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Intermittent miss

Austcord

NAXJA Forum User
Location
Idaho
Okay so, I am absolutely stumped. I need some advice. I just recently purchased another 96 xj to fix and sell. Here's the background, it has 209k miles on it, it is the 4.0 motor, automatic trans. I purchased it from the original owner. It had been overheated so I picked it up next to nothing, pulled the head, checked the cylinders, did a head gasket. I have great compression now. The thing will not run smooth to save my life. I cannot figure it out and I'm about ready to haul it to the scrap yard. I have changed the CKPS, the distributor, rotor, plugs, wires, alternator, unplugged the O2 sensors and tried it, swapped cam sensors with my running 96, tested all the injectors, tested IAC, MAF, TPS, I have no idea what to do. Sometimes it won't start without being WOT, I think this is because of it flooding due to the miss. It will usually start just fine just runs like crap. I'm at a loss. I know it is intermittent spark. I just don't know why. Help please! :flamemad:
 
hows fuel pressure? also making sure that the fuel injector wires are not crossed. also that the spark plug wires are not crossed either.
 
hows fuel pressure? also making sure that the fuel injector wires are not crossed. also that the spark plug wires are not crossed either.

50 lbs constantly. It isn't a fueling problem, it is a spark issue. You can see it miss on the timing light I just have no idea why.
 
when its running does the tachometer drop and pop back up? if so your new ckps might be bad. or the wiring to it might be melted. does it have any check engine lights?
 
when its running does the tachometer drop and pop back up? if so your new ckps might be bad. or the wiring to it might be melted. does it have any check engine lights?

It does not, it stays right around 700 rpms. I've tried 3 different ckps in it, one was out of my running 96, occasionally it will throw a p0300. Which only tells me what I already knew! I wish it would narrow it down for me. If I put my timing light on the wire in between the coil and the distributor cap you can see it skip a beat every now and again. Is there anyway to test a pcm?
 
Also, if say one of the injectors are bad and it doesn't fuel it correctly, will it still spark? Or will it not spark because the pcm knows it didn't fuel it. This also all started happening after it overheated, well at least the guy I bought it from said that it ran fine before.
 
did you check the ignition coil? might just have a really weak spark.

I tested it for resistance, yes. It checked out. I backprobed the signal wire for the cam senor and it was also intermittent, but i swapped it with my other xjs cam sensor and there was no change.
 
Any chance it would be the PCM? I just find it odd that an electrical issue came from it being overheated. Catalytic converter?
 
can you check the input on the cam sensor. and see if that is intermittent. it could be the PCM. if you have one to test with you could.
 
Okay update, I pulled all the plugs and wires, and tested resistance in all of them. All of the plug wires where 4.5-5k, except 2 of them which where 6.5k and 7k. The plugs where all 8k ohms except 1 that was 10k ohms. Any ideas if that would cause this? The guy i purchased it from did the cap, rotor, plugs and wires. Not me. They are oreillys parts i believe. Autolite plugs.
 
can you check the input on the cam sensor. and see if that is intermittent. it could be the PCM. if you have one to test with you could.

also, i got ahold of the guy, he changed his story. This all started happening after he gave it a tune up.
 
id suggest redoing a tune up. cap rotor plugs. i have a feeling it will work fine after.

I did that yesterday thinking the same thing. No change, did plugs, wires, cap and rotor. All good parts. I'm going to redo my compression test and follow up.
 
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