Need some help - misfire/no start when warm

Hey guys. Been lurking this forum for a while, but I just signed up. Been trying to figure out an issue for a while, and after doing tons of searching, I'm stumped. I've seen some good advice on here, so I thought I'd ask you guys.

So, I've got a problem thats getting worse and worse with my jeep. It really only seems to be an issue when wheeling. She starts up fine when the engine is cold, and usually even when its warm. Lately though, when I'm out wheeling and stop for a beer or whatever, I go to start it up, and sometimes she'll just crank and crank with no start. And when it does start, its got a pretty bad misfire.

And to make things more confusing, after one instance where it just didnt want to start, I disconnected the battery, touched the negative to metal to drain the ecu, reconnected the battery, and it started up, no issues.

It reminds me of the issues I had with the Crank Position Sensor, but I replaced that less than a year ago, with a genuine mopar part.

Any ideas?

I would start with thinking about what caused the first CPS to go bad and consider the new one is also now bad.

I had a pretty bad transmission fluid leak that was dumping fluid onto the CPS, ho restarts were as you describe. Once it say and the fluid seemed to drain away it acted normal. Maybe next time it doesn't want to start check around for fluid leaks around the CPS and its electrical connection.

Also, others will ask, what your year make model info are to better help...

iwannadie said:

I would start with thinking about what caused the first CPS to go bad and consider the new one is also now bad.

I had a pretty bad transmission fluid leak that was dumping fluid onto the CPS, ho restarts were as you describe. Once it say and the fluid seemed to drain away it acted normal. Maybe next time it doesn't want to start check around for fluid leaks around the CPS and its electrical connection.

Also, others will ask, what your year make model info are to better help...

Click to expand...

Ah, my mistake. Its a 96 XJ, 4.0L, AW4 trans. As far as the CPS, nothing was leaking on it. I was having some problems, and researching them pointed to it. I was under the impression that its somewhat common for them to fail, based on what I read. It fixed the issues I was having at the time.

Seen on U-Tube, when checking your CPS be sure that its magnetic strength is there. If it is weak probably time to replace it.

Would an OEM unit go bad in less than a year?

When your Jeep will crank and crank, but will not start after sitting for a while; try taking a small amount of water and pouring on the CPS. The heat can affect a CPS and the water will cool it enough for it to start.
During an event several years ago there was a Jeep that would crank, but not restart when the engine was warm. I suggested he pour a little water on the CPS; then try again.
Restarted first try....., but I advised him this would only work a few more times before the CPS would fail permanently.

I was doing some work under the hood today (new iac valve, map sensor, and tps, as well as taking care of a couple vacuum leaks I found), when I noticed fuel stains on the intake manifold under 3 injectors. Any chance this could be causing the problem?