91-92 Mj Fuel Gauge Senders

[Keyav8r]

If I understand the subject correctly, the fuel gauge senders in 91 & 92 MJs are specific to only those years and only MJs. The gauge in my 91 doesn't work, although it has moved a couple of times since I got the truck. I believe I read that the signal polarity is reversed from earlier years.

Is there any way to test the sender while it's still in the tank, on the truck?

Is there any way to test the gauge?

And, are there any gauge clusters that will swap in?

Does anyone repair the senders?

[GirsMJ86]

They aren't actually specific to those years only, and you can even use an older one if you want (or vice versa if you have an older rig and use a 91+ unit). The only difference is the polarity, all you have to do is swap the wires and it should read correctly. My old '91 had an older sender unit in it and the wires were not swapped, all that happened is it read backwards on the gauge. I got used to it and didn't care, sure freaked out passengers though.

[HOrnbrod]

Nothing will "swap in" and work correctly and accurately that's not from a 91-92 MJ. Not an XJ or older Renix MJ unit. "Swapping wires" because the polarity is different has to be done internally on the sender, but it still will not read accurately since the potentiometers are of different values. This thread will explain most of it:

 

  http://comancheclub.com/topic/15047-ho-fuel-sending-unit/

 

There is a test in the FSM to test the gauge w/o pulling the sender; I'll look it up later and post. A faulty gauge is seldom the problem though. There are also outfits that will repair fuel sending units, but you'll have to pull it to see what the problem is. Could be something as simple as a broken wire on the potentiometer.

[GirsMJ86]

Good thing you chimed in Don, I completely forgot the wire swapping was done internally. 

[Keyav8r]

I thought I had posted this but can't find it on the forum. If I understand it correctly, the fuel gauge senders on 91& 92. MJs are specific to those years and to MJs. The gauge in my 91 doesn't register the fuel level but I have seen it move a couple of times. So, I'm trying to determine how to diagnose the problem.

 

Tach, oil pressure and temp gauges work, but the volt meter and fuel gauge don't..

 

I assume the sender will have to be removed from the tank to test it. Hook the leads up to an ohmmeter and move the float arm through its travel and watch for a change in reading? What should the ohm range be?

 

Is there any way to test the gauge? And is the only replacement another gauge cluster?

 

Am I right that there are no sender options for the 91 & 92 MJs?

[Eagle]

The early ones were 0 to 88 ohms. Going from memory, the later ones were something like 4 or 8 ohms to about 108.

[Geonovast]

Given that you are having problems with another gauge, I would pull the cluster and inspect the foil on the back and the connections to the gauges.

[Keyav8r]

Eagle - Thanks for the ohm ranges. One step closer to the solution. But, as we know, with MJs one step can be the beginning of a long journey

 

Geonovast - Excellent suggestion. Has to be easier than pulling the pump and sender. If needed, a replacement cluster would have to come from another 91 or 92 MJ, right?

[Geonovast]

Cluster can come from a 91 or 92 MJ, or 91-96 XJ.

[HOrnbrod]

Your original post on this topic is here:  http://comancheclub.com/topic/39328-91-92-mj-fuel-gauge-senders/?do=findComment&comment=395903

 

91-92 MJ fuel gauge sender pots are 105 ohms (Empty) to 5 ohms (Full)

 

Fuel gauge inop checks:

 

1.  Turn IGN to RUN

2.  Disconnect fuel gauge sender connector. Needle should go to EMPTY.

3.  If it does not, you either have an open between the sender connector to the cluster, or the fuel gauge itself is bad (unlikely).

 

Do these checks first. If step 2 fails, you then have to check for continuity between cluster connector B1 and the fuel sender connector.

 

You really need an 1991 FSM to work on stuff like this. 1991 was the first year for OBD1, and there were quite a few wiring schemes unique to the 91. Same for the 96 XJs, the first year of OBD11.

[Keyav8r]

Yep, I definitely lost the thread. Looked all through the forums and couldn't find it. Ordering a 91FSM is on my list of things to do and I just bumped it closer to the top. Saw some on ebay earlier, just didn't pull the trigger. Thanks for leading me back to the first post

[87MJTIM]

For FSM's i found this to have a complete selection of books:

 

www.faxonautoliterature.com

[Eagle]

The difference in the ohm range is insignificant, IMHO. Factory fuel gauges aren't all that accurate, anyway. The real problem is the change in polarity. The '91 and '92 are 105 ohms for empty, where the early years were zero ohms empty and 88 ohms full. Obviously, a mismatch between the sender and the gauge will cause the gauge to read backward (as well as to be slightly [more]inaccurate).

 

One solution would be to go to the hydra plug where all the wires plug onto the gauge cluster. Identity the two wires that are for the fuel gauge. If you can pull those wires out, just do so and reverse them. If you can't remove the push-in connectors, clip the wires and splice to the opposite stubs.

[Pioneerproblems]

Sorry to get off topic here but does anyone know offhand which color wire goes to the sending unit and which powers the fuel pump? 
 

I’m running a fuel cell and decided knowing how much gas I have would be cool

[JMO413]

Here's what the electrical manual shows.