This is kind of a pre emptive thread as I am working through some diagnostic stuff right now. Anyway will crank all day long but won't start unless you push the gas all the way to the floor. It will start, run rough a minute then smooth out and be ok until you shut it off again. Today is the warmest day we have had so far its about 75. About an hour before this started I had been driving it and it started and ran well for about 50 miles and several shut off and restarts today.

I do have spark. Full tune up was done two weeks ago. All NAPA premium parts and Champion copper plugs. New fuel filter in September (5000 miles ago) and the Throttle body and IAC was cleaned at that same time. Although I am giving it a once over now again even though it looks pretty good. Also, TPS was replaced with a MOPAR unit in January. In the back of my head I'm thinking fuel pump. I have had a rare stumble now and again when the motor was warm and generally the warmer it gets the worse it is but today it never did it. The times I have a had a fuel pressure gauge handy (which I don't have today) I could never recreate it making that diagnosis very hard. What else should I be looking at here?

 

Little update. Got the TB and IAC cleaned. No change. Tested the CPS it tested good. Kind of figured that since I had spark. Tested the TPS it was good. Nice clean sweep on the meter with no plateaus. So basically I'm down to fuel delivery I think. Don't have the money to rent a gauge until Wednesday so I guess I'm dead in the water till then.

Another little symptom I did notice though was when I did get it started and took it around the block it has a pretty bad hesitation when I give it gas. Once it recovers it goes ahead and accelerates and runs well. To me that points back to the fuel pump so I guess I'll start researching what the heck I need to do since I have a 1996 and they are nearly impossible to find from what I gather.

 

I agree with your thought, You need to check fuel pressure..

Just a thought ..

Ant...

 

A failing fuel pump can progressively get worse as it warms up.. But so can an ignition coil. The question is... Does this stumble feel like a hard sharp ignition misfire or more of a soft flutter which is more likely fuel volume related?

 

It feels more fluttery. Really like it's not getting fuel. Usually when it does it it's around 2000 rpms and just stops accelerating flutters for a few seconds if you push the gas harder it gets worse if you let off it goes away to probably not return again for a few days at least. Only does it on a warm engine usually over 50 degrees outside and on acceleration never idling.

After my last post I stopped messing with and it had the opportunity to completely cool. When out at dark to roll my windows up and it started right off the bat and ran good for a trip around the block with no stutter so definitely heat related somehow.

 

B4 throwing parts at it get it checked for codes. Unsure if key on key off method works on your year but its worth a try.....http://jeep-xj.info/HowtoECUcodes.htm

 

Only code it throws is for downstream o2 which it has been doing since I bought it.

 

Have you replaced the sensor yet ?

 

No. I know I need to but seems like most times when I go to do it something else happens. Power steering, battery, this deal. I was actually going to buy one when I got paid on Wednesday. I really doubt it will help this condition. It hasn't even been plugged in for who knows how long.

 

Been playing with it a little today trying to recreate it so when I go to take it in or get a hold of a gauge I can tell them exactly when it does it. Seems like its caused by heat definitely. Today it started and ran great. Even after a long drive. One thing about yesterdays driving was that the motor got a little warmer than normal in stop and go traffic. My aux fan isn't kicking on properly so it got up to maybe 230 during some of of the longer stops. So after I couldn't get it to do it I just let it sit and idle for an extended period and sure enough after a couple of cycles of letting it get hot and cooling it back off by kicking on the aux fan then heat back up again the problem started again. Not nearly as bad as yesterday but definitely the same issue.

 

Looks like it was the CPS. Had it changed out and yesterday it was hot and sunny drove it a while in town and never had the issue come back up. Now on to the next thing to fix.