OK Here’s A Question For Everyone

Engine, fuel system, cooling system, heating, carburetors, exhaust, transmission, wheels, and other items related to the moving the car.

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jon schapiro
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OK Here’s A Question For Everyone

Post by jon schapiro »

I unplugged the vacuum line to the vacuum motor on the air cleaner snorkel as it was keeping the flap closed hot or cold engine and I’m thinking the carburetor needs a better flow of air. I plugged the vacuum line temporarily. Shouldn’t the flap be open when the engine reaches operating temperature? I’m thinking the engine is air starved thus causing it to stall. Please advise if the flap should be open or closed at operational temperature.
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Re: OK Here’s A Question For Everyone

Post by action »

That valve is there to direct the correct air temp into the engine.
For start up and initial engine running the warm air is needed.
Once the engine coolant temp has come up some the warm air is no longer needed. Cold or cooler air is needed so the valve should change to air from outside of the engine compartment. Hence the big long hose leading to a plastic end that likely picks up air from outside of the engine compartment or at least close to the front of the vehicle.

In the early 1970s that door was controlled by heat sensitive wax in a small actuator connected to the door flap.
Later in the 1970s that arrangement was not as accurate as a vacuum operated door. The vacuum signal is controlled by a PVS valve. (Ported Vacuum Switch) There are 3 or 4 different PVS valve types and routings. I am assuming you are working on the 73 in your signature line. I think 1973 pre-dates an engine vacuum routing sticker. And the routing should be found in the shop manual. However it is hard to find at least in the 1970 & 1971 shop manuals that I have. By 1973 the company may have gotten better.

If the door is always open or always closed, yes there is an issue. Either the door is stuck, there is a vacuum leak or the signal switch is not functioning.
Sounds like the door functions. Check for leaks in the hose and door motor.
The PVS should be screwed into the intake somewhere in front or sometimes behind the carb. It is another waxed based vacuum switch that changes positions based on heat. The PVS valves are usually color coded. Most of the time the colors are long gone at this point on uses switches. The colors usually stand for the circuit type or for the temp the valve switched.

Here is an article on the 3 ported switch for the distributor
https://www.428cobrajet.org/id-dist-vac-valve

PVS control vales come in 2, 3 and 4 port varieties. In addition some vacuum circuits had delay valves inline with the circuit to slow down the switching. Some valves handled more than one circuit. A lot of engineering went into the use of engine vacuum circuits to accomplish a lot of different things.

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Last edited by action on Thu Jun 17, 2021 3:47 pm, edited 2 times in total.
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1970 Continental Mark III Triple Black 460 4v, C6, 2.80 (Used for Woodward Dream Cruise or just generally stored in Michigan)
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1966 Mercury Park Lane 4DR Breezeway 410 4v, C6, 2.80
jon schapiro
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Re: OK Here’s A Question For Everyone

Post by jon schapiro »

Understood and totally agree so I am thinking my engine was air starved once warm and that was causing my stalling problem. Tomorrow I will check it out for a run and see if that pans out
Last edited by jon schapiro on Thu Jun 17, 2021 3:56 pm, edited 1 time in total.
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TonyC
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Re: OK Here’s A Question For Everyone

Post by TonyC »

Just to supplement Action's input, if my research is correct, the flap is closed off to outside air when the engine is cold, so only air heated through the exhaust manifold enters the carburetor. As the engine warms up, a thermostatic control sensor inside the air cleaner manipulates manifold vacuum and opens the flap to outside air which is warmed up by built-up heat in the engine bay (from what I've read, that sensor applies vacuum to the servo when the engine is cold, closing the flap, and cuts off vacuum from the servo as the engine warms up, opening the flap). If you suspect a fault, you can test the flap control servo with a vacuum pump. If vacuum holds, the thermostatic control may be faulty; that can be checked by placing an ice cube on the sensor and checking operation with the engine running (the ice cube keeps the sensor in its cold-engine setting while the engine is running). If you don't feel vacuum at the end of the hose that connects to the servo, then the heat sensor needs replacement. If you do feel vacuum and you've also confirmed that the servo in the snorkel and the flap hatch work as they should, then the system is fine and not the cause of your problem.

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Re: OK Here’s A Question For Everyone

Post by jon schapiro »

Tony - I am getting vacuum to that little vacuum motor all the time hot or cold so I’m thinking the three-way vacuum sensor may be defective but for a quick test I will just disconnect the vacuum hose and plug it as the spring inside the snorkel opens up the flap and see how the car runs that way. I will post again once I test drive it tomorrow
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Re: OK Here’s A Question For Everyone

Post by action »

TonyC wrote: As the engine warms up, a thermostatic control sensor inside the air cleaner manipulates manifold vacuum and opens the flap to outside air which is warmed up by built-up heat in the engine bay

---Tony
That is another variation of air door control.
The thermal sensor is in the air cleaner and did not use a PVS for switching. Some of those buzz rather loudly when they reach the switch temperature

Action
Phoenix - Yeah, it's hot, however it's a dry heat
2006 Lincoln Navigator Limited 5.4l 3V
1996 Lincoln Mark VIII 2DR Coupe Diamond Anniversary 4.6l DOHC, 4R70W, 3.07
1970 Continental Mark III Triple Black 460 4v, C6, 2.80 (Used for Woodward Dream Cruise or just generally stored in Michigan)
1966 Lincoln Continental 4DR Convertible 462 4v, C6, 3.00
1966 Mercury Park Lane 4DR Breezeway 410 4v, C6, 2.80
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Re: OK Here’s A Question For Everyone

Post by jon schapiro »

Well I don’t want to jinx it but I took the car on the same run as the other day and it seemed to run perfectly. I then went a bit further. When I got back to the garage I let it idle for a few minutes and it sounded nice and smooth. I have to admit I still have this nervous feeling while driving it as there is nothing worse than a car stalling and knowing there are no mechanics out there who know 1/4 of what I know. As expected, I did not feel anything different when driving it ice cold as cars prior to this never had that carburetor air preheater concept. I think I will take it out each day and drive a bit further each time until my confidence in the car builds up.
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Re: OK Here’s A Question For Everyone

Post by TonyC »

Well, they did, but the design of the preheating apparatus on pre-'70s cars was different, simpler (some would possibly say "cruder"). It may be a wonky sensor switch causing the sporadic issue; it's just a matter of identifying and locating that switch.

---Tony
"Don't believe everything you read on the Internet, just because there is a picture with a quote next to it." (Abraham Lincoln, 1866)
"Question Authority!"

1966 Continental Sedan, affectionately known as "Frankenstein" until body restoration is done (to be renamed "General Sherman" on that event)
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Re: OK Here’s A Question For Everyone

Post by George W »

I would assume that it's unlikely that you'll be using the car in freezing weather so if you have to you could secure the flap to the open position permanently. Make sure though if you have an open vacuum line that you cap it off.
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