Hi All,

I was working on getting my electric fans running again (89 Chevy TPI 5.7), and had the car in the paper clip mode, so I would be able to trouble shoot. Anyways I noticed (now that the noise from the fans was gone) the IAC motor was stepping continuously. This was obvious from the sound comming from the IAC. This doesnt seem to make much sense, especially with the engine off. Is this a caveat of the test mode or is this a sign I need to replace my IAC or another sensor? I did get the fans working, one of the connectors was dropping 5 volts accross it! Any info is appreciated.

Thanks,
Martin

 

You are correct. The ECM will continue to phase/step the IAC toward the closed position when in Field Service Mode. Since the ECM has no direct feedback from the IAC, it just continues to step. If the engine were running, the distributor reference pulses (RPM) signal to the ECM would provide the necessary feedback to regulate the IAC.

Since it's bothing you, unplug it while you get the fans running. Or ignore it, now that you know it is normal.

The primary fan should energize based on the AC input or CTS input. If you unplug the AC high pressure switch with the ignition on, the fan should run. The secondary fan temperature switch is installed in the right cylinder head.

 

Thanks Vader, that answers it. I figured that made sense, that the ECM doesnt have the normal feedback loop as if the engine were running. I didnt think the engineers would set it up so that it runs continuously, but it makes sense that it doesnt hurt anything.

Thanks Again,
Martin