72 C10 QJet "Solenoid"
 

I have a 72 C10 350/TH350 that came with factory A/C. On my Q-Jet 4bb Carburetor there is a Solenoid that my brother (he has my truck) is sure gets power when the A/C is on. I have just read it's not actually strong enough to move the idle on its own. Only once you push the gas pedal does it keep it the idle higher (or something like that).

When it does get power, it does nothing and appears to be dead? Anyone know the part number or where to get one?

I have read other posts where it is bounced back and forth that it is a "fast idle solenoid" but also some are adamant it is for emissions/anti-dieseling/Curb Idle?

Can anyone tell from my attached photo (hoping to get a closer shot tomorrow).

Re: 72 C10 QJet "Solenoid"
 

It’s for both.
Here’s some that don’t match the year you need but might be adaptable.

https://quadrajetparts.com/quadrajet...c-128_784.html

They are adjustable. Maybe yours is screwed in too far. I’d test with a full 12v before buying another one.

Re: 72 C10 QJet "Solenoid"
 

After downloading the Service Manual PDF - it is a "Idle Stop Solenoid". Emissions Control Systems on page 6T-14

Re: 72 C10 QJet "Solenoid"
 

@geezer#99 they are for both?? Lordy! Guess I need to look at the manual again.

Re: 72 C10 QJet "Solenoid"
 

Used depending on need.
You need it to function as an idle increase because of your a/c.

Re: 72 C10 QJet "Solenoid"
 

Is there any such thing as dieseling of gasoline engines any more with modern gasoline?

Re: 72 C10 QJet "Solenoid"
 

Ah, so you mean one or the other - not both operations (I was wondering how that would work).

I been looking in the Chevy C10 '72 Manual for it to be used for A/C and finding nothing.

Not sure if the engine actually needs it. We just got the A/C completely redone from Evaporator to Condenser. My brother was just sure it was for A/C idle and they are 100% sure its dead. When the engine was out (it was rebuilt too) they tested on the car battery.


Would it have been modified in it's past life by a owner to be for A/C idle or was it actually a factory or perhaps a dealer modification? Just really wanting to know how it was only used originally before any number of owners "adjusted' things :)

Re: 72 C10 QJet "Solenoid"
 

Originally used to set the idle at all times. Then de-energized after turning off ignition and like manual says, plates closed beyond idle. Agree with others that was to prevent dieseling upon shutdown.

Wasn't meant from factory to be related to ac.

Certainly could have been modified to increase idle when ac operational if power was supplied in connection to the ac. Mine is still in place and works. However, I have it disconnected and adjust the idle with traditional method.

Re: 72 C10 QJet "Solenoid"
 

Thank you for your insight!

Under factory setup it seems like a good way to kill you engine when the solenoid goes bad @ idle. Conversely it seems it would likely have a much longer life under A/C operations!

I plan on running med/premium gas, so hopefully dieseling won't even be a problem.

Re: 72 C10 QJet "Solenoid"
 

Exactly, that thing would be energized for long stretches at a time. The engineers were throwing a few stop gap solutions during 70 - 72 with this thing and the TCS vacuum thing.

I have never had an issue with engine run on and like you also use higher octane than needed (mainly to avoid blended fuel).

Re: 72 C10 QJet "Solenoid"
 

If needed could be likely fixed.
I had one apart once. Nothing more than a centre core and power windings around it. Much like a starter solenoid.

Re: 72 C10 QJet "Solenoid"
 

I hear ya geezer#99, I wished my dad was still around - he was great at rebuilding small solenoids - like solenoids for electromagnetic pinball machines. I suppose I should have paid more attention when he was trying to teach me when I was a kid.

Re: 72 C10 QJet "Solenoid"
 

Rich72C10: I looked over mine a while back when I was cleaning mine up. As geezer stated, they are not complicated at all. If the wire varnish is deteriorated it might need replaced (rewound). You can check the wires coming out of the can to see if they are perhaps broken.

If you like, I would offer to try get it back to functional for you. Seems I like tinkering with electronic things.

Re: 72 C10 QJet "Solenoid"
 

Hi Grunther -

I just scored a NOS Carburetor Idle Stop Solenoid GM part number 199746 off eBay. It appears to be the correct one, at least from the photos. With my Amex eBay $30 credit they are running until June, only ~20 bucks. Between shipping to you and back, seems like its a worthwhile try (Seller has been around since 2000 and has high reviews).

I did finally take my off, it appears to been hit or something, the top is a bit busted. Also the plunger is not moving very well and I assume at rest (no power) it should spring back - which it doesn't. So I am not sure it is worth working on.

I tried to get the darn thing opened but I haven't anything to help release the indentions.

Assuming all is well with my "NOS GM 199746" I'm likely to use it to speed up the idle when the AC kicks in :)

Re: 72 C10 QJet "Solenoid"
 

I've got the same solenoid, and it's wired to an unfused always-on-with-ignition blade on the fuse panel. Therefore, always engaged when running, and it kept the idle way higher, regardless of AC on or off. For now I pulled it from the fuse panel.

If it's really just to prevent run on at shut off, then I'll leave it that way. If it's supposed to be to bump the idle when AC is on, why wouldn't it be tied to the AC switch? I posed another thread about it before I saw this one...

Re: 72 C10 QJet "Solenoid"
 

well, its not Factory A/C Idle - I am going to re-wire it for that or at least try it out. If not, then I'll set it up for anti dieseling (which is factory setup).

Re: 72 C10 QJet "Solenoid"
 

Got my NOS GM Solenoid in today and installed per a Factory anti-dieseling. Though now I have to change my habit on starting "warm" to turn on key, tab gas pedal, then turn on engine (as expected).

Which I think the visor starting instruction more or less cover this procedure (without referring to this anti dieseling Solenoid).

It is a very nice NOS part - very happy with it!

Re: 72 C10 QJet "Solenoid"
 

Most of the time that solenoid was not strong enough to increase the ideal speed on its own. It is plenty strong enough to hold the throttle blade open when coming down to idle. But you will still need to touch the gas pedal to set the choke anyway.

Re: 72 C10 QJet "Solenoid"
 

that is true but now I need to touch the pedal after warm up too. Which the visor instructions say anyways :-)

Personally, I just like parts on my truck to work. I suppose it's weird but it makes me happy to look at the carb and know that solenoid is doing something now and not dead LOL!

Re: 72 C10 QJet "Solenoid"
 

Happy for you that you got it working. So, the solenoid was factory on your '72. A/c or no? And, you have the starting instructions on the visor. I wonder if trucks with the factory solenoid are the only trucks with the instructions on the visor (because of the warm start procedure).

Anyway, I also noticed the placement of your throttle return spring...is that factory. Seems to me it is placing a large side load on your throttle shaft which will wear the bore out faster. I always try to ensure the return spring is in line with the throttle cable to minimize radial loads on the throttle shaft.

Re: 72 C10 QJet "Solenoid"
 

That is the factory setup, and yes, you are right about the wear. Millions of them are made that way, including my truck. I have bronze(?) bushings in the throttle body now.

Re: 72 C10 QJet "Solenoid"
 

I am glad Steeveedee knows, as I hadn't a clue - though it was connected just the way the truck came to me.

I wondering if I can have quadrajetpower.com install this "bronze(?) bushings in the throttle body" thing you speak of - my "other" Carb has been in line for a few months waiting for a full rebuild for best performance for my stock-ish engine.

Re: 72 C10 QJet "Solenoid"
 

I know of Mark's fine work from when I used to infest V8Buick.com. You should ask him, but I'm pretty sure he does the bushings (if needed, and they usually are).

Ever since Cliff Ruggles retired, the workload at the other ace rebuilders has increased.

Re: 72 C10 QJet "Solenoid"
 

I suppose you are correct, while it is likely overkill for a stock-ish Qjet, I am having it rebuilt with the performance level 1 option. Crazy backlog, I might get word they are starting on it late April or on May. I guess "Mark" works/runs quadrajetpower?

Though my Solenoid is a bit of a bust. While the Solenoid works great the plunger adjuster is loose as a goose. It just backs itself off and then I have no idle. I have tried some loctite but that didn't work. Having that $30 credit from Amex makes it not so bad.

I am going to try another... not holding out much hope with the one that sold it to me as its a NOS Electrical part.