Ok this is a WJ problem but I am posting it in here because it gets more traffic. I've had this 2002 with a 4.0 for about 2 years now. It seems to have a problem starting when warm (either when its sat 1-2 hours after running, or hasn't ran all day but is sitting in the sun), mostly starts fine when cold or hot. It either starts roughly, or starts then immediately dies. Fuel pump, spark plugs, coolant temp sensor, cam shaft sensor, crank shaft sensor, manifolds gasket have all been replaced to no avail. I don't know what to do next? Try a new starter? New fuel pressure regulator? It doesn't give me an engine light either. I'm getting tired of throwing parts at this thing. Any ideas?

 

It isn't the starter. Checking fuel pressure might be a good idea. I'd check for a leaking injector or two as well.

 

Try your battery.

 

Try this as a diagnostic tool. Called the poor man's prime.

Just turn the key to On but not to Start.
Turn it off after 5 seconds, and repeat.
THEN go to start and see what happens.

 

The battery has been changed as well. Radi, do you mean check for injectors dripping gas when the Jeep is off? So I should pull the rail with the injectors attached, turn the key to make the fuel pump come on and watch for drips?

 

^^I think I am going to do this test next.

 

I would pull the rail leaving everything attached, fuel lines, injectors etc and look to see if any injectors are still leaking BUT I wouldn't try doing it by turning the key with the rail loose. I would run the Jeep briefly, 10 seconds, turn it off, then pull the rail and check.

 

I checked the injectors and didn't see any drips.

 

Just curious. Are the gauges working OK? Might be an internet myth, but there are posts of a bad crank sensor causing goofy gauges. Some chance you got a bad one. Your symptoms sort of fit. You can also check it's connector, try un/re plugging it when it's messing up.

 

You mentioned trying a new starter. Is it cranking OK?

 

It has been having this problem since I bought it. Acting the same with the new crank sensor and the old one. I'm really starting to wonder if the flex plate is going bad. In the winter I would here a very loud ticking sound on cold days (didn't have many in tucson). I replaced the manifolds and throttle body gaskets and still heard the sound for a split second a couple times. We had a company van at work make a similar sound that had a bad flex plate but it did it constantly. Maybe for some reason my problems are affected by temperature, metal contracting and expanding. The starter seems to crank fine. That loud ticking sound and the starting problem got me thinking flex plate now. I was looking to see if it has an inspection cover but a lot of it seems covered, I might be able to in unbolt and pry up the bottom to have a look, I don't know, never inspected one before.

 

And no, the wacky gauges are not a myth at all. That happened on my 93 xj. It would randomly die when hot and the gauges would flip out.

 

Thanks! Yea, you have an inspection cover behind the pan.
On our old Renix Jeeps there was an issue of the CPS signal getting to the Puter', so bad the factory sold a bypass harness. (Mainly for 87-88 with a C-101 connector). Idk, I'd make sure that connecter looks pretty good. Maybe even try un/re plugging it while its messing up.

Mostly fine cold, or hot, just when it's warm. Good one! A chaffed harness only grounding at the "goldy-lox" spot?

 

Hello, not sure if this will help, but inspect your pcm. It shouls be behind the coolant bottle pass side fire wall. I have seen these rust out, water intrusion etc.... random poor running, stalling , hard start etc...
I have experienced this with both the 4.0 and the 4.7 l versions. dont just look at it. remove it and really have a good look.

 

It always starts. It's just that it stumbles a little, or something sounds off about the timing of the starting like it's not smooth, or it fires then dies immediately, but starts on the second crank. And it's usually when it's warm, starts perfect when it's hot, usually starts good when cold. And like I said there was that extremely loud ticking sound in the winter that sounded like a cracked flex plate.