1991 YJ body with 1990 4.2 Engine Swap Wiring

[Kiltedbiker]

It has been a nightmare to try to trace down and match up the wiring for this 4.2 engine to mate up with a body made for a 2.5L L4 OHV 8V. the brackets were ground off the frame and relocated, then welded. I am trying to get the wiring to mesh up with the dash, A/C, etc. It appears that Jeep sends all of the power from the engine to the head light switch. I am lost and can't find a wiring harness for the dash. Anyone have experience making this conversion work?:???:

 

[Bounty__Hunter]

Were you aware the MPFI 2.5L engine you removed is rated at a higher horsepower than the carb'd 4.2L you're replacing it with?

I don't have any info on making the wiring work, but I'm about ready to dive into two swaps using the GM 4.3L to replace 4bangers.

 

[Kiltedbiker]

No. The engine was one taken out of my last YJ. I didn't need to do research, I had the engine. The price was right.

 

[superj]

I have no idea but I think all the gauges have to be replaced because the carb'd motor reads off sensors well the fuel injected sensors go through the computer and then to the gauges, especially the speedometer.

I think, so keep an eye out for info on the gauges

 

[jps4jeep]

I have no idea but I think all the gauges have to be replaced because the carb'd motor reads off sensors well the fuel injected sensors go through the computer and then to the gauges, especially the speedometer.

I think, so keep an eye out for info on the gauges

^^this^^

your trying to put a carbed engine into a wiring harness with EFI, there are a lot of pins you will need to eliminate. Just to break it down in basic terminology, your 4.2 needs 3 things to run; ignition, fuel and spark. the EFI motor's harness had provisions for those plus TPS, CPS, O2 sensor etc.. if you took the free motor out of your old YJ, then get the free wiring harness from the old jeep and put it into the new one.

 

[elevatorman]

I agree with Johnny,utilize your old harness as well.You will have less electrical headaches and a more reliable jeep when done.

 

[Kiltedbiker]

I agree with Johnny, too, but that harness left with the Jeep. Because my insurance company totaled it and it cold only get a 'salvage title', it was no longer road worthy, so I sold it for $200. He got a deal to make an articulated off-road vehicle. I was hoping to find someone with the experience to share their wisdom of how to match the Engine and dash harnesses at the firewall and whatever other changes needed to be made.

 

[jps4jeep]

You need to pin out the harness, adn there is no way in hell I can give you a detail description on how to do it on here, it would be a 6 page post.

basically you need the wiring diagram for the dash and for the engine bay for both vehicles, start with what the 4.2 needs, then what the accessories need. then see what the 2.5 had and you don't need, you need to remove the PIN from the bulk head harness for the fuse block or the ECM. some things simply won't work like the speedo. the 2.5 used a VSS and the 4.2 used a cable. you will need to swap T-cases or convert the speedo.

You have your work ahead of you. I've pinned out more harnesses than I would like to admit and on average, to do it properly and cleanly so it look professional should take you about a week working couple hours a night after work. Honestly, you can probably do it quicker since you will be removing more terminals than adding.