What is the best way to test the ECM to see if it is working correctly?

[Oberst Oswald]

What years are the two jeeps? What color are the keys of the two jeeps? What transmission is in the two jeeps?
What engines are in the two jeeps?
If the keys are gray they have a skim unit and won’t swap.
If the transmissions are both manual or both autos they will swap.
Gotta be both 4 bangers or six.
Years…..meh.

1999, manual trans, non skim, 4.0L engine, non ABS brakes... this is the Jeep with the problem

1997, manual trans, non skim, 4.0L engine, ABS brakes... Jeep runs but unused.

 

[Oberst Oswald]

Plug in an ODB scanner and see if you can communicate with the PCM.

-Mac

Bought a Launch C reader Professional 123Xl V2.0 . Will see if this helps me out but since the Jeep is not throwing any codes, with my luck, I doubt it.

 

[TJ Jim]

1999, manual trans, non skim, 4.0L engine, non ABS brakes... this is the Jeep with the problem

1997, manual trans, non skim, 4.0L engine, ABS brakes... Jeep runs but unused.

I’d swap it

 

[Oberst Oswald]

I’d swap it

I agree. Just want to know if the swap will start the Jeep or at least give some codes.

 

[TJ Jim]

One easy way to find out.

 

[Oberst Oswald]

Success... but more like dumb luck than brains. OBD scanner didn't show anything that important (high voltage to fuel gauge) that would keep the engine from starting. Checked fuses, relays & grounds. OK. Switched PCM with the one from 1997. No difference except no high voltage to fuel gauge code. Now the dashboard "check gauge light" came on. Switched back to 1999 PCM. OBD scanner now says everything fine. Still won't start and not hearing new fuel pump running. Ready to give up and suggested maybe think about "sending it to the man". That went over like a lead balloon. I'm still on the hook to pull a rabbit out of my hat so decided to remove the plastic wire loom covering off the wires leading to the fuel pump & gauge sending unit. There it was... the original owner did splices to the 4 wires going to the fuel pump plug about 1 1/2 feet up under the loom covering which had wires melted & the positive lead broken ever so slightly. Redone the splices, pump hummed & the sound of a running Jeep filled the air. Went for a ride and my son was glad that I was his Dad.