Cherokee_of_Tennessee

added this to the post above.

Turbo X_J

Find another mechanic.

Roler

OP, two of the most common causes of stalling/backfiring/rough running are a bad Crankshaft position sensor (CPS) or a bad camshaft sensor. Both can test ok, but be faulty. Your mech might have testd it, but I,d still wou.dreplace it. I tested my faulty one and it tested with contrasting results with leads placed differently as in good in one side, faulthy the other. Just to mention that. Especially the CPS will most likely need a replacement somewhere during its life in the XJ. A bad camsensor can give the same symptoms as well. Both sensors can be had for a reasonable price and far less $$ than a new ECU...

You replaced the fuel pump 3 years ago you said. Has fuel pressure been verified somewhere during this current issue?

'90Cherokee

I can't think of what the problem is, but some info: O2 sensors can't kill the engine or anywhere near. A working Catalytic will heat the outlet a lot, the more the better as far as the cat function goes, excessive heat from the cat is an engine issue not the cat. Bad gas (rare) should be an issue quickly after filling.

Cherokee_of_Tennessee

Yes, mechanic checked fuel pressure and said I have plenty of fuel pressure. He said I have more fuel pressure than he expected to see. I am thinking more and more I had two issues. The original issue was that it was hesitating, that got worse to the point where I got stranded on the side of the road about 3 weeks ago. I think the ECU was that problem. When I got it back from the shop it ran a little rough but never quit on me, and had great acceleration with no hesitation. I did not have any issues until I refilled with the bad gas. When they changed the cps and the injector, the rough idle smoothed out quite a bit, but still it stalled on the mechanic when he test drove it. Another thing to note, this week in Georgia while I had the bad gas in there, she was very very rough to start and idled like a diesel in the morning. This morning here in Tennessee, it is 25 degrees with a heavy frost. I went out to start her and warm her up. She started up and ran smooth as Tennessee whiskey spiked with molasses.

So I think the bad gas right after the ECU swap was a coincidence of bad luck. After I have now driven quite a bit on good gas, no more hesitation and she streaks like a scalded dog down the highway. But of course time will tell. I am cautiously very optimistic.

Roler

Hope that was it, keep us informed how things go.
Happy trails, mate.

Cherokee_of_Tennessee

Back to the freaking drawing board.

Hesitation and back fire again. Last night engine code "cylinder 1 misfire" showed up. Today during lunch it started hesitating and backfiring again. If I slipped it into neutral, I could rev the engine and it would run fine. As soon as I put it back in drive, it hesitated, back fired, rpms would drop to 100 or less and almost die.

Does ANYBODY have a freaking clue what could be wrong? I need some help cause this is my only vehicle.

Cherokee_of_Tennessee

As a last resort I drove to the jeep dealership. They don't think the ECU is bad again, but it could be bad since it is a remanufactured one. They said to check the distributor cap and rotor button. If that was ok they said to swap the ignition coil. I checked them and they looked fine. No corrosion or broken terminals. I swapped them anyway along with the ignition coil. This is my last attempt.

Cherokee_of_Tennessee

Just took it for a test drive. No go. Started hesitating and mis-firing so bad I thought it was going to throw a rod. I guess it will just have to go back to the damn shop.

'90Cherokee

I wish I could say I'm surprised. Rotor button and coil?!? That would affect all cylinders not just one. Let them fix it and don't pay for anything but whatever is the actual problem. They may fight you on it, you may have to pay the bill to get your car back. Ways to get refunded: use a credit card and file for a refund with them, call the BAR and see if they'll compel a refund, last resort is court.

Turbo X_J

What are you talking about? Court, charge back, stiff the shop, why?

Cherokee_of_Tennessee

So today as a last resort I took it back to the shop again. Only suggestion they had was to change the cam position sensor. Did that and drove back to work. on the way home it died again. Swapped out the fuel pump relay and auto shut down relay. I saw another forum that said these relays can cause the same issue. Did not make a difference. I was able to limp it into a gas station. Sat there for 10 min trying to get it to start. Finally it just started right up and ran like nothing ever happened. Drove it to the dealership and left it there. Hopefully they will fix it before my rental car contract runs out. I am at a loss here. Dealership says they don't have much hope. The only thing I can think of is that the PCM/ECU was replaced with a bad one. Dealership says you cant get a new one anymore, and all you can find are remanufactured ones. Anybody know where I can get a new one? Or does anyone know where a reputable remanufactured pcm can be had?

Cherokee_of_Tennessee

The only thing I have paid the mechanic shop for is the PCM/ECU. If the dealer finds that this is bad, then it is under warranty. And the mechanic shop bought it from the dealer that I took my jeep to tonight. I don't think the mechanic shop is trying to screw me. They just can't find the root cause, or the pcm they got from the dealer was DOA.

Roler

This sounds so very electrical.

1) The CPS was replaced, right? Do you know what brand was used?
2) when its not starting, does the fuel pump actually prime, as in: can you hear it in the back?

CCKen

What you are saying above makes me think that a component of the engine has chafed through a wire harness split loom and into the wires, either shorting a wire to ground or opening it when the engine torques from being in gear.

I think you should examine the wire harness looms for penetration and wiring damage within.

Start at the coil mount and work back towards the back of the head. The loom from the coil mount ground points carries important wires (see pic below) including the coil control wires. As the loom passes behind the distributor the Camshaft Position Sensor wires enters this loom. Examine this loom closely. There has been a case of the loom being penetrated at the valve cover stud bolt at the back right corner of the valve cover.

Follow the loom around to the left side of the valve cover. There has been cases of the #11 head bolt and/or the end of the fuel rail penetrating the loom. The loom in this area carries quite a few important wires on their way to the PCM. Also check the Crankshaft Position Sensor body harness wiring that goes into the fuel injector wiring manifold.

Edit: If you can get the engine running smoothly when in Neutral, wiggle the wiring harnesses I've described to see if anything responds.

G101 circuits: