2009, 09:49 PM   #12 (permalink)
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I finally got it running right. I put another remanufactured distributor in and it runs perfect. What a PITA all the stuff I replaced and it was a bad new distributor.

The new distributor still oscillates when itís running. What would cause this?
A video would help with this one.
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