Solenoid on q-jet

[Sport/Truck]

What is this solenoid for and is it necessary? My truck is a non ac truck, my first guess was it was to kick up the idle when the AC is on.

s/t

[dwcsr]

It an anti dieseling device. You actually set the idle with that and set the screw to where its just about closed.

[Sport/Truck]

So, not all trucks got one?
s/t

[Wrenchbender Ret]

It looks like a idle control for an early partial computer control. If the carb has no other electronics except choke you can use the carb & remove the selenoid or use it for A/c kickup or anti deisel. I didn't see any other elec. sensors in the photo.

[Sport/Truck]

Originally Posted by Wrenchbender Ret

It looks like a idle control for an early partial computer control. If the carb has no other electronics except choke you can use the carb & remove the selenoid or use it for A/c kickup or anti deisel. I didn't see any other elec. sensors in the photo.

Correct, there are no other electronic controls on the carb. This is also the original carb too. What would cause it to have an anti dieseling device installed from factory?
The only other explanation I can come up with is the fact the engine (although original for this truck) was actually supposed to be used in another truck (going by the stamp on the block). But since my truck was one of the first to roll off the line in ’71 it got some left over parts.

My buddy has an original ‘71 GMC Suburban with AC…and it doesn’t have the solenoid. This is why it’s confusing to me. So the anti dieseling solenoid make sense, but what determined the use of such a valve, I mean this has the factory wiring and everything.
s/t

[Wrenchbender Ret]

Some of the early emission control systems used a high idle speed & lean idle mixtures to qualify. That made a solenoid necessary to prevent run on. It might be a California truck.

[Sport/Truck]

Originally Posted by Wrenchbender Ret

Some of the early emission control systems used a high idle speed & lean idle mixtures to qualify. That made a solenoid necessary to prevent run on. It might be a California truck.

Not a California truck; ordered and delivered in Colorado. ( I have the papers when he ordered it, and the papers when he took delivery) My buddy’s Suburban was ordered in New Mexico and it doesn’t have the solenoid.
It really doesn’t make sense.
s/t

[GMCPaul]

Its a transmission spark control solenoid. Used on some 69's and all 1970-1972 trucks to our knowledge.
GMCPaul

[Sport/Truck]

Thanks! Is there anything special I need to do to remove this system? I already omitted the two relays off the drivers side fire wall. (I hope its to be a big deal to remove all this).
s/t

You said all 70-72 trucks to your knowledge.... Does this include the Suburbans?
s/t

[GMCPaul]

Just pull it and your done nothing special needs done, it was used on all C/K ( Truck, Panel Truck, Suburban, Blazer & Jimmy ) vehicles from 70-72 and was probably the first item most owners & shops removed.
Your lucky if you see 1 in 40 trucks with it still attached to the carb but disconnected and rarer yet maybe 1 in every couple of hundred will actually have it still all connected to carb and wiring.
GMCPaul

[70c10]

I sold one on ebay a few years ago and got more than I thought I would!

[Sport/Truck]

Originally Posted by 70c10

I sold one on ebay a few years ago and got more than I thought I would!

Interesting idea
s/t

[RustyParts]

I think Its purpose is to keep the engine idle speed the same with or without the air conditioner on. If the engine idle is set at 600 rpm with the air conditioner off and you turn on the air conditioner the compressor load would drop the idle speed down. This solenoid would return the idle speed to normal by extending a shaft to open the carb plates. It was adjusted with the air conditioner compressor turned on by screwing the shaft of the solenoid in or out. Can also be used as a anti dieseling device on vehicles without air by setting the rpm using the solenoid instead of the carb idle screw so when it de-energizes the carb plates completely close.