Headers for economy on 82 K10?

[SirRobyn0]

By ported vacuum you mean timed vacuum and not manifold vacuum correct? Time permitting I will get the Mytivac out and see if the valve is working. My heat riser is connected, not sure if the flapperdoodle (thermac?) is functioning properly. How can I test that? Just observe? I do know that it starts right up on the first turn of the key even in single digits and runs very well under all conditions even if it is down on power compared to older V8s I have owned. My 20+ years working on old Porsches didn't prep me for troubleshooting GM emissions systems. Could you possibly give me a basic idea of how the EGR system works? I appreciate your help.

Sure.

So there are three separate but also working together systems we are talking about. The EGR system, Heat riser and Thermac.

I'm going to start with the heat riser. So the heat riser is the valve in the passenger side exhaust manifold just before the down pipe. Traditionally the heat riser is controlled by a bi-metalic spring on the exhaust manifold which as it heated opened the heat riser valve, later on the heat riser became vacuum controlled, so it would stay closed longer, and be regulated by engine temp, not exhaust temp. There is a passage in each cylinder head, and in the intake manifold called the exhaust cross over, when the heat riser is shut hot exhaust is routed though that passage and most of the exhaust ends up leaving though the drivers side manifold. The purpose is heat the bottom of the intake manifold when the engine is cold to improve fuel vaporization.

So the EGR draws exhaust gas out of this same port in the manifold, but when the EGR is open it sends a small amount of exhaust gas though ports in the manifold where it goes into the combustion chamber. To answer your question about ported vacuum, depending on the carb manufacture and whos talking, timed vacuum is either a special port for distributor vacuum or it's the same thing as ported. But it doesn't really matter for the sake of our discussion it's the same thing and it's fine to hook the EGR to ported or timed vacuum.

Thermac. This is on the factory air cleaner right on the snorkel. Manifold vacuum is connected to a temperature regulating sensor on the air filter housing, generally it's just called an air temperature sensor. There is a flexible black tube that runs to the air intake by the radiator to draw cool fresh air, and a smaller silver tube that connects to a shield on the exhaust manifold, to draw warmed up air from around the outside of the exhaust manifold. There is a flapper in the snorkel and this is the actual thermac. The thermac is fed a varying amount of vacuum by the by the air temp sensor to create an approximant incoming air temperature of 90F.

Hopefully that all makes sence, feel free to ask questions.

 

[t44e6]

SirRobyn0 I hooked a Mityvac up to the EGR valve at the exhaust manifold and with engine (warm) running actuated the valve. No difference in operation of the engine, the valve itself did actuate. The vac hose that goes to the control for the flapper in the snorkel is not connected, it is just hanging loose. There is a vacuum port in the manifold behind the carb (Q-Jet) that is plugged. No idea what goes there. With the thermoswitch on the T'stat housing disconnected there is a lot of plumbing that isn't right. There is a component on the side of the carb behind the choke that looks like it has an open port, anti dieseling solenoid? I think on some earlier GM cars they were electric. The Evap canister is hooked up except for the hose that is for the EGR. The engine runs great, and is burning with a good mixture. Plugs are a nice tan and burning clean. If I get bored enough I may try and figure it all out.​