4.0 swap guys please help.

[yodaman1151]

Bought an 85 that had a 2.9 and someone swapped in a 4.0 they did an extremely terrible job and I've had to chase several things down to get it to run... My question is: if I get a dash and the cab and under hood harness' should I only have to splice the lighting and fuel pump wires? I did a lot of searching and didn't find anything that answered my question. It's all manual everything.
Just FYI it runs terrible while cold and I can get it to run decent while warm but the iacv has to be unplugged or else it idles really high and the temp gauge doesn't work so im thinking the computer doesn't know the engine temp and it doesn't charge either. But instead of trying to track down wires in this birds nest I want to start fresh

 

[DgafDunham]

when i swapped complete harnesses (from 2.9 to 4.0) in my 90 ranger from a 93 explorer the only wires i had to splice were the fuel pump and lighting wires that run through the frame on the drivers side, also i believe there was a wire i had to jump on a connector on the drivers pillar to get my dash lights and ish to work correctly.

 

[Downey]

i think you only need to swap the engine harness but i could be wrong i dont think you need to swap the cab harness.

 

[swamprat]

Do you know what year the 4.0 is? If the comp doesnt know engine temp then it will run rough when cold. Temp sensor is either not plug up or wires dont make it to the comp. Is this engine or the harness out of an auto (4.0) truck? Could be why it idles high. Mine did.

If I was you here is what I would do.
verify year of engine
verify what harness is used, egine and body
make a list of problems(temp guage)
fix one issue at a time, dont try to fix it all at one time, just over whelm yourself

 

[yodaman1151]

That's what I'm thinking but I plan on ripping everything but the rear lighting harness out of the junkyard. Just basically wire the whole thing from the cab and firewall forward

I'm told it's out of a 91 ranger. They used the fuel sender and **ger rigged the lines together so it was getting only 24psi at the rail. I put a frame pump from an older truck inline and got it to have enough fuel to run. I gotta check the comp but I'm sure it's right.
I want to re do the wiring cuz it's a serious fire hazard how it's done now

 

[yodaman1151]

I want the newer dash too so I just figure it will be easier to redo most of the wiring at the same time. Should I look for an 89-91 truck for the harness and dash or just a 91 to match the motor?

 

[swamprat]

not familiar with an 85. Might just be easier just to swap out dash and wire from a 91. Just about every year had a small change in wire harness. If you can find a 91 get it.

 

[yodaman1151]

I probably won't get to it for a couple weeks cuz I got bills but I mainly just wanted to get a little input. I'll get pics of the rats nest that is in there when I go work on it again