Engine cutting out after warm up

H

HDSlowride

New Member
Joined
Oct 22, 2021
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6
Location
Hartselle, Alabama
Just signed up to this forum so a complete newbie on here.
I just bought a 1993 Jeep YJ. Pretty stock looking powertrain. Previous owner had it for 4 years. I know not a bit of history on the vehicle. Odometer shows 196K miles. My brother drove it for a few minutes just around the guys neighborhood since he has an '89 YJ and more familiar with them. We trailered it home yesterday. I pressure washed some mud out from under it, greased all the zerks I could find. Sprayed PB blaster on every bolt I could get to.

Now the problem....engine runs fine while cold but after 5 to 6 miles as it warms up, it starts cutting out....sort of like it had bad gas all of a sudden. The warmer it gets, the worse it runs. Cutting out, sputtering, thought it was going to leave me stranded.
Thinking maybe that I got some water in the distributor, I popped it open when I made it back home and it cooled off. It was dry but had some buildup on the contact points in the cap. I headed to O'Reilly's and started my notebook. Put a new set of Champion spark plugs in it and a new distributor cap and rotor button. Plug wires looked ok. Also poured a can of Seafoam in the nearly full tank of gas just because.
Took it for another drive and it ran great for about 5 miles....it had good power for the 4 cyl and good throttle response. I thought I had fixed it. Then as it got warm it started the missing again....felt like it was falling off to two or three cylinders. It would idle pretty good but really struggled to hold power and gain rpm over 2000 rpm under a load. Again, the warmer it got, the worse it got. Limped it back home.
Coil breaking down as it warms up? Fuel pump issue? It's been a long, long time since I had to wrench on an engine...I'm as rusty as the lug nuts.

Any ideas from you experienced gear heads?
 
Is it throwing any codes? I was going to say something fuel related, but the fact it isn't doing it until the motor is at temp is weird.

I had to change out a crankshaft position sensor, because once my Jeep warmed up it would die. After it cooled for 5 minutes, I was able to start it back up no problem. But then it would die. I received a camshaft/crankshaft sensor code. I changed out the crankshaft pos sensor and no more problem.

It can be a mix of things. The sputtering sounds fuel related to me.
 
What I am seeing online, a camshaft position sensor can cause the issues you are describing. I believe there is a test for it. It is located in the distributor.
 
If you changed your cap, rotor and plugs, it might be a good idea to do wires as well. Are used to have a Chevy IROC- Z 28 that had massive problems with wires. Even when they look good. It’s just another thing you can rule out once they’ve been changed.
 
Still chasing this gremlin. My stock four banger starts easy, runs smooth when cold, good throttle response and pulls well. Until you get about 7 or 8 miles down the road. At first just a few sputters and misses, couple of pops and backfire. If I turn around when it starts doing this I am limping back in a much lower gear before I get home. It won't pull over 2K rpm once it starts cutting out. The warmer it gets, the worse the missing is.
I went to O'Reilly's and bought a throttle position sensor and changed it out. Didn't help at all. Repeat of the same thing. Runs good until it warms up then starts missing. I'm convinced it has to be electrical and interfering with firing but what do I know??? Ha.
So I've changed spark plugs, distributor cap and rotor button, and now TPS. I guess next I'll change the coil out.
Well, I am learning again after not wrenching on too much for many years. Noticed that it had no thermostat...don't know why. Like I say, have only had it a few days and no history is known to me. It looks as if most all of the original pollution control stuff is still in place. Mass air sensor voltage checked while running and it seems in normal range. The crank position sensor has been changed in the past (by its appearance) but these usually work, or don't work at all...correct?

Ideas appreciated, TIA
 
from what Ive read the CPS can do bad things like your having, for $25 might be worth a try. Also check and double check all your grounds. Unscrew,clean to bright metal and put back nice and snug. Resistance from bad grounds can make heat,heat makes for bad connections. Typical jeep issues. Also if there was no thermo I guess somebody was having overheating problems. They need a 195 to operate correctly and make the FI go into closed loop operations.
 
Trying to keep this thread up to date. I did remove the thermostat housing and was correct in that there was no thermostat. Cleaned everything really good and put in a new 195 degree thermostat. The heater does work after I coaxed the fan motor back to life. While I really thought that was the issue...It did not cure the engine miss after it warms up. Still the same...runs good cold for about 8-10 minutes and then starts missing and backfiring after it warms up.
I have a new coolant sensor that I will try next....then I think I will change the CPS. I also have a new coil that will go in next if these fail to improve. Unfortunately, I have another issue that will take me away from this hobby for about 5 weeks so hopefully I will be back on this thread in December. I don't want to abandon it as it may help someone else...assuming I eventually get to the bottom of it. Maybe the Powertrain Control Module (ECM) needs that repair that I have read about. Some guy (on ebay maybe) replaces a couple parts on the circuit board for $64 or something??
It still seems to me that something in a sensor circuit, or the ECM, is causing it to lose fire intermittently.
 
Well, I did have time to change out the coolant sensor. The old one that I took out did check correctly in the ohm range at room temperature (12.8K) although I did not bother to put it in hot water to see if the resistance changed as it should. I just put a new one in.
I also replaced the rubber elbow on the vacuum line from the fuel regulator to the throttle body because someone had wrapped some tape around it for some reason. Anyway, did those two things and the engine miss after it warms up is still there. Runs good...until it doesn't!
I did try one thing....after it warmed up good and started cutting out, I just turned the key off rolling slowly down the road. Left the engine off for maybe five seconds or so and then turned the key back off and popped the clutch to bump start it back off. It seemed as if it ran fine for a couple minutes before it started missing again. So that is something odd that I'll have to work out in the diagnosis.

Well...that will be about all on this thread until I return from a month long trip and get back to work on it in December. Again...if y'all think of anything that might help, drop a line here. I'll check in when I can and hoping someone will eventually say, "oh yeah, I know just what that is"!
 
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.
 
Frustrating to say the least. I believe the guys at "wrangler fix" can test it and see if the problem lies in the ECM. May be your best bet now. It do seem like once it hits closed loop which IIRC the engine needs to see at least 180 degrees the issue starts in.
 
PCM sounds like the next logical thing to change/test/replace etc. to me. Hate throwing parts at things but there really isn't much else it could be. It's pretty obvious the computer knows when to go into closed loop, so I'm sure the temp sensor is probably fine although I didn't see you mention it. But I would think it's working fine based on the PCM differentiating between closed and open loop. Only thing left really is the PCM.

As for where to get one, you might try eBay. WranglerFix came up with a PCM solution for the 05-06 TJs which have a very faulty design and pretty much all of them are affected by it by now which I imagine is why 05-06 are for sale more often than the others. Anyways, on YJ stuff WF is just buying and reselling for the most part, as far as I know. They might be doing some capacitor fixes but I think for the most part they are just distributing, not doing ground up rebuild type stuff like they do for the TJs. Still maybe worth a call to them, but last time I checked they wanted a lot more $ than the standard 2-300 PCMs cost at the time back then. This was probably 2 years ago when I looked. But if they are the only guy in town, then maybe worth what they're asking. You might try going and snagging some out of XJs instead, although with most XJs being 4.0, it might be tough to find the one you need.
 
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!
 
Ha...I had a 75 FJ40 with all the hot rodded parts on the 6. carb,header,distributor everything to be had back them. I got smoked by a friends non turbo diesel rabbit. :oops:
 
Did you ever figure out your issue? I am going through the same issue on my 95 2.5L. Just changed the crankshaft position sensor after a bunch of other ignition and fuel parts.
 
I seemed to have changed or checked about everything you have. Someone commented on a post on Facebook that it could be a pinched fuel line and to loosen the fuel cap. I may try this and see if it works. I just purchased my YJ and everything was running fine until recently possibly after I did my first fill up.
 
Well I think I found the issue with my YJ. I went through checking and cleaning connectors. I made sure distributor wasn’t cracked, rotor was good, and wires were in correct configuration. I found the harness on the drivers side above the PCM was caked with too much old dielectric grease and tried to clean it up the best I could. The problem I believe was actually a wire that came off the alternator. I’m not sure if it was broke or not making a good connection. But the green orange wire was sticking out. I soldiered it back together properly with added heat shrink. I finished tidying everything up and ran the Jeep for about 15 minutes at idle. It didn’t shut off, but I didn’t drive it down the road either.
 
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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Did you sort it mate? Mine doing exactly the same 🙈
 
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