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1991 XJ Speedo Issue - Tried Common Fixes, No Luck

LKN_xj

NAXJA Forum User
Location
Cornelius, NC
1991 XJ
231 T-case
335k miles
4.0 HO engine
Crown SYE

Currently racking my brain over a speedometer issue. Speedometer/odometer went out a while ago. It "fluttered" for a while and eventually stopped. makes me think it's electrical.

The speedo sensor on my T-case outputs to a 2-wire plug that runs above the transmission to another plug that feeds right into the main harness in the engine bay. It's literally its own standalone harness (plug on one end, plug on the other strung together with two wires: black/blue and white/red(pink?)

All other dash lights, gauges and indicator bulbs work perfectly. Only the speedo/odo isn't working.

Things I've tried:

1 - verified I have connection at the plug on the t-case. There is no oxidation on the plug or anything, looks great and plugs snugly into place. I don't have leads long enough that will let me check continuity of the wire from one end to the other of the harness but i'm fairly positive the sheathed wire isn't damaged.

2- took the gauge cluster out and tightened all screws for the speedometer unit. I've heard they can vibrate loose over time and cause the issue. No luck.

3- purchased a whole new gauge cluster from ebay and swapped it in with the exact same results. All gauges work except the speedo/odo.

4- cleaned and dielectric greased the other end of the two wire run in the engine bay. it was a little crusty but looks good now. No luck.

I'm at a loss. I can't find any fuses related specifically to the speedometer or anything like that. but regardless I checked all fuses that even remotely sounded like it could involve the speedo and all fuses are good.

Please offer opinions. Can't figure this one out. Thank you.
 
Did you pull the actual speedo gear out of the case and inspect? It is plastic and could have started slipping teeth then gone all together. If you get a new one make sure to order the one with the correct number of teeth. There are different tooth counts.
 
Did you pull the actual speedo gear out of the case and inspect? It is plastic and could have started slipping teeth then gone all together. If you get a new one make sure to order the one with the correct number of teeth. There are different tooth counts.



Yes I've tried two different gears and two different entire sensors.


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You don't just plug the sensor into the tcase. You have to insert it and rotate the whole thing until the gears mesh. It should actually have numbers on the clocking to guide you how far to rotate. If you look you will see that the speedo gear is not mounted right in the middle of the housing, it is off center.
 
How does the signal get to the dash? Through the ECU?

I had a similar failure but it was the sender and a ten minute fix .


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Thanks for chiming in. I'm not super savvy with electrical so you lost me a bit. The harness from the TC plugs into the main harness in the engine bay. I could try to trace that.

What is the sender and how did you fix that?


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There are two senders, the one I swapped was the one were the speedo gear goes. It's maybe a $30 comes with a small wiring harness. At least mine did, didn't need it so it's in the parts bin for the future

The other sender I've never touched so couldn't tell you about it, I think the transmission uses it .


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There are two senders, the one I swapped was the one were the speedo gear goes. It's maybe a $30 comes with a small wiring harness. At least mine did, didn't need it so it's in the parts bin for the future

The other sender I've never touched so couldn't tell you about it, I think the transmission uses it .


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Oh the "sender" you're talking about is the actual unit that slides into the TC housing that holds the speedo gear? Yeah I replaced that with no luck.


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Yeah. I though you had. Um, maybe test it?
Is there a way to power up the car and spin the sensor to see if it is working to the dash?




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Doing a search it's a common enough occurrence . Only solution so far is "connector under the hood off of the main wire harness pass side by the washer fluid reservoir. it runs from there under the jeep past the starter along the transmission to the speedo gear sensor. it got water in it."


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Yeah. I though you had. Um, maybe test it?
Is there a way to power up the car and spin the sensor to see if it is working to the dash?




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How would that be different than just driving the jeep? Not being sarcastic, but I'm pretty sure there's a hard stop in the casting that the speedo gear rides on and is forced to mesh with the shaft drive gear if installed. So I'm 99% positive the gear is turning.


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Doing a search it's a common enough occurrence . Only solution so far is "connector under the hood off of the main wire harness pass side by the washer fluid reservoir. it runs from there under the jeep past the starter along the transmission to the speedo gear sensor. it got water in it."


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Yeah, I'm positive my connections are clean and sealed. All plugs look great. I may have to start searching around for super long leads for my multimeter so I can reach from the t-case sender to the plug under the hood. Then find the other end after it leaves the main harness. Or make a really long jumper with some random wire to reach.


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No need for a jumper if you're trying to test continuity. Just unplug it and fish it into the engine bay.



Good point, could just drag it through. I'll do that and report back to make sure I have continuity from the TC to the engine bay.


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Doing a search it's a common enough occurrence . Only solution so far is "connector under the hood off of the main wire harness pass side by the washer fluid reservoir. it runs from there under the jeep past the starter along the transmission to the speedo gear sensor. it got water in it."


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Found the link you're referencing. Confirms it runs through the PCM.


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Here's another potential cause, though there seems to be lower hanging fruit to pick:

"Try replacing your spark plugs, spark plug wires, and coil (or coil rail). I had a similar issue to what you are seeing. To make a long story short, the coil was intermittently shorting out and sending high voltage spikes back to the PCM, which messed up my charging system and speedo. Replacing the coil fixed it for me."


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For some context, my folks bought this 1991 XJ in 1995 and it's been in the family ever since. It's been my daily driver since I turned 16 eleven years ago! Not only are you helping a forum member, but you're preserving a family heirloom in the process so thank you! Ha...


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