4.0 swap--HELP!!

SPOA87YJ

SPOA87YJ

Well-Known Member
Joined
Oct 28, 2005
Location
Charlotte
I'm swapping a 4.0 from 92 xj into the 87 yj. I pulled the entire harness out of the xj with the motor. We set the 4.0 down in the yj this past weekend and everything was going fine. We starting hooking up all connections and loose ends, PDC and computer all are there. The trouble arises in the ignition. We still can't seem to get the harness's spliced so that it'll start off the key. So far the only way it will start is by jumping it from the battery to the starter wire, and even then it will only run for a few seconds. Were getting fuel to the motor and all, just can't seem to get it to start. Also there are still a few loose connections that haven't been connected. Believe me I've tried, along with the help of others, and we still haven't found where they go. To me, this lies as a variable in the ignition problem. Without all the connections being plugged in, its hard to determine the exact cause of the problem. However, this is my first swap and its all pretty intimidating, but basically all thats holding it back from running is the ignition. Alot of the stuff that isn't connected is most likely irrelevant, but I'm not running the wipers, AC, heater, horn, fan, yada yada off the xj. Anyways, does anybody have an insight on what could be going on? TIA!!!

Austin
 
I have a complete 94 yj engine harness with computer I would sell for $125 let me know and we can work somthin out!

Darrin Vandiver
336-280-8500
 
SPOA87YJ said:
So far the only way it will start is by jumping it from the battery to the starter wire, and even then it will only run for a few seconds. Were getting fuel to the motor and all, just can't seem to get it to start.
Click to expand...
If the engine has been sitting long you may have to replace the injectors. A friend put a 4.0 (that had been sitting about 6 months) in his YJ, and his were so clogged it would barely idle and go dead when you tried to rev it.
 
No trouble with the injectors, ran great before it was pulled. Both xj and yj harness are intact, its the splicing of the two in regards to the ignition thats puzzling. I've got manuals, and diagrams galor, and from what has been tried, we've come up empty handed. Seems like something just isn't hooked up right (which im sure is the case) we just can't seem to put our finger on it...
 
Not for sure 100% but you should be able to hook up this 94 harness to the engine and PLUG it back into the bulkhead connector and it should work no searching for wires or nothin. someone correct me if I'm wrong but, would be an easy solution for a head scratcher!! comes with the 94 ecm.
 
you need a factory wiring diagram, injectors could be getting power from ignition and ground from computer thats why it won't run long, as far as starter wire diagram show you which wire to hook up
 
You need to make sure your injector have power on one side with the key turned on and when cranking becuse some Circuts shut off while cranking. You also need to make sure the computer allways has power with the key in the on and crank posistion.the other side that goes to the computer and it grounds it when the injector fires. this should not be that hard. I think I only had to splice 7 wires when I put the TBI SBC in my J10.
 
painless makes a great harness for this swap. My buddy did the same swap and couldn't get it to run. kept getting a code saying the computer was bad. Got the painless and has had no problems sense.
 
Thanks for the advice guys! I'm completely new to motors, and I guess wiring for that sake. I figured diving in head first I'd come across enough snags to learn something, and obviously I guessed right :). Its hard being up at school cause I can't get my hands on it but I should be able to get home in a few weeks and try and give it another shot.
 
Back
Top