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Dies when hot

at2_tweak

NAXJA Forum User
Location
Porterville, Ca
I've been having this problem on the rig where it suddenly dies when I take my foot of the gas. I've got a 96 4.0, auto and basically stock. The problem I have seems to happen when the engine is hot or has been under a load for a while, especially when driving uphill. It also tends to happen sooner when the weather is hot, kind of like the engine gets hotter quicker and this causes the jeep to die. After it dies and I let it sit for a while, sometimes up to an hour, it will re-start and run fine for a while until I put it under a load again and let off the gas, then it's dead again. Real friggin annoying to say the least. I've shot a little starting fluid in there and it will start up for a second then die again, so I don't think it's getting fuel. I'm trying to determine if it's the fuel pump going out or if the CPS is toast. The fuel pump isn't making any whiny noises so there's nothing really pointing towards that but who knows. Any suggestions?
 
Test both the fuel pump and the CPS. Inspect the fuel filter. Replace whichever does not pass testing.
 
Yea I failed to mention that I had covered those bases already. I've changed the fuel filter, tested the CPS and the fuel pump already, and they check good. The problem is that I've tested the parts while the Jeep is sitting in the driveway and not when this problem is happening. I'm thinking the CPS is having some type of thermal failure after it gets hot, but I'm not sure and I hate just throwing parts at these gripes and hoping for the best. Buuut I guess in this instance I'm just going to have to do it and hope for the best. Now I'm just wondering which part to shotgun with first.
 
If it ONLY happens when you are not on the gas pedal, two possibilities come to mind.

1. The "throttle position sensor" is a suspect.

2. A marginal battery. And yes, you can have a battery that is plenty strong enough to start the engine, but marginal enough to give the engine management system fits and create stalling at idle. In fact, stalling is a very common symptom of a battery going south. Have your battery "load tested". Any parts store will do this for you for free.
 
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You say it only happens under load or when its hot... Have you checked where your CPS is ran? Mine was ran right beside the exhaust manifold (dumbass PO) and caused it to malfunction when the jeep got hot.
 
The CPS will fail when it gets too hot. Sometimes once they cool down, they will function again, sometimes not. IMO, that would be the #1 culprit in this situation.
 
I keep going back to the fact that it fails ONLY at idle. That really does not sound like a crank sensor to me. If it was the crank sensor (and yes, they can suffer thermal failure) you would see it at all different situations like under throttle, cruising, etc. Get that battery load tested. And be sure that the charging system is keeping that battery juiced to prevent stalling.
 
I keep reading the part that it happens sooner on warmer days, and always right after he was loading the engine (higher exhaust temps). What he writes is exactly the same issue/symptoms I had when my exhaust manifold had a tiny crack and putting heat right onto the CPS. Once it cooled down over a period of 20-30 minutes, it would run fine until the unit got too hot again.

Could be several things. OP will have to test.
 
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