wanderlust_cherokee

Replacing the ecu in my 92 Cherokee Laredo, any advice highly appreciated !

Replacing the computer because the Jeep would not start- starter, fuel pump, and battery all all fine supposedly.

This is actually the second try, the computer that the mechanic replaced went out after driving it to return the core the next day. 🙃

Cummins93

https://www.cherokeeforum.com/f2/99-...-tests-221715/

Test for spark trigger.

Verify the injectors are firing while cranking the engine.

lawsoncl

It's pretty rare for the ECU to go bad. Two bad ones tells me your problem is elsewhere. Crank position sensor is pretty high on the list of things I'd suspect.

wanderlust_cherokee

So, replaced the ecu and got it all back together. Waited 10 minutes until I connected the battery. Then I left it on for five minutes in accessory mode before starting it.

I got it to turn on! did a loop around the block and then got home and parked. Turned it off and it did not turn back on.

For reference it has a new starter, the fuel pump still sounds, it’ll do accessory mode but it won’t crank.

This is my first major repair done completely by myself and all I’ve got is a socket wrench set an a 10 mm wrench so feel free to use simple terms, still learning.

wanderlust_cherokee

Any advice on how to check for that or could you send me a thread?

lawsoncl

By "won't crack", do you mean the starter won't spin or it spins but the engine never fires? Is everything else normal with the key in the run position, hvac, etc? That might point to a bad ignition switch. If it's not cranking at all when you turn the key to start, try jiggling the shifter or starting in neutral. If that works, then it's the NSS.

wanderlust_cherokee

So by “won’t crank” I guess I mean that it’ll buzz and all the lights work, but that when I turn the key all the way it’s just silence.

I tried the starting in neutral trick and it didn’t work this time (I got the transmission rebuilt back in 2020 April).

The mechanic who told me to replace the computer suggested that it could be some of the wiring shorting out the computer, but I would have no idea how to start with all that

lawsoncl

The starter not spinning the engine when you turn the key is definitely not the computer. Suspects would be the NSS, ignition switch, starter relay, bad ground connection somewhere, etc. I would not trust any mechanic who immediately jumped to the engine computer for a no-crank situation.