This is going to be a long post to get all the info out. Thank to those who read it and reply.

1996, 4.0, 4x4, AW4

Last tuneup was done 1 year (12500 miles) ago. Plugs have been checked for gap and they look good, wires look good runs great and still descent gas mileage as long as it starts and stays running. I can usually figure stuff out by just getting on here but I am at my wits end with this one.

1st symptoms all intermittent. The hotter the weather the worse it got. This was about 1 month ago
Hard start
Wouldn't idle without giving throttle
died driving down the road

Took to mechanic because I was working 7 days a week. He changed out the crank sensor, changed the distributor, changed the cap, checked fuel pressure it checked out. Seemed to run better for 3 days then..

2nd symptoms all intermittent
hard start
Would die when putting in gear

Took back to mechanic. He started changing sensors. He has a cherokee and he started taking sensors off of his and putting them on mine. After the IAC, TPS, MAP, and a new ECU no change. His runs great with all my stuff on his.
After this I went through and refreshed the grounds again. I did this at the end of last summer but I figured I may as well give it a shot. After doing that it didn't act up again for 1 week then..


Hard start takes 3-4 cranks and long crank time both intermittent weather didn't seem to be an issue it was more when the truck got hot usually after sitting for a few minutes. IE stopping to get gas or running into a store for a few minutes.

Took back to mechanic and he changed all the sensors he changed the first time with new no change. (I didn't pay for any of that) At this point I changed all the mains. Not from 590 like I wanted but has to be better than what was on there. They were looking pretty sorry and my clamps were BAD. After doing this my AC worked better but my meter on my dash reads less. With a voltmeter at the battery it reads 13.8 and only falls to 13.5 with everything on while the dash meter reads 9. Not sure whats up with this. After this it seemed to be good (except for the dash meter) for 1 week then..

Hard starts 2-4 cranks and long cranks intermittent hotter weather its way worse. We had a couple of cool days in the mid 70s and I drove a lot it never missed a beat. Its hot today and had it die on me today when I was on the highway. first time thats happened since the beginning of this whole mess.

I have tried checking fuel pressure on my own but can never get it to act up when I have the gauge on. It always build right to 43 and stays there but as I said I haven't been able to recreate the issue with the gauge on.

Other maintenance that has been done to try and cure the issue but no changes are

Pulled and cleaned throttle body
Checked for Vacuum leaks changed most couplings whether they needed it or not. I didn't have a gauge though so everything was visual. I don't have any other idle or running problems usually caused by vacuum leaks.

So whats next? I'm sure I overlooked something easy that I should have checked from the get go but I'm at the end of my rope.

 

Check the wiring leading to the front O2 sensor. Then tend to rub against the manifold and melt in places cause erratic behavior. Give them a good look as I missed mine on the first look over. Hope this helps

 

"After this I went through and refreshed the grounds again. I did this at the end of last summer but I figured I may as well give it a shot. After doing that it didn't act up again for 1 week then.."

This vehicle ever been in a flood?

 

Not that I am aware of. I bought this vehicle a little over 2 years ago and have really had very little trouble out of it running wise. Little things here and there that you deal with with a 20 year old vehicle but nothing ever this persistent. I will check over the 02 sensor wiring as that was something I thought about as I typed this and then bruceb's comment peaked my interest. I have read about that causing issues just didn't really think about those reads in my troubleshooting thus far.

 

Spent the last 2 hours going through looking for bare wires, went through all the connections and unplugged and replugged several times to try and knock off any corrosion if any. And its was a no go. Didn't find any bad spots and after short drive get it hot it did the hard start and took 3 cranks to get it going.

 

I don't know if there is a way to test the ECU, but it sounds like it is failing or the connections to it have corroded.

 

I talked to my mechanic again today. Turns out he didn't replace the ECU. Had some confusion there I guess. he said that would be his next move if he was me so I'll try to track one down tomorrow.

 

Got the ECU replaced and it's a no go. I don't know I am at A loss right now.

 

Did the mechanic use a Mopar CPS? symptoms sure sound like it.

Maybe find another mechanic.

 

Yeah that's where I am at at this point.

 

So i found out some more stuff yesterday afternoon. He did not replace the CPS with a Mopar one it was from NAPA. I tested the CPS with the Ohms test and it reads about 2.5ohms which from what i read means it's bad and that it should read infinity resitance. Am I correct on this?

 

Is it OBD2? Do you have a scanner capable of live data & do you get a RPM signal while cranking?

 

It is OBDII but here is another fun part. The plug does not work. No idea what happened. Last time i had a light about 6 months ago it was working fine. Yesterday I plugged in to see if there was anything in the memory and its a no go. Don't know what happened there. No signal while cranking. As soon as it starts it up.

 

Im dead in the water again replaced the cps 3 times ready to clean the old one a give it a try worked once before. got the last one from rock auto

 

I am not sure, but I thin your obdII socket being dead is a great clue on to where to start looking for your electrical gremlin.
The following is from a post that member CCKen posted. These tests may help to find the root problem, if anything if all tests good, it eliminates them from the equation..


view entire post here https://www.cherokeeforum.com/f2/200...-start-213948/