EGR Valve
Melting Slicks
Joined: May 2006
Posts: 3,438
Likes: 41
From: Raleigh NC
St. Jude Donor '13-'14
Burning Brakes
Joined: Apr 2013
Posts: 926
Likes: 2
From: Castle Rock CO
It is a required component on the Emission Control system but can be removed on modified engines where the Emission controls are not necessary. Best to replace it if you think it is bad if you live somewhere emissions are inspected on pre 1980 cars.
The EGR (exhaust gas recirculation) valve recirculates exhaust gases through the intake manifold to be burned again, cooling peak combustion temperature. Dilutes the air and fuel mixture to keep the nitrogen oxide emissions within breathable limits
The EGR (exhaust gas recirculation) valve recirculates exhaust gases through the intake manifold to be burned again, cooling peak combustion temperature. Dilutes the air and fuel mixture to keep the nitrogen oxide emissions within breathable limits
Last edited by MakoJoe; Oct 30, 2013 at 10:28 PM.
Burning Brakes
Joined: Apr 2013
Posts: 926
Likes: 2
From: Castle Rock CO
If my 1977 was not parked for the winter, covered up and in storage away from home in another garage I would take a picture for you but it is in storage for the next 6 months for winter.
Pro
Joined: Oct 2013
Posts: 627
Likes: 119
From: Denver CO
It would be a part-throttle vacuum source higher up on the carb. You want it above the level of the vacuum advance on the distributor. Some are linked through a temp control valve (in the manifold coolant passage) to inhibit it's operation until the engine has warmed up.
Thread Starter
Racer
Joined: Jul 2013
Posts: 423
Likes: 6
Thanks for that information, Is there a way to test them to be sure they are working or would it be best to replace it ?
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Pro
Joined: Oct 2013
Posts: 627
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From: Denver CO
A Mitivac to the diaphram to see if it's lifting the cork and holding vacuum. You can clean the lower part if you hold the cork open and scrape out all the carbon from the seat area and the passage above.
The manifold valve is just to test if you have no flow when it's cold and flow when it's warmed up. Like a thermostat.
Note: a Smog Tech cannot fix, but must replace by law.
The manifold valve is just to test if you have no flow when it's cold and flow when it's warmed up. Like a thermostat.
Note: a Smog Tech cannot fix, but must replace by law.
Last edited by MSGT-R; Oct 31, 2013 at 12:07 PM.
Thread Starter
Racer
Joined: Jul 2013
Posts: 423
Likes: 6
A Mitivac to the diaphram to see if it's lifting the cork and holding vacuum. You can clean the lower part if you hold the cork open and scrape out all the carbon from the seat area and the passage above.
The manifold valve is just to test if you have no flow when it's cold and flow when it's warmed up. Like a thermostat.
Note: a Smog Tech cannot fix, but must replace by law.
The manifold valve is just to test if you have no flow when it's cold and flow when it's warmed up. Like a thermostat.
Note: a Smog Tech cannot fix, but must replace by law.
2026 Loser of the Year
Joined: Sep 2013
Posts: 36,607
Likes: 7,053
From: New Or-leens Loo-z-anna
I'm a rookie....but from what the posts say, you can route the vacuum line straight from the EGR nipple to a carb nipple that does NOT have a constant vacuum, but has a vacuum that varies with engine rpm.
It sounds like the cold engine may idle a little rough until it reaches operating temperature without having the bypass (solenoid switch/temp switch/whatever) connected between the EGR & the carb.
But-------Like another member said...OEM diagrams show the factory routing in case you're going for original usage.
It sounds like the cold engine may idle a little rough until it reaches operating temperature without having the bypass (solenoid switch/temp switch/whatever) connected between the EGR & the carb.
But-------Like another member said...OEM diagrams show the factory routing in case you're going for original usage.
Thread Starter
Racer
Joined: Jul 2013
Posts: 423
Likes: 6
I'm a rookie....but from what the posts say, you can route the vacuum line straight from the EGR nipple to a carb nipple that does NOT have a constant vacuum, but has a vacuum that varies with engine rpm.
It sounds like the cold engine may idle a little rough until it reaches operating temperature without having the bypass (solenoid switch/temp switch/whatever) connected between the EGR & the carb.
But-------Like another member said...OEM diagrams show the factory routing in case you're going for original usage.
It sounds like the cold engine may idle a little rough until it reaches operating temperature without having the bypass (solenoid switch/temp switch/whatever) connected between the EGR & the carb.
But-------Like another member said...OEM diagrams show the factory routing in case you're going for original usage.
Melting Slicks
Joined: May 2006
Posts: 3,438
Likes: 41
From: Raleigh NC
St. Jude Donor '13-'14
Spend $30 more and get the proper EGR Thermal switch. From memory, it should thread into the thermostat housing, but maybe it is in a different location for a 1978 corvette.
Pro
Joined: Oct 2013
Posts: 627
Likes: 119
From: Denver CO
Just disconnect it until you can get another thermal valve (plug the vacuum source too). Running it cold could cause rough-running, and serves no purpose until you can get it fixed. If you have a visual smog check, they will check for both form and function. Just get it fixed before then.
Later vintage cars use an EGR sensor that checks for operation, and will trigger a check engine light if it doesn't sense movement when it's supposed to be open.
Later vintage cars use an EGR sensor that checks for operation, and will trigger a check engine light if it doesn't sense movement when it's supposed to be open.
Thread Starter
Racer
Joined: Jul 2013
Posts: 423
Likes: 6
Just disconnect it until you can get another thermal valve (plug the vacuum source too). Running it cold could cause rough-running, and serves no purpose until you can get it fixed. If you have a visual smog check, they will check for both form and function. Just get it fixed before then.
Later vintage cars use an EGR sensor that checks for operation, and will trigger a check engine light if it doesn't sense movement when it's supposed to be open.
Later vintage cars use an EGR sensor that checks for operation, and will trigger a check engine light if it doesn't sense movement when it's supposed to be open.
Team Owner
Joined: Aug 1999
Posts: 30,995
Likes: 99
From: Ontario
Get a thermal vacuum switch (TVS). NAPA will have it. You don't want EGR function at low engine temps (hence the TVS) and you don't want it with manifold vacuum (hence a ported source on the carb).
Thread Starter
Racer
Joined: Jul 2013
Posts: 423
Likes: 6
Team Owner
Joined: Aug 1999
Posts: 30,995
Likes: 99
From: Ontario
I can't give you the "right" answer for a 1978 as I drive a 1974. But this pic shows the TVS connection to the EGR and to ported vacuum above the throttle plate. So what you are looking at is temperature control of the EGR when engine is cold and throttle/vacuum control when the engine is at operating temperature. Sorry I cannot be of great help.
BTW, that is a very old pic and the valve covers were on the wrong side.
BTW, that is a very old pic and the valve covers were on the wrong side.
Thread Starter
Racer
Joined: Jul 2013
Posts: 423
Likes: 6
I can't give you the "right" answer for a 1978 as I drive a 1974. But this pic shows the TVS connection to the EGR and to ported vacuum above the throttle plate. So what you are looking at is temperature control of the EGR when engine is cold and throttle/vacuum control when the engine is at operating temperature. Sorry I cannot be of great help.
BTW, that is a very old pic and the valve covers were on the wrong side.
BTW, that is a very old pic and the valve covers were on the wrong side.
Melting Slicks
Joined: May 2006
Posts: 3,438
Likes: 41
From: Raleigh NC
St. Jude Donor '13-'14
Right! So for 1978, the TVS on the thermostat housing is for the EFE actuator that is connected to your passenger side manifold. Your EGR TVS is mounted in a port on the manifold (which you've shown above).
I'm guessing you have an L-48? Check out Doc Rebuild's page, you can zoom in on his kit and see the correct ports for a quadrajet.
http://shop.docrebuild.com/1978Corve...eplacesGM.aspx
I'm guessing you have an L-48? Check out Doc Rebuild's page, you can zoom in on his kit and see the correct ports for a quadrajet.
http://shop.docrebuild.com/1978Corve...eplacesGM.aspx