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Full OBD1 HO 4.0L Swap - What Wiring Can I Keep/Toss Out?


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Hey all! First time

 

A few months back I bought an '87 MJ as I've always liked them. However, I bought someone else's project and it's turned into a bit of a headache.

 

To complete the project I purchased a '91 XJ for an engine swap. I pulled the wiring harness from the XJ and am struggling to know what I need to keep to run the motor and what I don't. I've done a lot of searches around the web and have yet to find a write up of the same swap I am attempting. Can anyone point me to some threads here or elsewhere? Much thanks in advance. 

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how much of the XJ's wiring did you grab?  dash harness too?  rear lights wiring?  is the XJ still around to pull more stuff?

 

are you swapping just the engine?  or the trans too?  essentially everything changed in 91 for the HO and the chrysler electronics.  on the surface it all looks very similar, but Renix and Chrysler used different sensors and ran their wires different.  so essentially everything needs to swap over to get the HO computer and the gauge cluster to work.  

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Chrysler used to sell a kit for converting the carburetted 4.2L Wranglers to electronic fuel injection. The kit was basically the complete engine room harness from a '94 Wrangler 4.0L. All the engine sensors are different, the ECU is different and mounts in a different location. I have not done the conversion, but basically you are scrapping everything that's associated with your engine and computer, and you're keeping the wiring that runs things like horn, headlights, brake & tail lights, and hazard flashers. The CPS for the HO operates on a different principle than the Renix, so in addition to replacing the wiring you will have to replace the CPS.

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29 minutes ago, Eagle said:

Chrysler used to sell a kit for converting the carburetted 4.2L Wranglers to electronic fuel injection.

 

Jegs, Quadretec, Hesco, and others still sell the Mopar MPI conversion kit. A mere $2,960.99 to your door.

 

https://www.jegs.com/p/Mopar-Performance/Mopar-Performance-Jeep-MPI-Conversion-Kit-and-Service-Parts/1908371/10002/-1

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27 minutes ago, Eagle said:

The CPS for the HO operates on a different principle than the Renix, so in addition to replacing the wiring you will have to replace the CPS.

 

 

and the tone ring (or whatever they called it back then) needs to match the new CPS.

 

 

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3 hours ago, Pete M said:

how much of the XJ's wiring did you grab?  dash harness too?  rear lights wiring?  is the XJ still around to pull more stuff?

 

are you swapping just the engine?  or the trans too?  essentially everything changed in 91 for the HO and the chrysler electronics.  on the surface it all looks very similar, but Renix and Chrysler used different sensors and ran their wires different.  so essentially everything needs to swap over to get the HO computer and the gauge cluster to work.  

 

I still have the XJ and can pull more wiring. The wiring I pulled yesterday included everything in the engine bay all the way to the brake module that sits under the rear seats. I have not grabbed the fuse block and everything connected to it. Honestly, I was hoping to avoid that...

 

As far as drivetrain, I am only swapping the engine as I have an AX-15/NP231 I already installed.

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1 hour ago, Pete M said:

you'll need an HO flywheel's tone ring to make the HO CPS work.  there should be some HO swap info threads in the link in my sig.

 

Those links are helpful, thank you.

 

2 hours ago, Pete M said:

 

 

and the tone ring (or whatever they called it back then) needs to match the new CPS.

 

 

 

Damn. I am pretty sure my flywheel is a non-HO.

 

2 hours ago, HOrnbrod said:

 

Jegs, Quadretec, Hesco, and others still sell the Mopar MPI conversion kit. A mere $2,960.99 to your door.

 

https://www.jegs.com/p/Mopar-Performance/Mopar-Performance-Jeep-MPI-Conversion-Kit-and-Service-Parts/1908371/10002/-1

 

I think I'll pass...

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5 hours ago, Pete M said:

 

and the tone ring (or whatever they called it back then) needs to match the new CPS.

 

 

:doh: Absolutely correct, and I skipped over that because I interpreted the opening post as saying that he was going to use the engine from the HO, so it would have the correct flywheel or flexplate.

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Thanks for everyone's help. After looking through some things I'm currently on the hunt for an HO TPS and flywheel. I'll also be swapping over the fuse block and the rest of the body harness tomorrow. 

 

Can anyone tell me why my AX-15 trans shifter doesn't line up with factory holes for the shifter or why my crossmember doesn't line up? I'll send pictures tomorrow if that's helpful.

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What transmission was in the vehicle originally?  The AX-15 takes a few specific parts to swap into something that has/had a different transmission in it previously.  For the shifter, I'm assuming you're talking about where it comes up through the trans tunnel.  There's a black metal cover plate on the tunnel inside the cab.....the AX15's cover plate is different from the AX5 or AW4 (probably the BA10/5 too, but I've never messed with one of those).  For the crossmember, there are additional holes in the framerails to move the crossmemeber forward or backwards depending on the trans.  The AX15 uses the last set of holes, furthest back toward the rear.  As well, the AX15 uses a specific crossmember that has a "dip" in the center of it to align the drivetrain height in the tunnel.  If you're using a different one, the trans will sit too high in the tunnel.  Last, but not least, if you're 4WD, you'll need the transfer case shifter bits from the AX15 as well.  At least the bracket that bolts to the trans tunnel (the little heim ball that the trunion rod fits into is all the way to the rear on the AX15 bracket, the other tranny brackets have it centered).  You'll also need the shift rod from the AX15 shifter assembly that attaches the bottom of the shifter to the linkage on the transfer case.....it's much shorter compared to the AX5 and way shorter than the AW4 rod.  You could eliminate all of the BS factory craptastick shifter assembly with aftermarket stuff as well......costs $$$ but is much simpler and more reliable.

 

Jeff

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