Almost Done!!!

[ORMJ]

Just finished 4.0 renix swap replacing my 2.5L. Both jeeps are 89's can I splice into the original wiring to get the 4.0 operating or will i have to do a wiring swap out of donor rig? They are both the same year, if that helps. I HATE electrical.

[Pete M]

A wiring swap is necessary. They don't share computers.

[mjeff87]

you're gonna need the 4.0 engine bay harness, including the ECU. Looks like this ;)

 

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[JeepcoMJ]

aaand the interior wiring harness is necessary BECAUSE the pin connector (bulkhead connector, the piece that the engine harness plugs into) is completely different pinouts. it will not start with the 2.5 harness in place, and it sure as hell won't run

[mjeff87]

I don't want to put out bad information, and I don't want to come across in the wrong way JeepcoMJ, but have you actually done this swap? Reason I ask is that I've been doing serious amounts of research on it in prep for mine, and it doesn't appear you need the interior harness to make it work. I've talked with three different people who have done this swap successfully, one used the interior harness but the other two simply plugged the engine harness into the bulkhead of the 2.5 harness and everything worked. One even used an XJ harness, and both of the two used different model year engine harnesses than what their vehicle was.

 

I've also researched thru FSM's and dealership parts catalogs, and the same interior harness p/n was used for each model year from 87-89, regardless of drivetrain (engine or transmisson, 2 or 4WD). The only difference in interior harnesses is diesel versus gas engine. On the gas models, seperate engine harnesses are listed, but each plug into the same bulkhead connector, which is hard-wired to the same fuseblock, and associated interior harness that has the same part number.

 

 

Leaving the 2.8 and diesel out of the discussion, the only differences in the engine harness between a 2.5 and a 4.0 Renix are the injector circuits, cam sensor, knock sensor, and location of the EGR solenoid from what I've compared....and none of those feed thru the bulkhead connector. They only go to the ECU (which is different, of course).

 

Jeff

[JeepcoMJ]

I've heard of 4 people doing the swap, who have had to redo the entire interior AFTER wasting time trying to figure out why it don't work.

 

...have I myself done it? no. but, I did yank a 2.5 harness and a 4.0 connector and looked at the wiring, and it appears different. also, alldata shows that it's different diagrams...i can't direct link to those pics though.

[Eagle]

I don't want to put out bad information, and I don't want to come across in the wrong way JeepcoMJ, but have you actually done this swap? Reason I ask is that I've been doing serious amounts of research on it in prep for mine, and it doesn't appear you need the interior harness to make it work. I've talked with three different people who have done this swap successfully, one used the interior harness but the other two simply plugged the engine harness into the bulkhead of the 2.5 harness and everything worked. One even used an XJ harness, and both of the two used different model year engine harnesses than what their vehicle was.

 

I've also researched thru FSM's and dealership parts catalogs, and the same interior harness p/n was used for each model year from 87-89, regardless of drivetrain (engine or transmisson, 2 or 4WD). The only difference in interior harnesses is diesel versus gas engine. On the gas models, seperate engine harnesses are listed, but each plug into the same bulkhead connector, which is hard-wired to the same fuseblock, and associated interior harness that has the same part number.

 

 

Leaving the 2.8 and diesel out of the discussion, the only differences in the engine harness between a 2.5 and a 4.0 Renix are the injector circuits, cam sensor, knock sensor, and location of the EGR solenoid from what I've compared....and none of those feed thru the bulkhead connector. They only go to the ECU (which is different, of course).

 

Jeff

I only know one guy who did this swap, a friend from the early NAXJA days. I should mention that at the time he was a student in electronics at a technical university, and basically an electronics genius. He said he had to swap the ENTIRE harness, and I have no reason to doubt him.

 

You can't just plug into the bulkhead connector for the simple reason that the ECU for the Renix years is mounted inside, under the dash, and the wires to it come from the bulkhead connector. And if you get a FACTORY wiring diagram, you'll see that the pinouts for the 4.0L ECU are dramatically different from the 2.5L ECU.

 

Go ahead and try it if you think it'll work. I'm curious to see how you'll make out, but I've been researching the same thing and I am fully anticipating that I'll have to swap the entire harness from the donor vehicle.

[Oizarod115]

an entire swap won't be nearly as bad as a hackjob... and you'll want to shoot yourself 6months from now if you hack it to make it work.

 

just get all the wiring from the donor if its easily available... it'll pay off in the long run

[ORMJ]

Thanks for the help, I'm still scratching my head. It sounds like I will do the entire swap. I have 3 89 MJ's, I just want one good one :brows: my girlfriend of 8 years says I have a disease.

[M2 CARBINE]

I started off the same way replaced only the engine bay harness after 1 month of trying to troubleshoot what the prob was some one pointed out i needed to replace every wire from the donor after that was done i turn the key and fired right up

 

 

went from 2.5 5sp man to 4.0 auto in about 8 months cause i didn't know i had to repalce the in side. time just wasted :cry: