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My first XJ and first post to NAXJA (Long post)

evan1395

NAXJA Forum User
Location
Paradise, CA
So my ZJ has burned down a few weeks ago. Tranny line blew and hit the hot exhaust. Went up like a roman candle. Its ok, I have always wanted a 5 speed 4.0 XJ anyway...AND I FOUND ONE!!!

Just picked this up a couple weeks ago. 1997, 4.0/AX15. 197k miles and runs amazing. Made the 50 mile trip home from the sellers house just fine. Drove it around town for a bit and noticed a fairly bad misfire about the first 15 minutes you drive it. Previous owner had installed new cap and rotor, copper autolite plugs, wires and ignition coil. Along with a new battery. I pulled the plugs, made sure they were gapped correctly, rerouted the plug wires, and checked the distributor for play or looseness. Everything ingition wise seems to be ok. I swapped out plugs with different ports and wires with different plugs. Even swapped around injectors....STILL has the misfire. And mind you. its still worse the first 15 minutes you drive it.
I pulled my OBD scanner out and got P0301. Misfire in cylinder 1. I checked the code prior to all this work and trouble shooting as described above. Took the XJ to my buddies shop and performed a compression test and leakdown test. The #1 cylinder was around 110-115lbs. While the other five were at a perfect 150. The leakdown test only showed 10% on the problem cylinder. So I took the jeep home and opened the hood today.
I had my jeep idling with the hood open, started messing around with the injectors, ensuring the clips and injectors were all seated properly just for the hell of it. I pushed down on the #1 injector connector and wiggled the wires a certain way and the misfire stopped. Diminished completely, GONE. I kept my hand on it for a good 20 seconds just to make sure what i had done had really stopped the misfire. I took my hand off and it immediately started back up. So i figured, id go buy a new injector pigtail and solder it on. That just HAS to be the problem. Well i went and spent the $6 on a new pigtail and it is STILL misfiring. So i got to thinking that maybe the pressure i induced on the injector, was more of a O-ring problem. Like maybe the O-ring was bad and it was sucking in air. And possibly the pressure i put on the injector just helped seat the o ring and make it stop misfiring. Sooooo, I went out and bought new O rings today, installed all 6....and im STILL getting the misfire.
I just drove to the store to grab a brewski. Again, it was misfiring terribly when cold. Made the 15 minute/5 mile round trip, pulled into my driveway and the misfire is almost non existent. The previous owner has straight piped this (no muffler, but still has a cat and 02 sensor). So the misfires and louder exhaust idle is somewhat hard to tell apart. I put my hand to the tailpipe and no suck back. Atleast not anything noticeable.

At this point i am stumped. The only thing that REALLY stopped my misfire for as long as it did...was when i had been fooling around with my #1 injector. Idk if it was the way i positioned the pigtail wires...or the way I had settled the injector itself.
Help!!!
 
Give it a little more time... 2 hours isn't much.

Did you try a new injector?
 
To test you can swap injectors between two cylinders and see if the miss fire follows. Test costs nothing.
Tough now would be a good time to get the upgraded injectors if that's in your plans.
 
Swapping around injectors is the easiest way to eliminate it as a culprit. If it does not cure the problem, I believe the injector harness is a one-piece unit and can be pulled from another XJ and swapped in.

I had a similar problem but with a coil pack on a 5.4L Ford. It was a combination of a loose fit (solved with a new coil pack) and a brittle wiring harness for coil pack (solved with a junkyard re-solder).
 
Are you sure the injector is sealed? Sounds like pushing down on the injector stopped your issue and your compression on that cylinder is low. Not sure exactly how it could leak compression that way but it certainly sounds like an idea. I'd get new o-rings but a quick test could be some dielectric grease on the current o-ring and giving it a run. Do you smell gas under the hood too?
 
I swapped injectors. The miss stayed on cylinder one. The CEL has not come back on yet since installing the new injector pigtail. However the missfire is still there. Which is weird, because the CEL would pop right back on before i swapped the new connector on for #1 injector.
I just installed new O-Rings yesterday. No leaks. And yeah, there is a verrry faint smell of gas under the hood while its running.
 
I cleaned out a bunch of crap from all the matinf surfaces. Just took it for a drive and the CEL popped back on :/
Im so effin lost at this point.
 
I would double check your wiring with a noid light. Obviously if moving the wiring around there causes the problem to come and go, there is a problem. The compression is not low enough to miss like you describe.
 
I would double check your wiring with a noid light. Obviously if moving the wiring around there causes the problem to come and go, there is a problem. The compression is not low enough to miss like you describe.

Yeah, I keep being told that of ot was a burnt/stuck valve or even a head problem, that the compression would be a whole lot lower than what it is now. What is a noid light?
 
Well i checked the injector pigtail for #1. Noid light and mulitmeter both showed it was good. Guess its time to buy some starter fluid and check for intake leaks.
Could a bad cat/02 sensor cause a cylinder 1 misfire?
 
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