Vacuum advance TVS question?

[Silver State 77]

Im connecting vacuum hoses on a 1977 6.6 and im seeing the strangest thing, it looks like the vacuum advance is getting ported vacuum until the engine warms up, and then it gets manifold vacuum. is that right?
Why would they attach the manifold vacuum line to that Thermal switch?
Is that why they want the timing set so far advanced at 20 deg.?

 

[melsg5]

Im connecting vacuum hoses on a 1977 6.6 and im seeing the strangest thing, it looks like the vacuum advance is getting ported vacuum until the engine warms up, and then it gets manifold vacuum. is that right?
Why would they attach the manifold vacuum line to that Thermal switch?
Is that why they want the timing set so far advanced at 20 deg.?

Looking at the diagram there is only one source of vacuum coming from the carburetor and it is used for both the distributor and EGR valve once the TVS opens.

 

[cammerjeff]

I agree that there is only 1 source of vacuum for the Distributor on that diagram. As to why they would do it that way, they had to meet cold start emissions using the technology they had at that time. The limit the vacuum advance until the engine comes up to operating temperature. And remember the different divisions engines all had slightly different emissions controls. I am assuming you have a 403 Olds engine in your 77 GP, and not the 400 Pontiac version.

If you really are interested in how the system was supposed to operate get a copy of the 1977 GM emissions manual like the one on this link

VINTAGE 1977 GM TRAINING EMISSION CONTROL SYSTEMS MAINTENANCE MANUAL GUIDE BOOK | eBay

We're passionate about uncovering and restoring the stories of the treasures from your grandparents and great grandparents history. We believe in breathing new life into the world's first modes of transportation.

www.ebay.com

 

[Silver State 77]

Looking at the diagram there is only one source of vacuum coming from the carburetor and it is used for both the distributor and EGR valve once the TVS opens.

Here is a better picture showing the 3rd vacuum line going under the PCV hose, it is connected to Manifold Vacuum.
The sticker under the hood shows the same thing, but my question is, How can your vacuum advance work in reverse, once the TVC opens?

______________________________

 

[Silver State 77]

I agree that there is only 1 source of vacuum for the Distributor on that diagram. As to why they would do it that way, they had to meet cold start emissions using the technology they had at that time. The limit the vacuum advance until the engine comes up to operating temperature. And remember the different divisions engines all had slightly different emissions controls. I am assuming you have a 403 Olds engine in your 77 GP, and not the 400 Pontiac version.

If you really are interested in how the system was supposed to operate get a copy of the 1977 GM emissions manual like the one on this link

VINTAGE 1977 GM TRAINING EMISSION CONTROL SYSTEMS MAINTENANCE MANUAL GUIDE BOOK | eBay

We're passionate about uncovering and restoring the stories of the treasures from your grandparents and great grandparents history. We believe in breathing new life into the world's first modes of transportation.

www.ebay.com

I have a Pontiac 403 engine in my 77 Grand Prix, same as a Trans Am. It was first sold new in Utah, so it does not have a smog pump or cat converter.
Its shaking at all RPMs at first I thought it might be the carburetor, but now im thinking its an ignition problem.
That is what i get for changing too many parts at the same time. Now I have to put old stuff back on to see if it runs better. Lol;

 

[Silver State 77]

Hey Jeff, Check out my picture of my Grand Prix when I first saw it for sale, kind of spooky.

 

[melsg5]

Here is a better picture showing the 3rd vacuum line going under the PCV hose, it is connected to Manifold Vacuum.
The sticker under the hood shows the same thing, but my question is, How can your vacuum advance work in reverse, once the TVC opens?

Sorry dont see how that second diagram is showing any other vacuum source to the distributor. You have one hose connected to distributor going to the TVS valve. How many ports does your TVS have?

 

[Silver State 77]

Sorry dont see how that second diagram is showing any other vacuum source to the distributor. You have one hose connected to distributor going to the TVS valve. How many ports does your TVS have?

Sorry, Its not a solid fat line, like the other ported vacuum lines are shown,
I used my paint, to color the 3rd line in Green, and left the original document lines to show its validity.

______________________________

 

[Silver State 77]

Its a mystery why they think all the smog devices installed on engines to burn cleaner, when all they really seem to do is, make it cost more money, use up more gas, and eventually destroy an engine with its own exhaust and back pressure.
I believe, these older classic cars that are still running today, its because they were made in the days before smog device.
I have a 1974 el Camino that my dad gave to me over 23 years ago, and it has over 500000 miles on the original engine, its very reliable transportation, with great gas millage, and its smog exempt. THANKS dad

 

[melsg5]

Sorry, Its not a solid fat line, like the other ported vacuum lines are shown,
I used my paint, to color the 3rd line in Green, and left the original document lines to show its validity.

How many ports on the TVS?
Are these lines missing currently that you need to refer to a diagram?

 

[cammerjeff]

Yeah White 70's Pontiac's on a trailer! Kinda spooky, I just managed to get that Catalina moving again under its own power last month. It runs strong for a 50+ year old car.

 

[Silver State 77]

How many ports on the TVS?
Are these lines missing currently that you need to refer to a diagram?

Yes, there is a sticker under the hood that shows the vacuum lines and the things they are connected to, and the smog guy will look at it and then he will look at my new carburetor and check to see if everything is like the sticker, and if its not the same as the sticker under the hood, the car will not pass smog.

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[Silver State 77]

I just got back from a test drive, and it drives nice and smooth, and I can feel that Pontiac 403 power. the brakes work good, next is the smog check, This car is giving me teen age memories of when i worked on my 1955 Oldsmobile, I paid $100 for. Back in those days they were glad to get rid of it, and lucky to find anyone willing to buy a car that did not drive.

 

[Silver State 77]

Yeah White 70's Pontiac's on a trailer! Kinda spooky, I just managed to get that Catalina moving again under its own power last month. It runs strong for a 50+ year old car.

You know My Grand Prix has that same rust coming through the paint. So did my El Camino, and eventually the hood and top were nothing but rust. so the time to paint is before the paint is gone, or we will be sanding all night long.

 

[Silver State 77]

So yesterday a got the smog check done, and the guy told me Someone removed the cat converter. I asked how do you know if it had one? he said its on the sticker. I saw the sticker and it says, CATALYST EGR That is all it says.
That is only a sticker, is there a way to look up our VIN and confirm what the sticker says, because I dont believe the previous owner would remove the converter, they had the car since 1986, they lived in the mountains of Utah where they salt the roads for traction, and it could have rusted out the tail pipe, and when he had the exhaust pipe replaced, they did not bother replacing the converter?
I dont know, but my El Camino sticker gives 2 engine sizes and also mentions Removing the gas cap on "Corv. models"
So it shows the same stickers were used on many cars back then.
So the Smog guy failed me on the Smog check, But, I got this car running good now, I hauls butt, and I can feel that 403 power, And you guys helped me do it. Thanks again

 

[cammerjeff]

Almost all cars sold by GM starting in 1974 used Cat Converters, there are a couple of exceptions, but your car defiantly came from the factory with a Cat converter. Some previous owner removed it for some reason before you purchased it. Either it had rusted out, or was clogged. The pellet type converters used at the time were very prone to clogging when they reached about 79-80k miles.

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[melsg5]

So yesterday a got the smog check done, and the guy told me Someone removed the cat converter. I asked how do you know if it had one? he said its on the sticker. I saw the sticker and it says, CATALYST EGR That is all it says.
That is only a sticker, is there a way to look up our VIN and confirm what the sticker says, because I dont believe the previous owner would remove the converter, they had the car since 1986, they lived in the mountains of Utah where they salt the roads for traction, and it could have rusted out the tail pipe, and when he had the exhaust pipe replaced, they did not bother replacing the converter?
I dont know, but my El Camino sticker gives 2 engine sizes and also mentions Removing the gas cap on "Corv. models"
So it shows the same stickers were used on many cars back then.
So the Smog guy failed me on the Smog check, But, I got this car running good now, I hauls butt, and I can feel that 403 power, And you guys helped me do it. Thanks again

Your car definitely came with a catalytic converter in 77.

 

[Silver State 77]

These are the latest pictures showing what a can of paint and a good bath can do.

 

[Silver State 77]

Your car definitely came with a catalytic converter in 77.

Right, I guess i was believing an old rumor, in the seventies they said, if you go outside of california, you can buy any new car without smog device, thinking smog device was just a california thing. but it was a federal thing. 3 things, a cat converter, an EGR valve, and the air cleaner heat stove on the exhaust manifold.
I did take a look at the pipe, and I can see where someone joined the muffler to the same size pipe, using a 3/4 inch long piece of bigger pipe, welded around the two, and the pipe between the manifold and muffler was remade without the converter, a very long time ago.