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MJ running bad

patrick s

NAXJA Forum User
Location
palmer alaska
I have a 90 mj it is giveing me fits. I have checked all the sensors and they test good. The cps is reading .520 volts so it is good. The list is on #1 cyl. When running sounds like timing problem, back fires out exhaust and missing, cannot give it any throttle. I took a known good cps and slotted it to advance the timing. It ran a little better but not much, slotted it more and did run worse. The reason I slotted the cps is to check to see if the flex plate was wrong as some after market ones are bad. I am the 3rd owner and it was given to as no one could get it running right. It has the 4.0 engine and AW 4 trans, 231-case I get 10 in vacuum max, have 38psi fuel pressure. Any help would greatly appreciated.
 
You should make sure that your distributor is properly indexed and all plug wires are connected properly, etc. There is a great website that has a ton of awesome advice for Renix (87-90) Jeep 4.0L. Take a look and follow the suggestions there. However, it honestly sounds like an ignition/timing issue.

http://cruiser54.com/
 
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