Not sure what to do next trying to fix a bad idle issue. Having all the symptoms of a failing crank sensor like engine vibration, poor idle wont die but almost does when warmed up, under load at higher rpms it will skip or miss for a split second and continue accelerating, speedometer and mileage have stopped working entirely, engine is deffently holding back all together much like its misfiring but when cold started engine sounds good cannot hear or feel a miss until it has warmed up. The issue is constant it will skip or miss every time when warmed up. So here is what I've done so far with no luck have not fixed the problem.

93 XJ H.O. 4.0 AX-15 manual trans
New crankshaft position sensor
Champ copper spark plugs gapped 0.35
Spark plug wires
Distributor cap and rotor
New upstream 02 sensor
Check and repaired all the grounds I could find.
Cleaned all electrical plug connections
Checked fuel pump
New fuel filter
New fuel pressure regulator
Pulled fuel rail cleaned injectors and set with new O rings
Ran seafoam through the throttle and gas tank.

This problem started soon after I had changed my clutch, when reinstalling the cps I had forgotten to place the rubber shroud in the hole where the cps goes into the bell housing. Drove excellent for a week no issues then we had a very harsh freeze that happened very quickly, next morning the jeep would not start at all, cranked all day but no spark. I pulled the cps cleaned it and reinstalled with rubber shroud in place. At this point the jeep started right up but now had all the issues. So first thing got a new cps sensor and went from there with the rest of this goose chase. It's hard to decipher whether it's an electrical issue, grounding out, fuel delivery so I've tried to address all possibilities. Unfortunately I am about stumped and dont want to spend anymore money until I know I'm fixing the problem. Any ideas would be greatly appreciated thank you.

 

I'm having pretty much the exact same issue as you with my 93 XJ 4.0. I haven't done a new CPS yet or O2 sensor though. Were you ever able to figure out what was wrong with yours?

 

I have a 98 XJ, 4.0 auto, 2wd. Picked it up for free cause the previous owner couldn't figure out its major problem. I found that it had a broken spring due to carbon build up on plugs with a major MAJOR misfire and vibration. Intake valve spring. Fixed that problem and still a misfire but not as violent. I, too, have changed the CPS, cap and rotor, plugs(platinum), and checked all connections for continuity and ground. Everything checks out but still a misfire. I hope it's not my injectors not being able to distribute fuel properly. I am willing to dig deeper but dont really know where else to start testing. The parts cannon is loaded and ready. Just would like help to know where to start as well. I hope somebody is able to help us all!!?

 

Dutch, I wouldn't look at the O2 sensor yet. Check YouTube for some videos on testing a CPS. That's your first stop.

Curtis, Have you check he CAM Position Sensor? You also need to look at distributor bushings, and test your injectors.

 

Hi guys. I figured out my problem. Just to make sure this doesn't happen to anybody else out there, like my dumba$$, make sure the firing order is in proper order. I had 3 and 5 backwards hahaha🤪. Got it all fixed up. Good luck to you all still needing help.

 

There ya go!

There is a diagram floating around the Internet that shows an incorrect firing order. That may be the source of your problem. I have read that it came from a Chilton or Haynes manual.

The correct firing order is memorable (not that I agree with this, but it is memorable!):

36 is too old.
15 is too young.
24 is just right.


I kinda think 36 is just right, myself....