Dies after 10 or 15 minutes

[Eagle]

Since I started experiencing this problem last year, at least two or three other members here have posted about essentially the same issue. The truck is a stock 1988 4.0L, 5-speed. Runs great while it runs, but after 10 to fifteen minutes it just cuts out and dies. Once it dies, it WILL NOT restart. But if I sit on the side of the road for 45 minutes to an hour -- it fires right up and I can drive it home.

 

Problem is ... there isn't much of anywhere I want or need to go that's withing a 7-1/2 minute drive from my house, so the truck is basically useless. Something is obviously getting heat-soaked, and I don't have much of a clue where to start looking. The CPS is new, and the CPS harness by-pass has been installed. It could be a bad CPS, I guess, but the new one is a factory part and it's very rare for them to be bad.

 

Who else had this problem, and did you ever get it fixed/diagnosed?

[Geonovast]

How are the exhaust bolts? I remember seeing something on here about the exhaust manifold leaking really bad and heat-soaking the injectors.

[HOrnbrod]

Since I started experiencing this problem last year, at least two or three other members here have posted about essentially the same issue. The truck is a stock 1988 4.0L, 5-speed. Runs great while it runs, but after 10 to fifteen minutes it just cuts out and dies. Once it dies, it WILL NOT restart. But if I sit on the side of the road for 45 minutes to an hour -- it fires right up and I can drive it home.

 

Agree it sounds like a heat soak issue, but just what's heat soaking and dying is - :hmm: . That was pretty common problem in the later HOs, especially w. the 99+ intake heating up the #3 injector, and there were various heat shields addressed by various Mopar TSPs to "cure" this problem. A quick simple troubleshooting technique you might try would be to shim up the rear of your hood an inch or so just to see if the resulting lowering of the underhood temp might help make it better. At least this could make it certain that the engine cut off is in fact caused by excess heat buildup on a component. Is it worse in the summer Eagle?

[Pete M]

Got an inferred thermometer at your disposal?

[Eagle]

Don - The problem showed up last summer. I let it sit all winter so I don't know what would have happened in cold weather.

 

Pete - Nope

[Andy in Pa]

I'll tell you exactly what it is.... :brows:

 

There is a control unit UNDER the ignition coil on the pass side fender. It has two plugs that plug into it on the side that faces the engine. Remove the coil and remove this control unit and look at the filling epoxy on the underside of it (yes, its epoxy although it doesn't look like it). If there are ANY cracks in that epoxy, that is your problem. The electronics encased in that epoxy are not sealed from the outside elements any longer, and fail when the control unit becomes heat-soaked.

 

I had this EXACT same problem with my 87 MJ. It would run for approx. 10-15 minutes, then would die and NOT restart until it had cooled down. I replaced the CPS and the coil, and then went down to the Advanced Auto Parts below my house to investigate how much the pickup was for the distributor. I was talking to this young kid that works there about the problem (he has an MJ too, and had the same problem) and he told me about this control unit. He said exactly what I said above. If there are any cracks in the epoxy, the control unit is bad. I replaced it and problem solved!!!

 

I consider myself an expert in diagnosing these Jeeps.... and I learned something new that day!! :yes:

 

So try that, I bet it fixes your problem too.

[Akula69]

We had the same problem when we bought our MJ....in fact the old owner complained about it.

 

I found that it was caused by the engine block ground being loose at the block...when the engine heated up it expanded the bolt hole allowing it to lose contact.

[Pete M]

Pete - Nope

 

They don't cost much and can be a great help :thumbsup: (especially with cooling issues where you can just point at the radiator or coolant hose and know instantly where the blockage is)

[aemsee]

I'll tell you exactly what it is.... :brows:

 

There is a control unit UNDER the ignition coil on the pass side fender. It has two plugs that plug into it on the side that faces the engine. Remove the coil and remove this control unit and look at the filling epoxy on the underside of it (yes, its epoxy although it doesn't look like it). If there are ANY cracks in that epoxy, that is your problem. The electronics encased in that epoxy are not sealed from the outside elements any longer, and fail when the control unit becomes heat-soaked.

 

I had this EXACT same problem with my 87 MJ. It would run for approx. 10-15 minutes, then would die and NOT restart until it had cooled down. I replaced the CPS and the coil, and then went down to the Advanced Auto Parts below my house to investigate how much the pickup was for the distributor. I was talking to this young kid that works there about the problem (he has an MJ too, and had the same problem) and he told me about this control unit. He said exactly what I said above. If there are any cracks in the epoxy, the control unit is bad. I replaced it and problem solved!!!

 

I consider myself an expert in diagnosing these Jeeps.... and I learned something new that day!! :yes:

 

So try that, I bet it fixes your problem too.

 

 

:agree: Check this out. Was actually a fairly commom problem when I was working on the Renix stuff on a daily basis. I actually used to bring a bottle with water in it to cool off the coil/module assy to see if it would restart after it died.