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77Jeep
08-09-2023, 05:55 AM
I spent some time going through the disassembly for $42 and it looks like the existing throttle kicker logic can be configured to control an electric fan. The problem is I cannot find a schematic that shows which pin is used to control this.

It's referenced in the '746 disassembly and $99 too, all sharing similar hardware, but it doesnt show up on any schematics I can find online.

Any ideas before I go crazy and start probing outputs?

NomakeWan
08-09-2023, 06:30 AM
As a Corvette guy when I hear "throttle kicker" I think the ASR Motor which physically kicks the throttle pedal to stop you from hooning around, but that's controlled by an ABS computer not the ECM, and I see your ECM has no concept of traction control.

So if by "throttle kicker" you actually mean "IAC," those are shown here in the Outputs section: https://pcmhacking.net/ludis/1228746sheet4.gif

The output pins are "AHI/ALO" and "BHI/BLO" because apparently this particular ECM has a controller for two IACs rather than just one. Not sure what that's about.

77Jeep
08-09-2023, 07:44 AM
its a vacuum solenoid that operated a plunger to physically kick open the throttle shaft. I've never seen one in the wild, but its in the disassembled code at ld008 for all mentioned ecus

the eprom settings are tps off, temp on, temp off, enable, and invert output. It also doesnt look like it's intertwined with any other functions. Perfect for fan control, I just cant find the physical output. Guess I need to do some more code tracing

NomakeWan
08-09-2023, 12:26 PM
Possible it's that secondary IAC?

I mean, unless one of these vehicles actually has two separate IACs.

steveo
08-09-2023, 05:47 PM
i think the only thing gm ever put dual iacs on was the crossfire

udidwht
08-13-2023, 03:45 PM
The 454 trucks had them...

http://www.gearhead-efi.com/Fuel-Injection/attachment.php?attachmentid=19037&d=1682954760

https://www.youtube.com/shorts/eftF_v-RurY

It's purpose was meant to hold the throttle slightly open for the first cold start preventing the throttle butterfly from binding.