Working on a friend's '89 IROC (5.7 TPI). I cannot adjust idle speed because I cannot ground the ECM via the ALDL diagnostics port. I checked for voltage, which is 4.96 at the ECM and terminal B at the ALDL. GM spec for this is 5 volts. Ground for this circuit is 3k. I've tried everything to ground the ECM with no response. I'm thinking it's inside the ECM. The fans also don't work (duals)...I checked at the relays and the A/C pressure sensor and they work OK. Am I looking at an ECM malfunction? He doesn't have the $$$ for a new ECM. I had somewhat similar problems on my '86, but it would go into diag mode, but not communicate with a scan tool (GM tech1). Anybody have problems with this? I can't figure out what else to test. I'm hoping it's a wiring problem (it's obviously been tampered with). Any help would be appreciated -dhirocz

 

Are you jumping A and B on the ALDL? Top row, far two on the right? I can find the ALDL ground to the ECM when i get home for you...you can then check continuity of the wiring.

Also, may be a good idea to check the grounds on the rear of the heads too, make sure the connection/contact points are clean and tight.

 

Yeah, I'm jumping the right ones, with no response from the ECM. I was told the grounds were good but I'll check them myself. I traced the two wires from the ALDL to the ECM and tried to jump it there, with no response. That's why I'm thinking the problem's ECM related. External grounds may cause the problem through another circuit inside the ECM. I'm hoping it's not a QDR failure inside the ECM, which would explain why several other things don't work. I'll keep looking...