Hello all, I own a '91 YJ with a 4.0 litres HO engine, wich contributes to the greenhouse effect more than a medium size enrergy plant. I bought an engine from a '88 XJ, also MPI, I've drivven the Cherokee so I know the engine is ok. I swapped the engine and everything went smoothly, except one minor thing: The engine won't start. I checked: the ignition, the flywheel, flywheel sensor, the fuel pump and rail. I need to use the motor management system of the YJ and I noticed that a few connectors on the throtlebody don't match. I dont know what they are for. Can anyone tell me where I can find electronical scheduals for those engines? I think there is a problem with a sensor that doesnt give the right signal, or no signal at all, because when I let go of the start key, it seems like the engine wants to start, it bangs a few times and thet stals. Maybe there are other solutions for my problem, or maybe there are conversion sets sold somewhere.
engine swap
Sep 23, 2003
10 Replies
The 88 has a ballast resistor to supply power to the fuel pump when the key is in run. When the key is in start, this resistor is bypassed.
It sits out on the drivers side fender near the rad on the 88 XJ.
Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT'sBert wrote:
Unless its unning rich, burning oil and burning everything else I doubt this very much, if this was the sole reason for swapping to a much earlier engine...well, lets say the tree huggers still won't like you. ;)
An 88 with MPI?? Thought they only had TBI in 88?
Did you swap out the 2 computers? they may be different, since the 91 engine was an HO.
They are different computers for sure.
The 88 runs on the old style, the 91 is the Chrysler version.
The 88 is also a MPI engine.
Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's
Wow..did not know that... learn something new everyday :), mind you most
88's I'm use to were either still carb'ed or TBI (CFI if its a ford).Snow...
They just called it a 4.0 in the Cherokee. The TBI was only on the 4 bangers I think. They went to the 4.0 HO engine in 92 in the Cherokee I think and all the YJ 4.0's were the HO.
The big difference is the computer management system. They are not cross compatible computers.
Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's
As far as I know Bill, they are not interchangeable in any way.
The french computer needs a DRB 11 to get codes, the newer computer is dash codes.
Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's"L.W.(ßill) Hughes III" wrote:
You need to keep the entire 91 wiring harness, sensors, throttle body, distributor, and ignition parts - the easiest thing would probably be to pull the head off the 91, have it gone through (both heads could likely stand a valve job anyway. That way you could keep the manifolds/headers off the 91 and just basically use the block off the
- The throttle bodies are different but look like they will fit. I don't know for sure, but I think they changed the CPS also so I don't know if the 88 CPS and flywheel will work with the Mopar computer. They changed from the Rennix computer to the MOPAR computer in mid-89 or 90 and a lot of the sensors and auxilary parts changed.
BTW, the 91 head/manifold/header will net 20 or more hp over the 88...
No codes are stored in a Renix computer.
Thanks for all the reactions. I think I'll get it fixed this weekend.
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