Intermittent ECU issue? (1 Viewer)

[ShaneA320]

I recently left my 80 sitting for about 3 months while I was out of town, with the battery disconnected.

When I came back and I went to start it; the CEL, charge, and A/T all stayed dark when I turned the key… I knew I was in for a fun time. I went straight to jonheld’s guide after having used it for AFM issues last year. Tested the fusible links, relays, and fuses, they all tested good. Went back and turned the key, what do you know, charge and A/T lights came on (I did nothing other than poke around with the multimeter)

Ok still no cel, next step was to check for 12v at the B+ on the obd connector. It was there, so now I’m thinking ECU itself. Go turn the key just in case, still no CEL.

I figure I’ll try jumping pin 1 and 8 on the connector for the fuel pump, because it’s also mentioned in jonheld’s thing. (Although not really understanding the purpose)

Go turn the key and I have a CEL. Starts fine. Runs fine. Drove it around town for a while. But since I did almost nothing to fix the original problem other than poking around with a multimeter, I’ve lost a bit of trust in the vehicle…

Has anyone had an intermittent problem like this? I don’t really know where to start since I never identified a failed component.

AFM is new as of 6 months ago. Fusible links at the same time. Grounds checked and cleaned then too.

 

[voodu3]

What year is your 80?

 

[voodu3]

I reread. I’m assuming 93 or 94. Pretty sure it’s a failing ecu. Mine did this and I replaced it with a good used one and no more issues.

 

[jonheld]

I recently left my 80 sitting for about 3 months while I was out of town, with the battery disconnected.

When I came back and I went to start it; the CEL, charge, and A/T all stayed dark when I turned the key… I knew I was in for a fun time. I went straight to jonheld’s guide after having used it for AFM issues last year. Tested the fusible links, relays, and fuses, they all tested good. Went back and turned the key, what do you know, charge and A/T lights came on (I did nothing other than poke around with the multimeter)

Ok still no cel, next step was to check for 12v at the B+ on the obd connector. It was there, so now I’m thinking ECU itself. Go turn the key just in case, still no CEL.

I figure I’ll try jumping pin 1 and 8 on the connector for the fuel pump, because it’s also mentioned in jonheld’s thing. (Although not really understanding the purpose)

Go turn the key and I have a CEL. Starts fine. Runs fine. Drove it around town for a while. But since I did almost nothing to fix the original problem other than poking around with a multimeter, I’ve lost a bit of trust in the vehicle…

Has anyone had an intermittent problem like this? I don’t really know where to start since I never identified a failed component.

AFM is new as of 6 months ago. Fusible links at the same time. Grounds checked and cleaned then too.

How about some basic info first. What engine?

 

[ShaneA320]

How about some basic info first. What engine?

Whoops. 91. Unmolested 3FE.

 

[jonheld]

Went back and turned the key, what do you know, charge and A/T lights came on (I did nothing other than poke around with the multimeter)

That sounds like the 7.5 IGN fuse was loose or simply not making contact. The ECU has nothing to do with the CHARGE light or the A/T light, but they're on the same fuse.
The ECU will not "know" that the ignition switch is in the ON position without that fuse, hence no CEL.

 

[ShaneA320]

That sounds like the 7.5 IGN fuse was loose or simply not making contact. The ECU has nothing to do with the CHARGE light or the A/T light, but they're on the same fuse.
The ECU will not "know" that the ignition switch is in the ON position without that fuse, hence no CEL.

Thank you sir. I probably only checked the fuse visually first without removing it; then later removed it to check again once I had gone through everything else and that restored the connection…