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Throttle Position Solenoid Question
#1
‘72 Mach1 w/351C, Toploader, factory A/C, and original Autolite 4300 4 barrel.

Needed a new heater core, so I had a shop that specializes in vintage A/C update it as well with new heater box, new evap and whatever the new refrigerant is called.

Everything works fine, except that the throttle position solenoid kicks in at startup, and stays up even when the A/C is off. The shop says that it is wired per the original Ford wiring diagrams, and when I checked, it looks like that is true.

When this car was new (yes, I’ve owned it that long), the solenoid would only kick in when the  A/C was turned on. It would hit a small flat section on the throttle arm and increase the idle speed by a few hundred rpm, so the engine wouldn’t stall due to the added load of the compressor.

QUESTION-Does anyone know what the wiring should be for the solenoid? I’m thinking it should be linked to the A/C clutch wire. This car was built in April ‘72, which was after the major factory engineering changes of December ‘71, so maybe there was never a final factory wiring diagram for cars built between Jan ‘72 and the ‘73 model changeover. (I was working for Ford back then, and it would not surprise me if it were true)
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#2
My 73 with 351C and 2bbl carb and AC had one of these as well. It was on when the ignition was on and was not AC dependent. Everything under the hood was bone stock original and untouched as the car only had 67,000 miles on it when I purchased it. I do not know if the solenoid served a different function in 72 vs 73 or 2 bbl vs 4 bbl though. It was my understanding that it's function was an anti-diesel device that would allow the butterflies to close completely when the car was shut off.

'73 Grandé H Code. Headman long tube headers, T-5 Transmission, 3.70 Traclok, Lowered 1" all around, Aussie 2v heads w/ 2.19 intake, 1.71 exhaust, screw in studs, full roller cam 608/612 lift 280/281 duration LSA 112, Quick Fuel 750 CFM double pumper, AirGap intake.

'73 F code convertible. Bright red. Needs total restore. (IE HOT MESS)

- Jason
[+] 1 user Likes 73pony's post
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#3
Jason's answer is consistent with the wiring diagrams for both '72 and '73. Neither show a connection between the AC circuit and throttle position solenoid. You can download the circuit diagrams under the Mustang Data tab at the top of the page.



“If you can't explain it simply, you don't understand it well enough.”
--Albert Einstein
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#4
(11-07-2018, 05:57 PM)Don C Wrote: Jason's answer is consistent with the wiring diagrams for both '72 and '73. Neither show a connection between the AC circuit and throttle position solenoid. You can download the circuit diagrams under the Mustang Data tab at the top of the page.

Thanks for the info guys.
This may explain an issue that I had with the car when I first got it from the dealer in ‘72, and it was set up wrong ever since.
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#5
As mention. It's just only to stop the chug-a chug after ignition is shut off. As for the A/C, it can't push open the throttle ( if wired) to compensate the idle rpm drop. It can only hold it with some help.
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#6
Agreed, it's the ainti-dieseling solenoid. When the ignition is turned off, it snaps the throttle blades shut completely. The "idle screw" on the carburetor should be adjusted to allow complete closure or just a few thousandths of opening, check the shop manual. Your actual idle speed is set with the adjuster on the solenoid bracket.


[+] 2 users Like Hemikiller's post
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#7
(11-08-2018, 09:01 AM)Hemikiller Wrote: Agreed, it's the ainti-dieseling solenoid. When the ignition is turned off, it snaps the throttle blades shut completely. The "idle screw" on the carburetor should be adjusted to allow complete closure or just a few thousandths of opening, check the shop manual. Your actual idle speed is set with the adjuster on the solenoid bracket.

Got it! 
Thanks to all.
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#8
I have problems with that very thing on mine. I just unplugged it and reset the idle. I don't have any dieseling issues.
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