Having some runability issues. Jeep starts fine and idles but if you give it any throttle in falls on its face and pop. While doing many other tests on all of the sensors and wiring i found that the wiring to the injectors were in the wrong spots according to two different schematics. #3 and #4 were swapped and so were #5 and #6. Put them back to the wiring diagram and it still runs the exact same. Does this indicate a computer issue? I also noticed it has a computer in it out of a manual jeep and mine is an auto. Background I bought this jeep not running and according to the vin it had a 4cyl in it from the factory but has all of the correct tags and stickers under the hood for the 6cyl. Any info would be greatly appreciated.

 

I am inferring that you have an auto trans in it? I think I'd start by tracing your leads once more and checking again. Also check your plug wires while you're at it. In fact, a full tune up with new wires, dist cap, and plugs couldn't hurt. Check the color and gap of the plugs and see if anything looks amiss. Lastly, it could be a bad fuel pump, check the fuel pressure at the rail with a kit you can rent from the auto parts store.

 

The 4.0 ECUs are interchangeable 87 to 90,

You are likely starving for fuel. Do a fuel pressure test.
Fresh tune up parts can never hurt.

 

Cruiser - is that true between the Autos and the Manual ECUs as well? I thought I remembered reading somewhere that they were different in some way.

 

You would never notice the difference between manual and auto.
You will notice the difference using an 89 or 90 ECU in a 1988 or 1987.

 

Fuel pressure is at 31, 39 with the pressure regulator vacuum line pulled. All of the sensors have been tested. All of the plugs, wires, cap, rotor, coil, and distributor have been replaced. I also went through the setup of the distributor you sent me on another thread. Fuel filters have been replaced. Fuel tank has been removed and cleaned. I have even ohmed out the wiring for the injectors back to the ecm.

 

what happens if you rev it up with the fuel pressure tester hooked up?

 

When throttled up it will go up a bit then level back off at 31.

 

Classic low fuel delivery symptoms but passes that test.

I take it you have visited my website. Which Tips have you completed?

 

I had only looked at the distributor indexing tip. If the weather holds out tomorrow I will go out and go through all the other tips and let you know.

 

1,3,4, and 5 first. No shortcuts.

 

You're not joking there. I upgraded from my '87 ECU to an '89 or '90 and it's a noticable difference. Btw, is there a way to tell what year it's from by the serial number? I simply cannot recall what year it's from and I'd like to know. It may even be from an '88?

And to the original poster; don't be intimated by doing the C101 connector elimination. I avoided it for *years* and just recently did it. It's really really not that bad and I'm glad I did it even though I want really having any issues at the moment, it's one less thing to have on the "worry about" list.

 

Best to get one from a 90. Ends in 428 or 429.

 

I have been looking on here for years for information about my xj and found a lot. Follow Cruiser's tips, I printed them out and keep them in repair manual. Do them first, I had a problem a few years back, did all the tips and it helped. A year ago I had something like what sounds like you have, replaced a lot parts and still not improvement. Found Nick who makes a Renix engine monitor (REM) bought one and it helped me find that the MAP sensor that I got new was bad. Hope that helps

 

Did 1, 3, 4, and 5. Did the cps test and I'm only getting .135v ac. I will try and adjust it if not the local Napa has one in stock and I will replace it.