Weird electrical issues on Jeep TJ

The last few months I have been trying to track down some weird electrical issues. I need to keep going though the wiring and the grounds, but I’m far from an expert when it comes to electrical issues. The issues an intermittent and seem to be more common when it’s raining or fogging (so moisture).

Here are the issues in no particular order:

Issue #1: Transmission won’t shift from 2nd to 3rd.
When going from complete stop up to speed, sometimes it will have issues shifting from 2nd to 3rd leading to the RPMs getting super high and I have to stop and pull over and turn the car off and then turn it back on and that will allow me to get up to third or fourth one more time and then I might have to do it again.

Here is a video of this issue

Issue #2: Crank but no start.
Usually it does this just once and I’ll try again and it will start, but the most recent time it didn’t start and I haven’t been able to get it started back yet. I don’t have a voltage meter with me to check the battery but the gauge on the cluster says it’s right at the first dot so that should be good to start off I think.

Here is a video of this issue

Issue #3: Rough Idle that seems like a slight misfire but no misfire code.
When idling it sounds like a slight miss especially from inside the car. It’s so slight that you can’t really hear it on camera but it’s definitely there.

My troubleshooting so far:
This all started after an off road trip where maybe some water got into something. Since then I changed the spark plugs which helped for a time. Changed fuel rail. Tried changing the fuel injectors which seemed to make things worse so I swapped back to the original ones. And also changed to a Wrangler Fix computer.

Thinking about changing the wiring harness but need help on what to try next. Thank you for all the help!

Okay so I replaced the battery and that fixed the issue number 2 (Jeep will start), but the other issues remain.

Any assistance on how to find what part of the wiring could be at fault or any other tips would be appreciated.

For the transmission I called a transmission shop to see if they could figure it out, and they said since it’s intermittent, it would have to be electrical, and they only work on the transmission itself. So I know that part has to be some sort of electrical issue and I’m assuming that engine issue is probably related.

LONGJP2 said:

Check the harness where it wraps around the back of the engine (passenger side).
It's known to chafe there.

Click to expand...

Thank you for this tip. I opened up the plastic covering on that and the wires all look fine. It doesn’t look chafe there but maybe there’s something going on that I need to do electrical testing for but don’t know exactly what to do.

Any thought on the transmission part of this issue?