Author Topic: Idle step up solenoid bracket for Q-Jet  (Read 114 times)

cyber104

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Idle step up solenoid bracket for Q-Jet
« on: July 22, 2021, 04:25:16 AM »
Hi All:

After an exhaustive online search I still cannot come up with a bracket to hold a small solenoid to boost my idle when the AC is on.

This solenoid and bracket may also have been used in "reverse" (to drop the idle off when the ignition was switched off) to prevent engine "run on"

I run the original R12 system with an A6 compressor which pulls the idle down almost 300 RPM when it's running.

Thanks - any thoughts or sources would be most welcome
1978 TA 4-Speed W72

firebirdparts

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Re: Idle step up solenoid bracket for Q-Jet
« Reply #1 on: July 22, 2021, 08:49:56 AM »
They ought to be common as dirt used.  Practically everything was air conditioned.  Is this a more-or-less original configuration?  What's the original carb application?

I would have one, I think, for a late 70's 400.
I want to be like Paul Kenny when I grow up
Joe Bays
1977 Y82 4-speed (red interior)
1978 Skybird 350
1978 Redbird 305
1979 Redbird 301 4-speed
1992 Lincoln Mark VII LSC/SE (red)
1970 Datsun Pickup
1953 Chevy pickup (converted 4x4)
1988 T-bird Turbo Coupe

cyber104

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Re: Idle step up solenoid bracket for Q-Jet
« Reply #2 on: July 22, 2021, 08:55:05 AM »
Completely stock setup - both AC and  Q-jet are original to the car which is a 1978 with Pontiac 400.

If you have something that would work I would be very grateful - I just can't seem to find anything

Thanks much
Chris
1978 TA 4-Speed W72

pancho400cid

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Re: Idle step up solenoid bracket for Q-Jet
« Reply #3 on: July 22, 2021, 03:25:51 PM »
Not sure what year etc. your car is.

Below is a picture of the carb/bracket/solenoid for my 78 Trans Am with L78 400.  I think this is the bracket & solenoid we are talking about?

1978 Trans Am - Chesterfield Brown - current project
1978 Trans Am - Silver - SOLD!

tajoe

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Re: Idle step up solenoid bracket for Q-Jet
« Reply #4 on: July 22, 2021, 06:19:29 PM »
Panch shows a good picture. Is that the bracket you're looking for? Does it have-ta be exactly that? I have years of Q-jet scrounge, and probably also  have some brackets. Try and find a picture of the exact one, and I'll bet one of us has one.
"You can sell an old man a young mans car,
but you can't sell a young man an old mans car"
                                       Bunkie Knudsen

Re: Idle step up solenoid bracket for Q-Jet
« Reply #4 on: July 22, 2021, 06:19:29 PM »

firebirdparts

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Re: Idle step up solenoid bracket for Q-Jet
« Reply #5 on: July 23, 2021, 10:47:14 AM »
77 is the same based on what I see here in the shop.
I want to be like Paul Kenny when I grow up
Joe Bays
1977 Y82 4-speed (red interior)
1978 Skybird 350
1978 Redbird 305
1979 Redbird 301 4-speed
1992 Lincoln Mark VII LSC/SE (red)
1970 Datsun Pickup
1953 Chevy pickup (converted 4x4)
1988 T-bird Turbo Coupe

Wallington

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Re: Idle step up solenoid bracket for Q-Jet
« Reply #6 on: July 23, 2021, 08:17:14 PM »
This solenoid and bracket may also have been used in "reverse" (to drop the idle off when the ignition was switched off) to prevent engine "run on"

That's how most of these operated on Quadrajets on Australian delivered V8's. Strangely enough in a hot country, the 70-90's era barely featured aircon, unlike the US. And these solenoids were set to idle speed with power on, and dropped out when key ignition turned off, effectively stalling the car. This prevented run-on or dieseling, ironically, another feature of a hot engine in a hot country, that said no to aircon but yes to annoying engine symptoms after a long trip.

Like others have said, even if you just come up with the bracket, you can often adapt different solenoids to suit. Likewise, half the guys with aircon disconnected or removed possibly still have it installed without a use.

cyber104

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Re: Idle step up solenoid bracket for Q-Jet
« Reply #7 on: Today at 03:55:34 AM »
Well I did manage to source 2 different solenoid/bracket assemblies.  The one is similar to the one shown in the picture above.  The interesting thing is that this solenoid does not have enough power to "idle up" the engine.  I believe it is more suited to "drop out".  The reason I say this is that if you energize it - it is not strong enough to push the throttle linkage.  However, if you push the throttle linkage forward manually a bit - the solenoid is able to "click" and once it is locked fully extended it has plenty of holding power.

My thinking is that the one I have is designed to hold the idle until the ignition is shut off - and it is initially "set" by turning on the key and pumping the gas pedal (like we all do before starting with a Q-Jet).

I have also demonstrated this on my workbench using a 12V source.  Initially I can easily keep the plunger depressed with my thumb.  Remove my thumb and the plunger extends fully and clicks/locks into place.  Once it is in that position and energized I cannot press it back in.

I suppose I could use this type of solenoid with my AC.  But my plan was to have it energize only when the compressor is running.  If I go with this solenoid, if the compressor kicks off, the plunger will retract and not have enough power to raise the idle when the compressor comes back on - unless I blip the throttle to allow the plunger to extend and lock again.

Panch - are you sure your solenoid is raising the idle?  Maybe it's the "drop out" feature.

I suppose it's also possible that the solenoid I have is old and weak.
« Last Edit: Today at 03:58:51 AM by cyber104 »
1978 TA 4-Speed W72

Wallington

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Re: Idle step up solenoid bracket for Q-Jet
« Reply #8 on: Today at 05:42:14 AM »
It won't have enough power to lift the throttle, only to maintain the set level when throttle is blipped.

cyber104

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Re: Idle step up solenoid bracket for Q-Jet
« Reply #9 on: Today at 06:01:27 AM »
Yes - agreed - thx for the confirmation
1978 TA 4-Speed W72

nUcLeArEnVoY

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Re: Idle step up solenoid bracket for Q-Jet
« Reply #10 on: Today at 08:30:28 PM »
It is true that these AC idle step-up solenoids don't have the ability to actually push the throttle lever under their own power (though interestingly, they can move it a fair bit if you disconnect the AC compressor so they they get more amperage). That is by their design, so that the car doesn't start moving at a stop light.

Even the service manual and your emissions decal states that you need to rev up the motor and lift the throttle lever to make sure the plunger is fully extended before you adjust it.

The whole idea is that once you turn on the AC, you blip the throttle so that the plunger fully extends and then holds the throttle lever at the higher speed. The tradeoff is, while you will have a stable, normal idle speed while the compressor is running (as is the purpose of the solenoid), when it is not engaged, you'll have to deal with a higher idle until you turn the AC off. The solenoid plunger doesn't extend and retract in conjunction with the AC compressor cycling on and off like it would in an ideal world; it instead stays energized until you shut off the AC.

Things like this really do make you have a newfound appreciation for an idle air control valve. It's why in the future when I get a stroker motor build, I'm converting to EFI. When you're a millennial like me, it's tough to adjust to seeing your idle drop 25 or so RPM just by turning on the headlights. Lol

1979 Trans Am 400/4-Speed W72/WS6 - Starlight Black Hardtop

Wallington

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Re: Idle step up solenoid bracket for Q-Jet
« Reply #11 on: Today at 09:31:01 PM »
That still happens with newer cars, unrelated to how the fuel system operates. Some may be more refined in their compensation of the new power use.

Re: Idle step up solenoid bracket for Q-Jet
« Reply #11 on: Today at 09:31:01 PM »
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