Jeep misfiring, sputtering, and stalling

I have a 1993 XJ 4.0l that recently has started acting up. It started my last trip out wheeling, it would just shut off. Seem to happen much more going down hill. Generally would crank the normal amount of times and restart and sometimes would be fine, others would be badly misfiring and barely running. Giving it gas would not even do anything, it would continue to misfire. Then it would start running and be fine for a while, then randomly happen again. It also died twice driving on the street on the way home.

I figured that my problem is most likely the CPS/CKP (crankshaft) so I bought a new one from the dealer and replaced it a few days ago. Started right up on a test drive, but as I was driving up a hill and there was a little load on it, it started misfiring/sputtering. I parked it, turned it off and unplugged/replugged the CPS and it drove home fine. I drove it yesterday for a couple quick drives and it was fine. Drove it today to work and it was fine, but on the way home shortly after I left it started misfiring and popping out the exhaust under acceleration. Parked, unplugged/replugged the CPS again and it drove home fine.

Based upon what it's doing it seems like a bad CPS to me. However, I replaced it with a brand new one as I mentioned and it's still having problems. Before the new CPS it would just completely stall/shut off, now it misfires but still stays running. Seems weird to me that doing the old trick of unplugging/replugging the CPS seems to fix it for the time being and makes me lean towards issues with that still but it just seems weird considering it's a new OEM one.

Ideas? Thanks guys.

It's possible that the unplugging of the crank sensor is simply coincidental and that it may have started and run well for a while with just a restart. Should try that next time. I also would spray the crank sensor connector thoroughly and add a dab of dielectric grease and reconnect.

Does this problem ONLY occur when the engine is hot? Have you ever had it happen to a cold engine right after startup?

If it's only happening with a hot engine, then you are suffering from thermal (heat related) fail of a component. The #2 cause of that (#1 is crank sensor) is a faulty ignition coil. You could try testing it when hot, but if it's marginal, testing may not be conclusive.

Also sounds basic, but what is the condition of all tuneup hardware? Plugs, wires, cap, rotor, fuel filter?

Getting a fuel pressure reading would also be something to check as this is a process of elimination. At idle you should have 31 psi. Then disconnect the vacuum line leading to the regulator and the pressure should jump to approximately 39 psi.

Have you ever seen a check engine light? Even if the answer is now, I would check for any stored codes using either a code reader or the "key-on, key-off" technique shown below. Only takes 5 minutes.

Good luck and keep us updated!
--------------------------------------------------------------------

Retrieving OBD codes on the Jeep Cherokee (XJ)
OBD1 Models: 1991-1995
1) Start engine (if possible). Move transmission shift lever
through all positions, ending in Park. Turn A/C switch on and then off
(if equipped).
2) Turn engine off. Without starting engine again, turn
ignition on, off, on, off and on within 5 seconds. Record 2-digit
fault codes as displayed by flashing MIL.
3) For example, fault code 23 is displayed as flash, flash,
4-second pause, flash, flash, flash. After a slightly longer pause,
other codes stored are displayed in numerical order. When MIL begins
to flash fault codes, it cannot be stopped. Start over if count is
lost. Code 55 indicates end of fault code display.

birchlakeXJ said:

It's possible that the unplugging of the crank sensor is simply coincidental and that it may have started and run well for a while with just a restart. Should try that next time. I also would spray the crank sensor connector thoroughly and add a dab of dielectric grease and reconnect.

Click to expand...

I did try that once when it did it on the test drive. When it started misfiring I drove down the street until I could pull over, turned it off, and then tried to restart it once. It cranked about the normal amount of times, tried to start a little, but then kept cranking and didn't start. That's when I unplugged the CPS and then it started.

birchlakeXJ said:

Does this problem ONLY occur when the engine is hot? Have you ever had it happen to a cold engine right after startup?

If it's only happening with a hot engine, then you are suffering from thermal (heat related) fail of a component. The #2 cause of that (#1 is crank sensor) is a faulty ignition coil. You could try testing it when hot, but if it's marginal, testing may not be conclusive.

Click to expand...

Previously, every time has been with it hot. However, last night when I mentioned it did it on the way home from work it was cold. Jeep had sat for about 8 hours and it happened about 20-30 seconds after driving away.

birchlakeXJ said:

Also sounds basic, but what is the condition of all tuneup hardware? Plugs, wires, cap, rotor, fuel filter?

Click to expand...

Fuel filter is brand new, but the other stuff could use done, has been a few years. Has only ever had champion plugs and mopar plug wires but they're not real new.

birchlakeXJ said:

Getting a fuel pressure reading would also be something to check as this is a process of elimination. At idle you should have 31 psi. Then disconnect the vacuum line leading to the regulator and the pressure should jump to approximately 39 psi.

Click to expand...

I should probably check this.

birchlakeXJ said:

Have you ever seen a check engine light? Even if the answer is now, I would check for any stored codes using either a code reader or the "key-on, key-off" technique shown below. Only takes 5 minutes.

Click to expand...

I had checked this before the CPS and only had a recently disconnected battery. Just checked it today and it has nothing (goes straight to 55).


Thanks for all the help. Anymore insight is awesome!

I had the same issue with my 2000 xj and found the most unexpected fix. After replacing coil pail every common sensor except the O2 sensors which no codes for such were ever acknowledged during diagnostics. I suddenly remember that the problem only persist when I was pressing the accelerator. I was then prompted to a fuel sending problem, of which after removing the fuel tank, I discovered that the fuel filter was not secured onto the fuel pump assembly. I inspected the the filter and it was caked with deposits. I just replaced the whole assembly and it has been happy driving since. Hope this helps anyone experiencing this issue. ::flame:

Check the CPS wiring harness wires for damage. Moving them may be stopping a short for a time till engine and harness move and re-short it.