Well, I've been dealing with a Demon of a Jeep and I'm on the Jeepforum, with lots of help, but for some reason I can't figure this Jeep out...


It's a 1995 CG w/4.0 4x2. I've replaced the CPS, cleaned ALL the grounds (made them shiny), Removed the VTSS module from behind the glove box (yes it ran for week with it off), jumped the drivers door alarm wire, new plugs/wires/cap & rotor, replaced the IGN coil, had the ECU & CAPS repaired, timed it to the "T", etc ...

What it's doing is it stalls about 10-45 minutes into it running even when idling, it usually won't start till it cools down, and LATELY it won't even stay running and stalls right away...

I'm thinking there's a dead short somewhere in the Jeep harness, like maybe the Gremlins love the wiring harness taste.

Maybe when I do get it running, i'll shake the wires all over and see if it dies, if it does, then the short is in that general area.

ANY help would be great!!! As this Jeep has made me loose sleep trying to figure it out.

 

The cam sensor (pickup coil) will fail when it gets hot and won't restart until it cools down. Have you replaced that?

 

How is the fuel pressure?

 

+1 on the cps

 

Just a thought but could it be fuel pump getting hot and shutting down

 

It can, but not likely. Once a fuel pump craps out it usually stays crapped out.

 

Yes, I've replaced the CPS. They either work or don't work as I've seen. Fuel pump, might be going bad? or maybe the fuel filter is clogged.

 

I've also replaced the cam sensor, pick up coil, distributor, all wires, cap, plugs, etc. I also replaced the O2 sensor, had a new exhaust manifold put in (was cracked like all 4.0's)... Something else is up... I was told by another mechanic again it MIGHT be the engine harness that has a short somewhere.....

 

Easy check. When it dies shoot some starting fluid in the intake a try starting it. If it fires off and runs for a moment then it is the fuel pump. If it won't even try to run then its the can sensor or some other ignition related issue.

 

Doing some more research, I think some people have had issues with the Ignition piece in the steering column. I guess sometimes the contacts get worn or don't make contact and then it seems like the key is in the "off" position.

 

Couldn't hurt to check it out.

 

Apparently you are satisfied with the fuel pressure?

 

I have to get the Jeep over to my house. It's stuck somewhere else... I will check the fuel pressure... I forgot how much it's supposed to be, 40 psi?

 

After it sits overnight, turn the key on while watching the gauge, it should go right up to 50 after the pump runs 3 seconds.
running also around 50. should hold pressure after shut off not go less than 25 lbs after a certain number of minutes which i forget ..

 

Well, there you go. If it fires or starts with fuel of some sort in the intake, you've got spark and the problem is fuel. If it doesn't fire, you've got no spark. If the ASD relay isn't energized, you get neither.

The way this works is when you turn on the key, the PCM energizes the fuel pump to charge the fuel rail. When you start cranking, the crank sensor (CPS) tells the PCM that the crankshaft is actually turning. Then the PCM energizes the ASD relay and the fuel pump relay. The ASD turns on the ignition and the fuel injector circuits. The reason for so many relays is the PCM operates on 5 volts and everything it controls is on 12 volt circuits. Oh...wait! I think the injectors are 5 volt, but I'm not sure.

Even though you changed the CPS, the wiring may not be good. It's only supplied with 5 volts and connections must be perfect. It's possible the ASD relay is no good. That you can check by substituting a headlight relay.