Random cylinder misfires on 2000 TJ 4.0

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dbshuffle

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Hello,

I got a 2000 TJ with the 32RH transmission, on 33's. I've been getting random cylinder misfires, had multiple shops take a crack at it, even replaced the coil pack. I've gone weeks without it popping but usually up in the mountains I'll get flashing CEL and eventually the solid, and have gotten all of the 300 level codes.

It's still geared at 3.73 but when I'm on the mountain highways I lose speed going uphill. Is this due to the gearing or is it possible the cylinder misfires are part of the issue?
 
If it's misfiring you will lose some power. If it goes into limp mode you won't be able to go above about 2000 rpm, meaning you won't go very fast at all. But even without limp mode you still lose some power.

3.73 is actually a decent ratio for the 32RH and 33s. With the torque converter locked you should be doing about 2700 RPM at 70 mph, more with the torque converter unlocked. You may even be able to use 2nd gear at 70mph, depending on how much the torque converter slips. That would certainly get you the torque at the wheels you need to climb hills.

As for the misfires, I don't have as much advice. I recently had a similar misfire. It got bad enough it sent me into limp mode multiple times. It turned out one of my catalytic converters self-gutted and clogged the 3rd cat. I ended up replacing it with the Magnaflow unit which solved my issue.
 
What spark plugs are you running? What are they gapped to? Have you tested the coil packs to make sure each one is firing?

If multiple shops haven't been able to fix it, I'd say you're dealing with some pretty incompetent shops :rolleyes:
 
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Chris said:
What spark plugs are you running? What are they gapped to? Have you tested the coil packs to make sure each one is firing?

If multiple shops haven't been able to fix it, I'd say you're dealing with some pretty incompetent shops :rolleyes:
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+1 to check the simple stuff first. I was fighting a misfire/CPS/CKS and after checking the torque and gaps on my spark plugs things resolved.

Though sometimes diagnosing a problem may take a few tries as you narrow in on the issue, a shop shouldn’t put you on the hook for their inability to fix it and just throwing parts at the problem. Some of that responsibility may be on you to learn the right questions to ask before approving any work (and jumping shops).
 
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plugs have been changed 2x along with 02 sensor and coil pack. i will find out what kind of plugs they put in this time tomorrow. thank you
 
Take the oil cap off and take a pic with your camera lens directly over the opening. Hopefully you will see “TUPY” down in there. If not, you may be about to blow a head gasket.
 
can you elaborate? i've seen some posts where this is the culprit if you are getting a recurring misfire on a specific cylinder, and I'm getting all of them at times and the random code... thank you
 
auttiman said:
Take the oil cap off and take a pic with your camera lens directly over the opening. Hopefully you will see “TUPY” down in there. If not, you may be about to blow a head gasket.
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These are probably different issues. It's not the head gasket that blows on 00 and 01 4.0s; it's the head that cracks. Only 2002 and later had TUPY 0331 heads, unless it's been replaced. Unless he is losing coolant, this does not sound like his issue.
 
the plugs they put in are Champions. They said next they want to put it up on the Dyno and see if they can replicate the issue and see what they find.
 
I just got through chasing a misfire on every cylinder and had to take it to a shop as I was out of ideas. They replaced the plugs with double platinum 985's, new plug wires and adjusted the timing (it was off). They also fixed the clock spring for the horn (which believe it or not I have read can throw a misfire code!?). This took care of my problem but YMMV. Mine would shake and shudder and barely make it up an incline on the road as well as idle weird and misfire sitting still.
 
dbshuffle said:
the plugs they put in are Champions.
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Exactly what model Champion plugs? If they're the 3034 and you have the coil pack (no distributor cap) system that's your problem. If they're the correct plug my next suspicion for a random misfire would be the CPS (crankshaft position sensor) bolted onto the flywheel housing.
 
Jerry Bransford said:
Exactly what model Champion plugs? If they're the 3034 and you have the coil pack (no distributor cap) system that's your problem. If they're the correct plug my next suspicion for a random misfire would be the CPS (crankshaft position sensor) bolted onto the flywheel housing.
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Jerry are the coil packs the problem? I’m asking because a friend said he saw where some are replacing the coil rail with a distributor and spark plug wires.
Please advise and TIA
 
mechanic said the injector timing through the camshaft was 20 degrees off. took it on a 150 mile mountain drive, and it did do a flashing CEL a couple times but did not put out a code...
 
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