kevinz

I have a 96 Cherokee with the 4.0/AW4/4x4 (231). Here lately, it has bee having an intermittent problem where it will stumble and backfire real bad after driving it for a bit. I replaced the wires, plugs, cap, and rotor since they looked like they hadn't been done in years (bad carbon on the terminals + no electrodes on plugs = bad juju.) That has helped it run better, BUT it will still occasionally do this. Seems to occur around 2k-3k RPMs but again, it DOES NOT happen all the time.

Since it is obvious to me that regular maintenance has been a second thought for previous owners with the Jeep, and it has almost 201,000 miles on it, I was thinking that maybe my crank sensor is about to retire and head to Florida. Anyone else ever have this problem? Was it the CPS? I was also thinking the coil, but I need to catch it doing it again so I can check both with my voltmeter.

lemansguy

i had a stumbling problem with mine, just like yours wasnt all the time, didnt throw a code for 2 weeks. finally ended up being the rear O2 sensor.

kevinz

Just thought I'd post and update. Changed the fuel filter and the pre-cat 02 sensor, and the problem still exists, it did it tonight after the Jeep was warmed up and I floored it from a complete stop. This time I had my Snap-On scanner hooked to it and saw that the crankshaft and camshaft sensors lost sync when this happened. It idled fine and revved fine at idle, just when warm and the gas is mashed I lost sync between those two sensors.

Anyone have that happen before? What would cause them to lose sync and my engine to act like this? Or is something else going on causing the problem and I'm losing sync cuz of it? HELP!

Turbo X_J

Do you have the ability to capture live data? What happened to the TPS voltage when the crank/cam sensors went south?

kevinz

I do not know; I can look at the scanner for that info and check. I looked at the TPS waveform on a scope last night and it looked good. This is driving me nuts; it does it usually when warmed up and I hear that the 96-98ish PCMs have an issue where they lose the cam/crank sensor sync when warm, and if I could just figure out why and fix it we'd be in business!

AVjeeper

Fuel pump? What's the fuel pressure on the fuel rail? Symptoms are similar to low fuel pressure.

X1994J

I agree.. when my fuel pump went out it took me a while to figure out what it was, always ran great until the pump got hot. So at idle fuel pressure always read good. Can you put a fuel pressure gauge on it and tape it to the wind shield so you can watch it? Thats what I ended up doing.

kevinz

I do have a fuel pressure gauge, dunno if the hose is long enough to be taped up somewhere to watch, but i can hook it up and let the jeep warm up, see what it does. The fuel filter looked like it hadn't been changed in forever and the fuel that came out of it was nasty, so i wonder if maybe that restricted filter damaged the pump