2000 4.0 TJ misfire issues

wheelnmac

wheelnmac

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Mar 22, 2020
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Granada Hills, California
So here is the long version. I was on my way to the desert with my trailer in tow and the Jeep quit on a hill. Got it towed home and replaced the crankshaft position sensor. Nothing. Drained the fuel and replaced the pump. Bingo. Fast forward to last week. The jeep has been sitting. Starting it once a week. Serviced it last weekend did fresh batteries and went to go do a smog.

None of the systems were ready and it was codes "pending" P300, 301, and 306 but no check engine light. Went home and changed plugs. I had E3's in it and I had a second set in the garage so that's what I put back in it. Yes I fell for the better fuel mileage crap. 12 miles into my drive the next morning, check engine light. Same codes. Went home, Autolite xp985's went in. 30 miles into my drive the next day engine light and its a P306. By the time I get home its a 300 and 301 along with 306. Hello Autozone and a new coil pack goes in. Had a new PCM, I put it in. 1 can of SeaFoam in to the intake manifold. SeaFoam in the tank.

Almost 30 miles the next day and I get P300, 302 and 305. Yay new cylinders. Now I put regular old Chapions in. #412 to be exact. 50 miles, no light. Pull in the driveway and plug in, "pending" P306, CAT ready and O2 ready, EVAP is not. Replaced the #6 injector. This morning, not even 30 miles into my drive and I get the light. P306. I'm considering putting the old coil pack back on and going for a drive later unless someone thinks I should try something else. I'm at a loss guys. HELP!
 
For what it's worth, almost any replacement part Autozone sells is 100% Chinese garbage. I wouldn't trust those coil packs, the only ones I would trust are the OE Mopar ones, as these things are known to reject almost any sensor other than OE Mopar sensors.

I'm assuming you also didn't use a Mopar replacement crankshaft position sensor? If so, that's another well known issue.
 
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Chris said:
For what it's worth, almost any replacement part Autozone sells is 100% Chinese garbage. I wouldn't trust those coil packs, the only ones I would trust are the OE Mopar ones, as these things are known to reject almost any sensor other than OE Mopar sensors.

I'm assuming you also didn't use a Mopar replacement crankshaft position sensor? If so, that's another well known issue.
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Closest one is Henderson, Nv. Unless I still have my original.
 
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Put the newer coil pack back in. Ran great in the driveway for like 5 minutes. Straight to running like crap after I revved it up. P0304 misfire. I'm lost. I'm confused. I wish I had a 4B Cummings in it. Diesel is so much easier.
 
I suggest you check your cylinder head far a crack. Had the same issues a while back and that’s what it turned out to be.
 
Just a suggestion. I had similar issues that turned out to be a cracked head. Hope your head is not cracked. First my misfire started with CEL PO306. Changed #6 fuel injector and coil pack. Jeep would start up and run good and misfire would start after engine would warm up. Started getting CEL PO300, PO303 and 304. Changed O2 sensors (NTK installed ) spark plugs and just about every other sensor with genuine Mopar sensors. Still would misfire once engine would reach operating temperature. Changed cylinder head. Problem solved.
 
por212 said:
Just a suggestion. I had similar issues that turned out to be a cracked head. Hope your head is not cracked. First my misfire started with CEL PO306. Changed #6 fuel injector and coil pack. Jeep would start up and run good and misfire would start after engine would warm up. Started getting CEL PO300, PO303 and 304. Changed O2 sensors (NTK installed ) spark plugs and just about every other sensor with genuine Mopar sensors. Still would misfire once engine would reach operating temperature. Changed cylinder head. Problem solved.
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So I just found out about the 0331 head. I have the 0331 head. Just did a compression test. 145psi across the board. On my way to the dealer. They have an OEM coil pack. Gonna install that with another new set of plugs from them. Fingers crossed. Did you do a compression test?
 
UPDATE..............new plugs from the dealer and a new in box coil pack. Just drove for about 40 miles. No codes. I've gotten codes from before even leaving the driveway all the way up to about 35 miles. Stopped and topped off on the way back home. No codes again. Taking it for a drive in the morning for about 50 miles and hopefully that will be enough for the CAT and O2's to get ready for smog. I don't need EVAP to be ready in CA. I'll have my reader with me so we will see.
 
TJ2 said:
Starting to develop a love-hate relationship.
I am lost of words.
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I feel you. I wanted to put a rag in the filler neck and light it. I'm the original owner.This is the first major issue. I'm the only one that's ever been under the hood so the learning experience with OEM parts has been an expensive one.
 
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