Engine Swap Help. Need some advise

I have been hanging on to my ’91 jeep that was totaled for a little over a year because it had a rebuilt motor, Trany, and regeared T-case that I planed to swap into my ’88 that has a tired motor.

I know it would be a challenge because my ’88 is a manual and my ’91 is an automatic. (I know many of you are yelling at me right now about switching to an auto, but after wheeling with an auto with a gear selector that is how I prefer to wheel) So now I finally have the money to swap the drive train and I find out that in ’91 they switched to the Chrysler electrical, and engine management system.

My question is this. Can I put the engine (4.0), Trany (AW4), and transfer case (NP231) out of the ’91 into my ’88? I am going to scrap the ’91 when it is done so I can take as much or as little as I need to out of it, but I don’t know if I want to try to rewire the whole jeep.

You will need a TCU for the automatic, so either you go '91 electronics or you need a older TCU. I think you would have to retrofit some parts including distributor to the '91 to stay RENIX. The only wiring changes should be in the engine compartment to go all '91. Now you get the RENIX freaks (term of endearment, not criticism) who love the old stuff and then the other side.

winterbeater said:

You will need a TCU for the automatic, so either you go '91 electronics or you need a older TCU. I think you would have to retrofit some parts including distributor to the '91 to stay RENIX. The only wiring changes should be in the engine compartment to go all '91. Now you get the RENIX freaks (term of endearment, not criticism) who love the old stuff and then the other side.

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Thx for the reply. I planed on using the TCU out of the '91 but the ECU is what has me a bit worried. I guess I should look and see how much wiring I would need to swap. I know the dash cluster is different on the '91 as it has a electronic Spedo and the idiot lights are all in diffrent places. but beond that I'm not sure how much would have to be replaced.

You won't want to swap the computer and wiring, as you would need to swap ALL of it. You will want to make the HO motor run on the Renix computer system. This involves swapping all the Renix sensors onto the HO motor. You will need the Renix alternator, and the transmission flexplate. It will not run without the Renix flywheel/flexplate, so you will eiter have to use the manual, or buy a Renix flexplate for the AW4. You also will need to use the Renix intake and TB, or else adapt the Renix TPS to work with the HO TB. Adapting the TPS is the hardest part of the swap, there is a kit available, but I've never seen it. You'll probably want the Renix injectors as well, mine seems to run rich with HO injectors. I tried to use the guages but I could not get the electric speedo or tach to work without its computer.

Renixing an HO is easier than swapping the entire wire harness, and Renix freaks such as myself will tell you that the Renix system is better. Good luck.

Doesn't the TCU need input from the ECM (PCM)? The TCU also needs input from the TPS. To go RENIX, wouldn't he also need a RENIX compatable TCU?

So would it be better to just run the motor until it die's and put a aftermarket AT in (like maybe a 700R4) in the meantime? Spend the money on upgrades instead, then rebuild the engine when it dies. (stroker)

Slip Kid said:

You won't want to swap the computer and wiring, as you would need to swap ALL of it. You will want to make the HO motor run on the Renix computer system. This involves swapping all the Renix sensors onto the HO motor. You will need the Renix alternator, and the transmission flexplate. ......
Renixing an HO is easier than swapping the entire wire harness, and Renix freaks such as myself will tell you that the Renix system is better. Good luck.

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Slip Kid, it sounds like you have done it. How much of a pain in the #$% was it? I guess the simpler question is is it worth it?

It's worth it. The only hard part is adapting the TPS, if you don't use the old intake. I'm pretty sure the TCU does not involve the ECU at all for those years. I know that the HO TCU will not plug into the wireing for the Renix TCU. Getting the TCU wired up might be the difficult part for you, you'll need a Renix factory service manual. Who knows what a renix flexplate will cost from the dealer, or if they even have one. I'd just put the manual in it. :roflmao:

I guess either way you would want the newer axles, as the autos are geared lower. unless the 88 has a 44 of course.

Slip Kid said:

It's worth it. The only hard part is adapting the TPS, if you don't use the old intake. I'm pretty sure the TCU does not involve the ECU at all for those years. I know that the HO TCU will not plug into the wireing for the Renix TCU. Getting the TCU wired up might be the difficult part for you, you'll need a Renix factory service manual. Who knows what a renix flexplate will cost from the dealer, or if they even have one. I'd just put the manual in it. :roflmao:

I guess either way you would want the newer axles, as the autos are geared lower. unless the 88 has a 44 of course.

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I already re-geared the front and rear and drooped in some alloy axles shafts, as I do have a 44. Maybe If I put in a hand throttle I wouldn't mind the manual as much but I just find it soooo much easier to wheel with a AT. I know; driver error.

Anyway after doing more research I think the way to go is to just use the block out of the '91 and keep everything else from the '89 (even swapping the intake seems like a pain) Although it does appear that the Renix blocks are the way to go for a stroker due to the Knock sensor.

So many choices. Anyone want to buy a 25k mile '91 4.0 and AW4?

The head and intake are the better parts on the HO. I've also heard renix blocks are better. You will have to tap a hole to put the knock sensor in the HO. The hole itself was already there on mine, just had to tap. It's an odd thread size IIRC.