I'm getting close to completing the vacuum line replacement and factory-correct installation on my 1979 Catalina, and I'm just a bit stumped by a couple of things. I attached the official GM vacuum diagram from the service manual that matches my car. This diagram is a little bit unclear with the EFE & EGR-TVV part to the far left. It took me a couple days to figure out that this thing is broken into two parts, not a single fitting. One is a pair of barbs hiding underneath the air box, with a part protruding inside, and the other thing has a pair of barbs on top of the block. There's also a single barb that's not connected to anything also attached to the bottom of the air box. I assume the single barb that is by itself was meant for the check valve? Before taking the line off, I noticed it was open to the atmosphere. There was no vacuum mechanism present, thus it was probably causing a vacuum leak.
I'm a bit confused on manifold vacuum vs ported vacuum, and how to tell the difference in the two when you pull a vacuum line off. I'm not positive I have the manifold line and ported line set up correctly on the two devices. There's a very large valve in the intake of the airbox labeled Thermac, with one vacuum barb, is that the same as the EFE valve? In my current configuration, the valve is open when the engine is hot. At the moment, I have one port on the carb that is not in use, and I'm not sure which it is.
Not gonna answer here, but impressed and inspired of your work! Keep it up! Hopefully you get it soon!
I watched a non-Scotty video on my lunch break at work that explained the various vacuum ports on a Rochester Quadrajet carburetor. Mine is a Rochester Dual-jet, but they're similar enough that you can cross reference them for most of the lines. It expanded on manifold vs port vacuum and what usually goes on each kind. Armed with that info, after I got home from work I went out and took one last look under the hood with a flashlight. I got it pretty much figured out after re-examining the under-hood diagram. The EFE valve line will go to the switch I was talking about earlier, and that has a single line to a manifold port. One of my new lines from the other day is slightly wrong, it needs to connect to this line with a T as well. I'll be able to fix in the morning. The line to the EFE valve was directly connected to the carb before I touched it, which was incorrect.
The EGR valve does not connect to that vacuum switch on my particular car, per the car's diagram. It connects directly to another manifold vacuum barb on the carburetor, which is interesting. The Auto Thermac system also connects to a manifold line, and was incorrectly connected originally.
Manifold vacuum is when the throttle plate is almost closed. It is BELOW the throttle plate. Port vacuum is ABOVE the throttle plate and increases when you open the throttle. Which is why the distributor operate off Port vacuum and advances as you accelerate and the throttle plate is open. Before pulling vacuum lines off, you're supposed to label them and where they go to. Since you have the diagram, just hook everything up per the diagram.
This car had pretty much no vacuum lines in their correct locations, so I'm trying to get them all the correct way again, lol. I've got the whole top half of this diagram back in order.
Just take your time, you'll get it have have the satisfaction of knowing it's right.
The problem with disabling temperature control of the EGR valve is that it can cause problems when the engine is cold. Usually EGR is prevented from operating until the engine reaches operating temperature. Likewise other temperature controlled vacuum valves determine when vacuum is allowed to the distributor advance.
The trouble with a car from that old is that the vacuum operated emission control systems are complex and by this time typically have been butchered badly. Some parts may no longer be available.
Since you don't need to worry about emissions testing ultimately what you could do is look at ditching most of that stuff and setting up the engine as much as possible the way it would have been a decade prior. I figured it would be best to set it to factory specs first but if parts are not available that might not be possible.
I'm honestly not sure a single one of te vacuum hoses was in the proper place, it was so butchered up and bypassed. I might try the tree idea on the TVV assembly I have and see what that does, if I can even find that check valve.
You wouldn't happen to know if the Thermac system in the air cleaner is supposed to be port or manifold powered, would you? That's the system that operates the large valve in the inlet to the air cleaner.
Probably manifold vacuum since it's controlled thermally rather than by the amount of vacuum.
Ultimately you would want the distributor vacuum advance to be hooked up to ported vacuum. If you look at the diagram, the factory setup is to use manifold vacuum routed through a bunch of emission control gadgets to regulate spark advance which may not always agree with the engine's need at the time. That kind of thing is one of the reasons why 1970s cars had poor performance and gas mileage.
I think I figured out what my problem is. The EFE and EGR thermo vacuum valve that's currently in the car only has two hose barbs, not 4 as the diagram calls for. The Thermac system in the air cleaner is a separate thing I'll need to straighten out later.
I looked around on Google and can't seem to find another 4-barb TVV, only 3-barb models, so I have a couple of ideas to fix this:
1. The EGR valve requires manifold vacuum, so I could splice in a line T off the manifold line going back toward vacuum advance and run the splice to the EGR valve. That would keep the EGR valve at a constant vacuum, not temp controlled. Would there be any possible negative effects from doing this? I could then use the 2-barb TVV I have now to actuate the emissions check valve and EFE valve.
2. Keep the same approach, only splice a port vacuum line so it will constantly put vacuum to the EFE valve and that check valve, so the EGR valve gets the controlled vacuum.
3. I'm not sure how these TVVs work, but if they apply and cut vacuum to the attached lines simultaneously, I could Frankenstein some hose T's together and get 4 to come off the two on the TVV, then hook everything up to that the way the diagram shows.
Do any of these sound like they would work out better than the others?
I know this is a weird idea, but given your situation, it might be a good idea to switch over to an aftermarket fuel injection system that would not only make the engine run better, but would be able to pass smog requirements. Just a thought. All those thermal vacuum switches just aren't available anymore.
Luckily I live in Ohio, and nobody cares about vehicle emissions here, so I can run a carburetor that wouldn't pass e-check anywhere else, haha.