1991 XJ Speedo Issue - Tried Common Fixes, No Luck

[Green Mesa XJ]

Should be right by the airbox. A few 10mm hold it if I remember right.
Just match the numbers up, should be plenty available


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[LKN_xj]

Should be right by the airbox. A few 10mm hold it if I remember right.


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10-4. Does that require a reprogramming sequence to configure the jeep to it or plug and play?


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[Green Mesa XJ]

Plug and play. I have a spare because of this very issue. First time it happened I thought it was the pcm, speedometer disappeared at 75 mph for a bit then came right back. didn't happen again for a few years and that time it was the sender .


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[LKN_xj]

Okay got it. As long as the numbers match? I also found this as cheap insurance

https://m.summitracing.com/parts/sm...tor-products&gclid=CLOz-8b2j84CFcZahgodMsUJLQ


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[Green Mesa XJ]

I thought you already changed it already? Another backup?

I think it's a 91 only, the last two letters in the number may fluctuate according to revision .


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[Green Mesa XJ]

Well it looks like 1991-92 interchange .
Look at the parts searches there may be a few numbers that will work but I'd try to keep it the same #.

Only hiccup is if you have California emissions . I know federal is plug and play. Also it's probably all numbers I was confusing later jeep years that use letters at the end of part numbers.


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[LKN_xj]

I thought you already changed it already? Another backup?

I think it's a 91 only, the last two letters in the number may fluctuate according to revision .


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I did already change it but I changed it out with another used one. At least this would eliminate the variable of the used replacement also being faulty.


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[LKN_xj]

Well it looks like 1991-92 interchange .
Look at the parts searches there may be a few numbers that will work but I'd try to keep it the same #.

Only hiccup is if you have California emissions . I know federal is plug and play. Also it's probably all numbers I was confusing later jeep years that use letters at the end of part numbers.


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We're talking about the PCM, not the sender yea?


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[Green Mesa XJ]

Yes. It will be something like 56027488.
I used to have a list with all the jeep ecu/pcv numbers.

Far as I know the sender is the same across the years.


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[LKN_xj]

Here's one on eBay that seems to validate 91-92 match your example number you just listed:

https://www.ebay.com/itm/152146625911

But my number is 56027528. For some reason the ones that match my number are $50 more expensive.

https://www.ebay.com/itm/112051498576

I'll probably see if the sender works after validating I have continuity, then see if a junk yard has a PCM that matches my number.


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[Green Mesa XJ]

Check with local yards or car-parts.con for yards around the area

Someone here may know what interchanges .


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[old_man]

Did you ever rotate the sensor in the tcase to make sure the gear was meshing? This is a common problem.

 

[Digger87xj]

Lets clear up a few things. This is not rocket science.

1..This sensor is a simple pulse generator. The black/blue wire is ground, and a voltage is generated on the white/orange wire. This can be checked for output with a voltmeter and a drill driving the gear. reference http://www.speedwaymotors.com/Tech/Testing-2-and-3-wire-speed-sensors.html
do the 2 wire sensor test

2. The ECM does NOT feed the I/P VSS info. The white/orange wire has a splice in the harness.. one goes to the ECM, the other goes to I/P (through a connector, 12 pin, black, behind the left kick panel), and yet another to the daytime headlamp module, if it's a Canadian model.

Don't replace the ECM for speedo inop!

My bets are that you have corrosion or disconnect between the splice and the IP, as you are not getting a CEL for VSS from the ECM.

 

[LKN_xj]

Lets clear up a few things. This is not rocket science.

1..This sensor is a simple pulse generator. The black/blue wire is ground, and a voltage is generated on the white/orange wire. This can be checked for output with a voltmeter and a drill driving the gear. reference http://www.speedwaymotors.com/Tech/Testing-2-and-3-wire-speed-sensors.html
do the 2 wire sensor test

2. The ECM does NOT feed the I/P VSS info. The white/orange wire has a splice in the harness.. one goes to the ECM, the other goes to I/P (through a connector, 12 pin, black, behind the left kick panel), and yet another to the daytime headlamp module, if it's a Canadian model.

Don't replace the ECM for speedo inop!

My bets are that you have corrosion or disconnect between the splice and the IP, as you are not getting a CEL for VSS from the ECM.

That was a wealth of knowledge - thanks for chiming in. I'll do the drill test too, that seems simple enough. Do you happen to know if the splice going to the I/P is in the engine bay or in the dash so I can direct my search for corrosion at that junction?

That was a great link - thank you.


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[LKN_xj]

Did you ever rotate the sensor in the tcase to make sure the gear was meshing? This is a common problem.

I haven't quite figured out in my head how it's possible for it to be misaligned. If the speedo gear shaft runs down the centerline of the adapter that mounts to the T-case, rotating it would only rotate the gear along its own axis. If it were off center I can see how rotating would cause it to mesh. I've noticed there are three hash marks on the top of the adapter, two of which grab the prongs on the plate that bolts to the tail housing. Is there an orientation of those marks that guarantee meshing of the gear teeth?

It appears there's supposed to be an alignment nipple per tooth size on the tail housing. I have a SYE so I'll have to look after work and see if I also have this alignment bump.


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[Digger87xj]

I was looking it up as you answered...

Splice G7 is located under the hood in the main harness on the firewall, right side of the engine bay to the left (right as you are looking at it) of where the transmission harnesses enter the main harness.

I'll see if I can link a photo...

 

[Digger87xj]

I haven't quite figured out in my head how it's possible for it to be misaligned. If the speedo gear shaft runs down the centerline of the adapter that mounts to the T-case, rotating it would only rotate the gear along its own axis. If it were off center I can see how rotating would cause it to mesh. I've noticed there are three hash marks on the top of the adapter, two of which grab the prongs on the plate that bolts to the tail housing. Is there an orientation of those marks that guarantee meshing of the gear teeth?

It appears there's supposed to be an alignment nipple per tooth size on the tail housing. I have a SYE so I'll have to look after work and see if I also have this alignment bump.


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The speedo gear shaft is offset from the center of the housing. This allows the housing to be rotated for different diameter gears to mesh the drive gear.

 

[LKN_xj]

The speedo gear shaft is offset from the center of the housing. This allows the housing to be rotated for different diameter gears to mesh the drive gear.

That answers that!


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[Digger87xj]

 

[Digger87xj]

The splice you want is G7.. near dead center in the pic