2.5 Renix to 4.0 HO swap fuel gauge reading correct

[WiscoXJ]

I have spent the last few hours reading up on this and can't find a sure thing answer on it so here is what I have so far:

 

I will be swapping a XJ HO full dash and harness into my renix 2.5 MJ. I want my full gauge to read right.  SO, the part numbers for both the 2.5 and 4.0 renix fuel tanks are the same meaning the fuel pumps are interchangeable. HO 4.0 and renix 4.0 mj tanks part numbers match meaning I can put a HO pump and sender in my renix tank. Great. I have the dummy light cluster in my MJ so the XJ cluster will be coming over too which means I will have the correct gauge to read the sender theoretically.  I will be modifying the MJ rear harness to correctly mate up with the rest of the XJ harness.

 

So the question of the hour is: Are there any big wiring differences that won't allow this to work? I couldn't find a total confirmation on this but someone has to have done it.

 

This is the MJ to XJ harness splice I plan to do:

http://comancheclub.com/topic/18588-xj-dash-harness-to-rear-mj-harness-wiring-guides/

 

Someone please confirm this for me!

[mnkyboy]

I have a 91 fuel pump and sender in my original renix tank, everything fit the same. I am using a 91 wiring harness spliced into the renix rear harness with a 4.0l cluster and everything works.

 

Mines a 2.5l but it shouldn't matter.

[WiscoXJ]

That's exactly what I wanted to know. Thank you for confirming that!

 

Now to take it further.. Has anyone used a renix cluster or sender with the opposing sender or cluster so that it reads backwards and 1/4 tank off and modified the wiring so that it read in the right direction just not at the correct level? When I do this swap I will ohm out both gauges and see what they come to. hopefully we can make a right up for repinning some wires and soldering in a different resistor so one doesn't have to do a sender or cluster swap if they don't want to!

[mnkyboy]

Your better off swapping clusters,the renix cluster isnt plug and play with the HO stuff. Renix has a cable driven speedometer and the HO is electronic.

 

I imagine with a pass through speed sensor you might be able make the renix cluster work but it would be alot easier to swap in the HO one.

 

My original plan was to hybrid the renix and HO harness together and run dual senders with the renix cluster, it ended up being easier and alot cleaner to use the newer stuff.

 

Never got into fuel sender stuff as far as crossing them, I was going to use the sender for what ever cluster I went with.

[HOrnbrod]

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

[WiscoXJ]

Mnkyboy, u said u put an HO sender in your original Mj tank? Is it a Comanche sender or is it the xj version?

[mnkyboy]

I got it from a 91 MJ.

[WiscoXJ]

That makes more sense..

[Eagle]

That's exactly what I wanted to know. Thank you for confirming that!

 

Now to take it further.. Has anyone used a renix cluster or sender with the opposing sender or cluster so that it reads backwards and 1/4 tank off and modified the wiring so that it read in the right direction just not at the correct level? When I do this swap I will ohm out both gauges and see what they come to. hopefully we can make a right up for repinning some wires and soldering in a different resistor so one doesn't have to do a sender or cluster swap if they don't want to!

You shouldn't need any resistors. The ohm range for the Renix is 0 to 88. The range for the HO is (IIRC) something like 104 to 4. The substantive difference is the reversed polarity. You can fix that by tracing the two leads from the fuel gauge back to the plug at the back of the cluster. Remove the corresponding two wires from the plug and reverse their positions.

[WiscoXJ]

I'm going to pull both senders and bench test them both and get some real numbers. I've read so many threads where people "wish they would have done that" so I'll be that guy and take pictures and post. I'm going to take measurements if how and where an Mj sender sit and see what it would take to make one work if that would be a persons only option. Then we'll if we can get this thread stickied so this same topic doesnt keep coming up

[HOrnbrod]

 

That's exactly what I wanted to know. Thank you for confirming that!

 

Now to take it further.. Has anyone used a renix cluster or sender with the opposing sender or cluster so that it reads backwards and 1/4 tank off and modified the wiring so that it read in the right direction just not at the correct level? When I do this swap I will ohm out both gauges and see what they come to. hopefully we can make a right up for repinning some wires and soldering in a different resistor so one doesn't have to do a sender or cluster swap if they don't want to!

You shouldn't need any resistors. The ohm range for the Renix is 0 to 88. The range for the HO is (IIRC) something like 104 to 4. The substantive difference is the reversed polarity. You can fix that by tracing the two leads from the fuel gauge back to the plug at the back of the cluster. Remove the corresponding two wires from the plug and reverse their positions.

 

 

That will not reverse polarity to the gauge, it only shifts the sender pot slider sensing point. To reverse polarity you have to do it at the sender potentiometer; remove the output lead from the + potentiometer leg to the opposite - leg at the sender. The ohm difference between the Renix and HO pots is negligible, but will cause a ~20% difference in the fuel gauge indication. 

 

[HOrnbrod]

I'm going to pull both senders and bench test them both and get some real numbers. I've read so many threads where people "wish they would have done that" so I'll be that guy and take pictures and post. I'm going to take measurements if how and where an Mj sender sit and see what it would take to make one work if that would be a persons only option. Then we'll if we can get this thread stickied so this same topic doesnt keep coming up

 

Do it.  :cheers:

[WiscoXJ]

Wish me luck!

 

My buddy just called me and is trying to convince me to put a 20 gallon cell in it.. Tempting.. Either way I will figure it out!

[Dillithium]

I was going to be that person when I fixed my sending unit, I wanted to take pictures and everything. The fuel smell was so overwhelming, I couldn't wait to get it back into the tank. I just rushed through it, I hope you do better.

[Eagle]

 

 

That's exactly what I wanted to know. Thank you for confirming that!

 

Now to take it further.. Has anyone used a renix cluster or sender with the opposing sender or cluster so that it reads backwards and 1/4 tank off and modified the wiring so that it read in the right direction just not at the correct level? When I do this swap I will ohm out both gauges and see what they come to. hopefully we can make a right up for repinning some wires and soldering in a different resistor so one doesn't have to do a sender or cluster swap if they don't want to!

You're right.

 

My only excuse is that it was late and I was tired.

 

You shouldn't need any resistors. The ohm range for the Renix is 0 to 88. The range for the HO is (IIRC) something like 104 to 4. The substantive difference is the reversed polarity. You can fix that by tracing the two leads from the fuel gauge back to the plug at the back of the cluster. Remove the corresponding two wires from the plug and reverse their positions.

 

 

That will not reverse polarity to the gauge, it only shifts the sender pot slider sensing point. To reverse polarity you have to do it at the sender potentiometer; remove the output lead from the + potentiometer leg to the opposite - leg at the sender. The ohm difference between the Renix and HO pots is negligible, but will cause a ~20% difference in the fuel gauge indication.