90 XJ gremilins

I have been fighting a gremilin on my daugthers 90 XJ, sometimes when
she cranks it it will run on only 3 cyl . if she turns it off and
restarts it runs fine . the problem has gotten worse recently , I had
the jeep today and it was running on only 5 cyl so I pulled the
injector plugs to diagnose which cyl was missing I found number 5 cyl
with no injector pulse . I pulled the ecu and found no signal from the
ecu to the injector. so I figure bad ecu, then I turn the jeep off and
restart and wala all 6 firing .
I think it's the 268,000 mile ecu dieing anyone else have an issue like
this ? any opinion on declareing the ecu the culprit?

I would start by cleaning all of your connecters and grounds first and see what happens. This is a common problem on older XJ's. My 90 is acting strangely again as well so its time for another cleaning!

I can say its rare for the 90 and earlier ECU's to fail but it has happened to some people( I think). I can't pin point it but other people will be along to help.
Untill then try the search methods on RENIX engines these are the engines in the pre 91 era and have very sensitive electronics.

xjtrailrider said:

I would start by cleaning all of your connecters and grounds first and see what happens. This is a common problem on older XJ's. My 90 is acting strangely again as well so its time for another cleaning!

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there is no conector between the ecu and the injector except for the injector plug and the ecu itself , ad both of them are clean as a whistle

I pined the ecu at the wire plug and got nothing thats why I thin the ecu is going south.

I think it was lawsoncl and 5-90 and a few others were helping a guy in eastern Europe (Croatia?) about 4 weeks ago replace a bad injector firing transistor on the ECU.

The Renix ECU is pretty bullet proof, but there have been 2 that failed that I know of, 5-90 has one of them, and the guy in Eastern Europe had the other but he fixed his with about $1 transistor. The details are right here in a thread from about 4 to 8 weeks ago IIRC.