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87 yj 4.2 to 89 xj 4.0 wiring help

6K views 9 replies 5 participants last post by  JeepElliott 
#1 ·
I have a 87 yj with the 4.2 carb, I'm swapping to the renix 4.0, which I got the whole jeep for 150 so I couldn't pass up the deal. I have swapped the engine to the yj but in desperate need of help on the wiring. I have searched and searched and now even more confused than before.

If anyone can help me with the wiring I would greatly appreciate it, lots of pictures help. I know I need a external fuel pump but after that I'm lost. Please help its been 1 month since I have drove my jeep since the start of this mission.

Edit: I also live in CA
 
#3 ·
What did the donor engine come out of?

Do you have the factory service electrical manual for the donor engine?

I'll bet you need just about everything out of the donor. Hope it wasnt an xj.
 
#5 ·
Most of the xj harness is different. You cant even swap the fuel pump system, iirc. You need alot of stuff from a yj but they only had renix for the 2.5l

You are going to need fsm wiring diagrams from all involved.
 
#6 ·
Having the wiring diagrams will be your salvation as DREDnot stated, then when you get done using them, sell the one/s you don't need.
I think I know the answer but I'll ask anyway;
Did you, by chance, label the wires/lines/cables as you removed the motors???
(I just went thru this several months ago with my 69 dart swinger project, swapping in a 5.9mag from a 99 ram. I spent about 2 days (no joke) TWO days (about 20hrs) doing nothing but labeling every single line I disconnected, that plus the FSM wiring book has me covered for 90+% of my wiring. I learned this lesson the hard way years ago.)
I'll assume you didn't label anything because most folks think a jeep is jeep so wiring is the same-unfortunately, not the case.
I would recommend you get on a few cherokee forums since they'll have a better knowledge base for the xj than most of us here. But you'll still need the FSM 's.
Start by labeling/eliminating the obvious stuff and go on from there. The good news is; you still have the donor xj, so you'll be able to match/label/coordinate the various wiring, it'll be a long, tedious process, but you've def got a leg-up right there.
Wish I could help and Sorry that I'm not of any actual wiring assistance.
 
#7 ·
I have everything hooked up with the engine, just need to find out what wire/wires I need to take and plug into my yj bulkhead to make run.

I did label wires on both engines before I disconnected it all so that was simple part, I just know that there are a couple that I need to plug in the bulkhead and that's where I'm lost.
 
#8 ·
When i did the 4.2 carbed to 4.2 with 4.0HO head and fuel injection conversion, i chopped the YJ harness about a foot down the lines and took both (YJ and XJ) harness and used the wiring diagrams for each to match the wires, took some time but it is possible with some work. Look up the 4.2 to 4.0 EFI conversion and it should have the minimum wires to get it running. You only need 5 wires to get it to fire.

4.2L Fuel Injection and Build - JeepForum.com
 
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