99 TJ 2.5 random misfire then fuel gauge drops

zlandquist

zlandquist

Member
Joined
Mar 7, 2019
Messages
37
Location
Wisconsin
Hey!
This has been an ongoing issue for over a year. It only happens during the summer/warm months.

When driving (after about 30 sustained minutes) the engine will misfire and throw a CEL. The CEL immediately clears itself. After the misfire, the fuel gauge will either drop to empty or go up to full. Sometimes it will only change the guage slightly.

While driving after that, the gauge will settle back.

The misfiring will happen as a single misfire or will happen rapidly. One time it was so bad I pulled over and as I was coming to a stop, the engine stalled itself (clutch in and in neutral)

I have replaced the ignition coil and done a full tune up (cap, rotor, plugs, wires).
 
When two unrelated things start behaving weird electrically & intermittently, you can bet there is a short and/or a bad ground.
 
CharlesHS said:
Disconnect the three PCM (ECU) 32 pin harness connectors and check the pins and clips for oxidation; then firmly snap the harness connectors into the PCM receptacles.
Click to expand...

Would you happen to have a picture to what I am looking for? I am still learning car stuff, and Google searching didn't get me comfortable enough. Thanks!
 
I would inspect the wiring harness back to the tank, chassis grounds, and the fuel pump module connector. Fuel pumps and fuel gauge circuits require a ground and this might be your common denominator.
 
  • Like
Reactions: zlandquist
For anyone that comes looking at this thread: the issue has been solved :)
It turns out the Crankshaft Position Sensor wire loom fell off the mount and got a bit toasty. One of the wires was split and holding on by about 3 strands and was grounding itself on the frame occasionally when bumping on the road.

I should note that the fuel gauge issue is still present. My mechanic friend suspects a grounding issue in the console.

PXL_20220826_191853725.jpg


PXL_20220826_191902894.jpg
 
Last edited:
Update:
The issue came back in full force. I had an electrical mechanic look at it. He was unable to really figure this out, he thinks it's a bad CPS again. This is really kicking me down.

Threw a no-bus error and was unable to start. Lost my blower motor too, just won't turn on. And the throttle issue is still present. Can't tell whether or not to throw in the towel.
 
If you found rotten wiring in one place and thought you found it all, I have bad news on a Friday for you. But strange behavior is almost always a bad ground or a short. The more intermittent, the more likely it's a ground. The stranger the behavior, the more likely it's a short.

But don't throw in the towel. The blower is a nice easy circuit to trace, I would start there. If you can resolve it, you may find the root cause of your other issues as well.
 
Top Bottom
Back