What is this?

[79ramp]

I ran into the same thing when I swapped in the vortec heads and valve covers. I tried finding a pic of where I put it but can't seem to find one. I don't know what it is for though.

I ended up just screwing mine to the firewall when I did the valve covers a while ago, seemed to work. Now that I am doing the motor swap and paying more attention to some of these details, I think I've decided to eliminate it. A little less wiring to clutter my firewall and one less plug to make me wonder 'where the hell does this go to' the next time I work on it lol

I do not think it is part of the cruise control either, from what I can tell in the wiring diagram, it doesn't appear to be connected with any other ancillary systems. My WAG is that is varies the coil power input (...somehow) based on engine speed...not really sure as to the 'why' though.

 

[CorvairGeek]

GM lists it as an engine speed switch. I think it's related to the emissions system, but it could be part of the cruise control too.

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Cool, a picture of one on the side of the 292. My '78 w/T400 didn't have one.

 

[nwalk7800]

Based on the wiring diagram it seems to engage that speed switch solenoid based on engine speed. I'm not sure what that solenoid does, but I would guess it has to do with idle speed or transmission kickdown.

 

[semperfiguy98]

I can help! I have that on my 86 k20 suburban (350,CA emissions)
The relay uses a speed signal from the distributor to activate a solenoid that holds the throttle open a certain amount. To prevent lean backfire when decelerating. The solenoid is mounted where the thermostat housing bolts to the intake and there is an actuator on the carb near the throttle assembly

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[79ramp]

Thought I'd post a quick update: I ended up bypassing and removing this module. It was pretty easy, didn't even have to re-wire anything. Ignition and tach wires were plugged into part of the harness, simply unpluged there and plugged them into the distributor directly. Runs like a champ. Had a bit of a breaking-up issue around 2500 RPM but that seems to have been due to weak springs on the mech advance.