Engine cutting out after warm up

@HDSlowride i ended up fixing mine. Same issues and was throwing the same parts at it. Ended up repairing a wire to the alternator that ran from the engine valve cover side loom down to the alternator. Looked like a factory splice that may have gave up after so many years.

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@HDSlowride

Were you able to figure this out?

My 92 YJ is now doing something similar. Instead of 5-10 minutes of running for it to become rough, it's about 30-40 minutes. The thing with mine is I notice it generally happens after hitting idle speed. I'll be driving home from work and I'll make it to the same general area when the roughness starts. If I keep it above roughly 1000 RPM, then it does not stutter/miss/backfire. Accelerating from a stop is when it's the absolute worst. When this first started happening, I would be able to accelerate through it, as the stutter/miss would only be momentary, but it has gotten progressively worse to the point that the jeep will start running so rough it dies at idle once it starts with the roughness.

What are the chances of this being a vacuum leak? A buddy of mine suggested that may be the culprit, but neither one of us are very familiar with the YJ's engine.
 
HDSlowride said:
Yeah, as far as the Air Intake Temperature sensor, I took it out and since it was pretty oil fouled from the PCV recirculating nasty air, I cleaned it good with carb and brake cleaner. I checked it with the ohm meter before I cleaned it and afterward as well. It was right on spec so felt no need to change it.
I did put a new coil in since there might have been a very slim chance it was breaking down once it went into closed loop. Of course, the new one didn't make any difference so I'll just have to wait now until I have more time to research and test for the problem.

My daily driver is an F350 dually Powerstroke so driving this 2.5L Jeep, even when it is running correctly, feels like I'm trying to coax a go-cart into going faster! Ha!
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Howdy,
Missing is generally a fuel injector or fuel pump issue. I am chasing and alternator problem... 92 YJ HO w/ 4.0l
 
I had the same symptoms. I purchased an "Inline spark checker light" from Harbor Freight for $4 to help troubleshoot the problem . Connect the light between the coil and distributor. When the engine starts missing check the light to see if it is blinking in time with the miss. I used longer spark plug wires so I could lay the light on the hood so I could watch it as I drove it down the street . This led me to a bad coil (it rattled when I shook it). If nothing else you can prove it's not an electrical problem for $4. Good luck
 
HDSlowride said:
I did put off my trip for a day or two just because I am still trying to get to the root cause of this issue. It definitely begins missing at the point the engine gets warm and the PCM shifts from Open Loop to Closed Loop fuel injection. It does the same exact thing every time. Runs ok for a few minutes while the engine is cold and then when it warms up and moves to a closed loop fuel injection sequence, it starts missing.
So I changed the MAP sensor and the oxygen sensor, thinking that one of these would be likely culprits for giving bad info to the PCM in closed loop. Did not help or change a thing.
I changed the fuel filter on the off chance that it may not be supplying enough flow to the fuel rail. Again, no change.
I put in a new crank position sensor. No change or improvement. When it starts missing after warm up, I can turn the key off for a few seconds and then back on and bump start it. This must trigger it back to open loop condition because it will run fine for just a couple minutes. Until the PCM realizes it is warmed up and tries going back to closed loop operation.
I do have a new coil to change out but have run out of time and it will have to wait until I get back from my trip, first of December.

After having changed out most all the items that I can think of that effect the info the PCM needs to operate correctly in closed loop operation, maybe it is the PCM after all. I'm sure someone, somewhere has experienced this identical issue!

I'll be checking in often to see what other advice comes and trying to sort through these issues. Thanks again for all the helpful advice.
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Help what ended up being wrong, I am going through the same thing
 
HDSlowride said:
Yeah, as far as the Air Intake Temperature sensor, I took it out and since it was pretty oil fouled from the PCV recirculating nasty air, I cleaned it good with carb and brake cleaner. I checked it with the ohm meter before I cleaned it and afterward as well. It was right on spec so felt no need to change it.
I did put a new coil in since there might have been a very slim chance it was breaking down once it went into closed loop. Of course, the new one didn't make any difference so I'll just have to wait now until I have more time to research and test for the problem.

My daily driver is an F350 dually Powerstroke so driving this 2.5L Jeep, even when it is running correctly, feels like I'm trying to coax a go-cart into going faster! Ha!
Click to expand...

Did you figure it out
 
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