How Much Vacuum from Vacuum Check Valve
Thread Starter
Racer
Joined: Jan 2006
Posts: 323
Likes: 4
From: McKinney Texas
How Much Vacuum from Vacuum Check Valve
How much vacuum is your engine pulling at idle from the vacuum check valve?
I am diagnosing my vacuum system. 327/350hp, 750rpm idle. I get about 14 inches of vacuum at idle from the intake port, but only 5 inches of vacuum from the small port on the opposite side of the vacuum check valve. If I pinch the yellow line to the wiper door valve, the vacuum slowly moves up to around 10 inches. My headlights pop up when I do this as well.
It looks like the wiper door valve is leaking vacuum, but I was wondering what I am supposed to have.
I am diagnosing my vacuum system. 327/350hp, 750rpm idle. I get about 14 inches of vacuum at idle from the intake port, but only 5 inches of vacuum from the small port on the opposite side of the vacuum check valve. If I pinch the yellow line to the wiper door valve, the vacuum slowly moves up to around 10 inches. My headlights pop up when I do this as well.
It looks like the wiper door valve is leaking vacuum, but I was wondering what I am supposed to have.
Le Mans Master
Joined: Mar 2008
Posts: 5,948
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From: Oxford MA-----You just lost the game!!!!
If I understand you correctly, it should be the same as manifold vacuum. If you haven't already seen this thread, check it out, has alot of good info on troubleshooting the headlight vacuum system.
http://forums.corvetteforum.com/c3-t...tem-works.html
Scott
http://forums.corvetteforum.com/c3-t...tem-works.html
Scott
Race Director
Joined: Jul 2001
Posts: 15,892
Likes: 42
How much vacuum is your engine pulling at idle from the vacuum check valve?
I am diagnosing my vacuum system. 327/350hp, 750rpm idle. I get about 14 inches of vacuum at idle from the intake port, but only 5 inches of vacuum from the small port on the opposite side of the vacuum check valve. If I pinch the yellow line to the wiper door valve, the vacuum slowly moves up to around 10 inches. My headlights pop up when I do this as well.
It looks like the wiper door valve is leaking vacuum, but I was wondering what I am supposed to have.
I am diagnosing my vacuum system. 327/350hp, 750rpm idle. I get about 14 inches of vacuum at idle from the intake port, but only 5 inches of vacuum from the small port on the opposite side of the vacuum check valve. If I pinch the yellow line to the wiper door valve, the vacuum slowly moves up to around 10 inches. My headlights pop up when I do this as well.
It looks like the wiper door valve is leaking vacuum, but I was wondering what I am supposed to have.
Thread Starter
Racer
Joined: Jan 2006
Posts: 323
Likes: 4
From: McKinney Texas
No, it is correct, and new. I am just troubled by the drop from manifold level.
scottyp99, thank you for the thread, which I have been using. Like you, I thought it would be the same as manifold vacuum, but maybe the check valve was lowering it? There must be a leak in the wiper valve, and I suppose there could be one too in the headlight valve that is keeping it from equalling manifold vacuum.
imariver, thanks. Is that the same as your manifold vacuum?
scottyp99, thank you for the thread, which I have been using. Like you, I thought it would be the same as manifold vacuum, but maybe the check valve was lowering it? There must be a leak in the wiper valve, and I suppose there could be one too in the headlight valve that is keeping it from equalling manifold vacuum.
imariver, thanks. Is that the same as your manifold vacuum?
Thread Starter
Racer
Joined: Jan 2006
Posts: 323
Likes: 4
From: McKinney Texas
Race Director
Joined: Jul 2001
Posts: 15,892
Likes: 42
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Thread Starter
Racer
Joined: Jan 2006
Posts: 323
Likes: 4
From: McKinney Texas
It holds a vacuum (drawing on one of the two "in" pipes, plugging the other), no problem. Also drops my vacuum by about 4 inches, which apparently it is not supposed to do. Since it is new, I want to return it if there is a problem.
Race Director
Joined: Jul 2001
Posts: 15,892
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Again, the test you've performed indicating a 4" drop is not valid. What this reading means is there is a significant leak somewhere after the check valve that won't allow full vacuum to develop. Nothing wrong with the check valve, go after the downstream leaks.
