Ported vacuum switch ?

So did all cars come with a ported vacuum switch or just cars with a/c? If no PVS then would there be a plug of some sort on the water pump? Thanks

69/70 Bosses had them…no A/C there

My 429CJ Torino has one, no A/C.

Ok Cool. I guess that answers that! lol

Your copy of the factory shop manual tells if it did or didn’t. Nothing to do with A/C - not related in any way.

70 Shop Manual is written as if the “distributor vacuum control coolant temperature sensing valve” applies to all cars - at least for 1970.

The vacuum schematics are assigned by engine code and show exactly what you need to know.

Ford introduced the temperature controlled vacuum ported switch in the early to mid 60’s, it was primarily used to apply extra vacuum to the distributor when the car started to over heat, at the time it was only used for cars with A/C. Extra vacuum advanced the timing which cools down combustion temperatures, increases engine RPM, thus increases fan speed producing more air flow.

But in later years it was used to reduce emissions, depending on the application and where the car was sold. Some times it was used to retard timing to reduce emissions, other times not so.

I have one cougar (1970 Cleveland), it is setup to retard timing, It is a Californian car, it as A/C. The other cougar (1970 Cleveland) it is setup to advance timing if the engine starts to over heat, it does not have A/C.

As Royce has hinted at, you workshop manual is your best bet.

Peter :slight_smile:

At least for 1970, the shop manual will confirm that the temperature controlled ported vacuum switch was used for only one purpose. It switched distributor vacuum advance from normal ported carb vacuum over to manifold vacuum when the engine overheated. This was done to increase idle speed so the fan and water pump ran faster to increase cooling.

Some cars also had the dual advance distributors which applied manifold vacuum to distributor retard. This was done to retard timing at idle to more completely burn the fuel for emissions. This makes the engine run hotter. I don’t have all the specific vacuum routings for the different engines, but don’t believe the retard vacuum was ever routed through the temperature controlled ported vacuum switch.

You are %100 correct. But the difficulty is understanding how the dual vacuum advance works until you take one apart.

The retard side of the dual vacuum advance is not physically connected to the distributor point swivel plate (inside distributor) or the arm that is attached to the swivel plate. It does absolutely nothing if the advance side is receiving vacuum. All it does is move the rest position (inside the vacuum advance unit) of the vacuum advance side depending on the what condition the engine is in.

The higher the vacuum in the inlet manifold the more the retard rest position is moved towards the retarded side.

The amount of timing advance at idle is controlled by how much vacuum is supplied to the advance side of the vacuum advance unit, and this depends on if the vacuum is supplied from the intake manifold or the carburettor port.

(Note- The ported source at the carburettor, does not have any vacuum when the carburettor butterflies are closed.)

And whether the vacuum advance is supplied with vacuum from the carburettor port or the inlet manifold depends on the temperature controlled vacuum switch, which in turn depends on engine temperature.

So if the temperature controlled vacuum switch, switches vacuum supply to the carburettor port at idle, where there is no vacuum, the advance side will come to rest in the more retarded position.

Sorry, it’s not a very good explanation, very difficult to explain. I had to take a dual vacuum advance unit a part and then follow the vacuum diagrams before I could get it. Ask again if troubled.

Peter :slight_smile:

Indeed, very hard to put it all into words. But I do believe we are in agreement. And then further complicating things is the vacuum modulator that won’t pass carb (ported) vacuum to the distributor advance at low speeds - unless it’s cold outside.

I run with the distributor modulator disabled, and also blocked the vacuum line to the retard side of my dual vacuum advance. Engine and under hood temps run lower without it.

Probably the best thing to do is to simply see if it runs better with it hooked up and then without it.

If ermine temps and power are better with (or without) it hooked up, there’s your sign.

My 1968 has 2 vacuum ports on the distributor, one for manifold vacuum, one for ported. I have both hooked up & the vehicle runs fine.

I suspect that each vehicle might have its own quirks & testing on a case by case basis might be for the best.

After all, it’s all too easy to switch carbs and distributors that might be different then OEM. Maybe hooking up a timing light to see what is actually happening could also shed light on your situation.

Bottom line is that if it ain’t broke, don’t fix it.

Vacuum retard at idle shouldn’t affect driveability or power either way. I just prefer having my 351c run a bit cooler while idling on a summer day by not retarding timing at idle. Ford did it to more completely burn fuel at idle for emissions. But the exhaust manifolds on my car ran about 50 degrees hotter with timing retarded at idle. Heads ran more like 25 deg hotter.

Power is better in stop and go traffic without the vacuum modulator because it blocks vacuum advance at speeds under 20 mph. Ford was willing to sacrifice some performance here in order to meet emissions standards.

Agree on use of timing light. I had to replace my dual vacuum advance unit, so I checked both the centrifugal and vacuum advance curves to make sure they are in spec for my engine. The advance curve specs in the shop manual are given in terms of camshaft degrees, so you have to double them when measuring crankshaft degrees with a timing light.