Speedometer not working

[hpd202]

Hi there. I have a 1998 Jeep Wrangler TJ and the speedometer is not working. The needle jumps around like crazy. I can be sitting still and it will go from 0 mpg to 130 mph and back down without ever touching the peddle. While I'm in motion it does the same thing. I have already changed the speedo gear and adjusted it to the correct ratio. I have changed the wiring harness to the speedo gear. I tried swapping out the instrument cluster and the issue still persists. I also hooked up a digital speed reader/guage to the PCM to see if the PCM speed reading matches the instrument cluster and it does. It jumps around like crazy too. I've done a lot a research and have received several suggestions that it could be a ground wire issue. I'm not the best with electrical stuff in cars and I need some help locating any/all ground wires that I should look to as the problem. Can anyone help me locate the ground wires that I should check? I did find one article showing locations for ground wires on a Jeep Cherokee WJ but I'd prefer to get something specific to a TJ unless everyone agrees the grounds will be in identical locations in a TJ. I have not tried to reference the article to my TJ yet. Unsure if its related but my after market stereo wont hold the time. It always resets on every start up and the bluetooth feature wont give me a good connection. The rest of the stereo works fine. I tried putting a new stereo with the same features and I get the same issues with it. My fuel gauge also is off by about a 1/4 tank but once again, after changing the instrument cluster that problem has not changed leading me to believe the fuel pump is going bad. But maybe its all one big related grounding issue?? Please help! Thanks! I've attached a short video of the issue. Please feel free to email if that is easier. Leenatelborg@hotmail.com

 

[Obi-Wan]

I think your jeep is telling you to get rid of that hideous grill, light bar, underglow and window decal. Nobody wants to be on the front page of The unfortunate TJ of the day thread.

And no, don't refer to the WJ for any wiring on your jeep, nothing will match up. Instead use the FSM (factory service manual) for your year TJ conveniently located at this forum.

Your radio needs a constant 12v power source to hold any settings including time. If it only has key on power, it will reset every time you turn the jeep off.

Your bluetooth is probably just s#!t, no wiring is going affect that.

Check that the plug on the speedo gear located on the driver side rear of your transfer case is fully seated / in good shape.

 

[hpd202]

If that's supposed to be a joke, I'm not laughing. I bought the Jeep that way and like it. The "fear this" decal was removed as soon as I bought it. You're actually the first person to ever make a negative comment about how it looks in the 2 years I've owned it.

As stated, I already checked, double checked, and triple checked the speedo gear. I have the FSM and still need to review it but if its loaded with electrical diagrams, those aren't my strong suit. I was hoping someone can just make this simple for me and tell me where the grounds are located. Like the guy did in the WJ article. He had photos and all.

My stereo does hold settings. All the preset radio stations are fine and audio settings. Just the time does not hold.

 

[tr21triton]

If that's supposed to be a joke, I'm not laughing. I bought the Jeep that way and like it. The "fear this" decal was removed as soon as I bought it. You're actually the first person to ever make a negative comment about how it looks in the 2 years I've owned it.

As stated, I already checked, double checked, and triple checked the speedo gear. I have the FSM and still need to review it but if its loaded with electrical diagrams, those aren't my strong suit. I was hoping someone can just make this simple for me and tell me where the grounds are located. Like the guy did in the WJ article. He had photos and all.

My stereo does hold settings. All the preset radio stations are fine and audio settings. Just the time does not hold.

snorkels and angry grills will get you banned from this forum !!!!

 

[hpd202]

Good grief. I thought this forum was for so called Jeep Wrangler experts to share their knowledge and help anyone out with a Jeep no matter if you are new to the Jeep world or been in it for years. I didnt realize it was a cliquey high school group who get off on mocking others who ask for help. Thanks for nothing. Ill search for the experts elsewhere.

 

[pagrey]

The speedometer uses the same voltage reference as a few other sensors that control the engine. If you are getting strange behavior in just the speedometer I'd really carefully trace the wire from the transfer case at the sensor forward. If you are having radio issues it's possible that when the radio was put in a ground behind the deck was cut or messed up. You might pull the deck and take a good look behind the radio. The service manual @Obi-Wan linked to does have the ground locations. I'd check the easy ones first, battery cables and the ground that goes to the engine block and firewall, all that stuff is near the battery. Beyond that I think there are grounds behind the instrument cluster but since the PCM has bad data that seems like it's probably not the issue.

 

[hpd202]

The speedometer uses the same voltage reference as a few other sensors that control the engine. If you are getting strange behavior in just the speedometer I'd really carefully trace the wire from the transfer case at the sensor forward. If you are having radio issues it's possible that when the radio was put in a ground behind the deck was cut or messed up. You might pull the deck and take a good look behind the radio. The service manual @Obi-Wan linked to does have the ground locations. I'd check the easy ones first, battery cables and the ground that goes to the engine block and firewall, all that stuff is near the battery. Beyond that I think there are grounds behind the instrument cluster but since the PCM has bad data that seems like it's probably not the issue.

Thank you!

 

[Kelly F.]

I'll piggy back off this. I recently disconnected the battery in my TJ and the fuel gauge cluster worked for the first time since I've owner my Jeep. BUT as soon as I shut the jeep off, fuel gauge no longer worked like before. I've cleaned all connectors before, issue remained.
I've also had my entire cluster go whack, cleaning and reconnecting everything corrected that problem.
Weird the fuel gauge worked temporarily after disconnecting the battery. Suggestions?