Hi, I have acquired a 94 Cherokee, 4.0, auto. and it has a problem I have never seen before. It has this issue where sometimes it starts and runs great and other times it runs like crap. A few times it will be kinda in between and idle ok but not rev very good. Seems like you only have a one in ten chance of starting it and having it run good, other times it acts like the timing is off or getting too much fuel.
And this only happens at startup, if you start the car and it runs fine, nothing you do will make it miss a beat, if it starts up and runs like crap nothing you do will change it until you cut it off and try to start it again. Its all determined at startup for some reason, which is making it impossible to track down.

So far the previous owner has replaced every sensor that I can see, and other things I have tried to no avail, just off the top of my head I can think of the MAP, 02, IAC, Crank sensor (I also tried another more expensive new one, thought it worked but started it five minutes later only to have the same problem), a new distributor, coil wires and plugs. New Fuel pump, filter, pressure regulator, injectors. A new PCU, another wiring harness. I even replaced the starter and ignition switch, cleaned off all engine grounds cause the engine had been recently painted. Disconnected several sensors hoping it would throw it in limp mode, if it even has one (new to Jeeps, I only know Fords). Tried switching relays around, tying down wires, hitting things lol, nothing that I can see is definitely effecting it.
Nothing seems to change, there seems to be no pattern or rhyme to it at all, its all completely random.
Any help is greatly appreciated cause I'm completely lost on this one.

 

What brand sensors? Mopar is always best. I think you can use the key trick on the 94? Turn the key to RUN then OFF 3 times within 5 seconds, leaving it in RUN on the third. It should start flashing the CEL. Count the flashes. Codes are posted around here somewhere.

Here you go. The first list covers 91-97.
http://www.go.jeep-xj.info/HowtoECUcodes.htm

 

I Appreciate the reply, Not sure about the ones he changed but I just get whatever is available at Autozone. I Appreciate the reply, its showing no codes whatsoever aside from 55. The only codes I'm getting is the codes for sensors out of range when I try unplugging them.
Cleared the memory and get no check engine light while its running, even when its running like crap. Also when it does run smooth it sees to have a vibration or miss at low rpm from around 1000 to 1600 then it smooths out.

Seems odd and I'm not entirely sure since its so random but it almost seems like opening and shutting the doors give me a better change of a good startup..

What does the fuel pump ground to? Also is there any anti-theft switch somewhere on this year? I do know it seems to have a keyless entry because of the black bulb looking thing. Trying to narrow it down cause I keep thinking something somewhere is not grounding good or something critical at startup is not getting enough voltage.

 

Have you performed a compression test?
What's the fuel pressure is psi?

 

Bad O2 sensors should, in theory, always throw a code and a CEL.

They don't, and they can be random. You won't get good sensors from Autozone. You want NTK/NGK only.

And your suspicions about grounds are justified. Flaky grounds can do strange things.