'90Cherokee

The injector works fine, connected #6 plug to it to verify. Ground at the plug is good. I cut the loom open from the injector to the big plug on the firewall and the wires appear to be fine. I also loosened and wiggled the big connector on the firewall with the engine running and heard no change. I disconnected that connector and nothing looks obviously bad. I'm thinking maybe the ECU, but want to know what else I should check.

Also, would the ECU from my '90 work on the '87? If so I could swap them and see to know if it's that; assuming the ECU isn't a ***** to swap, I haven't investigated that at all.

This XJ is new to me and I have no related history other than the PO having done a Bosh injector swap. He apparently didn't even realize that this cylinder was not firing so not much to go on.

cruiser54

You lost an injector driver in the ECU.

Get an ECU out of an 89 or 90 and get some more pep out of your Jeep.

'90Cherokee

That's what I was guessing. What does the later computer do to give it more pep? Are they the same for manual & auto? This has a manual but may have been a conversion. If I jumper the power from another injector will it be instant death to that driver? I wanna be able to drive it once at full power to test things out before putting more $ into the thing.

fb97xj1

I would think that jumping the power from one injector to another will result in two injectors firing at the exact same time.

'90Cherokee

They will, and while not ideal it's much better than no fuel to that cylinder.

cruiser54

I don't know exactly what they do, but they do it.

My experience with losing injector drivers is that they can just fail for who knows why.

Or, they can fail because that injector is shorted. Be careful monkeying around with the wires.

I think you found the problem and did an excellent job doing so.