Most likely cause.
Vacum problem
Thread Starter
Pro
Joined: Jun 2005
Posts: 592
Likes: 1
From: Georgetown IN
Vacum problem
Working on a 70 350/350 car for a friend. At idle the wiper door and both headlight doors want to pop up. As soon as you rev it they will start to close and driving down the road they will remain closed. As any one fooled with this problem? Any ideas?
Thanks
Thanks
Safety Car
Joined: Feb 2006
Posts: 3,557
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From: Ridgeway VA
Had the same thing happen with my '70 at startup. In my case it was a simple matter of making sure all hose connections are firmly on. Check hose on manifold, and make sure the rubber plug on the front of the wiper canister is firmly on - if not get a new one. The, the list goes on ...
Team Owner
Joined: Sep 2006
Posts: 31,172
Likes: 4,250
From: Westminster Maryland
Hi H,
My thought is that there's a slow leak in the control side of the system. At idle the vacuum isn't high enough to keep up with the leak, at high RPM's it is. A check valve leak as Mike suggests, a hose leak as PK suggests, or maybe a relay leak?
Regards,
Alan
My thought is that there's a slow leak in the control side of the system. At idle the vacuum isn't high enough to keep up with the leak, at high RPM's it is. A check valve leak as Mike suggests, a hose leak as PK suggests, or maybe a relay leak?
Regards,
Alan
Race Director
Joined: May 2006
Posts: 16,528
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From: Dayton, Ohio
Try bringing the rpms up slowly until the lights and wiper doors close down and hold that rpm,with a pair of pliers pinch off the hose between the manifold and 3 port metal check valve and watch what the lights do.If they stay down,replace the 3 port valve.My guess is they will come up and you have a leak in the small hose side of the vacuum system.
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Race Director
Joined: May 2006
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From: Dayton, Ohio
Why? The engine idles at almost full vacuum,why would the checking action of the valve fix this?It almost has to have a leak that the engine needs to keep up with in the control side (small hose).Doing my pinch test will act like a new check valve was installed and will most likely show that the valve is not the problem.
Team Owner
Joined: Jan 2006
Posts: 37,637
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From: Crossville TN
Sounds like you want the 'logical' reason for a bad check valve acting the way it does. Well, I can't provide that...but that's what happens. Take your "good" check valve out of the system and see what happens.
Race Director
Joined: May 2006
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From: Dayton, Ohio
No reason to take anything out....just pinch the hose and instantly you have a check valve...if the lights still come up then the check valve is not the reason.
edit-I'm not saying the check valve is not bad only that I dont believe thats the reason for the headlights to pop up.The only time you really need the check valve is when the vacuum is low due to wide open throttle or you shut the engine off and you want the lights to come up.
Hurri whether you replace the valve or not make sure you replace the little white filter thats in between the valve and the manifold.This filter protects the 3 port metal check valve from engine contaminants.
edit-I'm not saying the check valve is not bad only that I dont believe thats the reason for the headlights to pop up.The only time you really need the check valve is when the vacuum is low due to wide open throttle or you shut the engine off and you want the lights to come up.
Hurri whether you replace the valve or not make sure you replace the little white filter thats in between the valve and the manifold.This filter protects the 3 port metal check valve from engine contaminants.
Last edited by ...Roger...; Oct 22, 2008 at 02:11 PM.
Race Director
Joined: May 2006
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From: Dayton, Ohio
Melting Slicks
Joined: Sep 2007
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From: Tucson AZ
Pay attention to this man, he's on the money. I fooled with the same problem for 5 nights in a row before I found out that I had a small leak. I just replaced all the hoses with a kit. My headlights open in about 3-4 secs now, both at the same time too. Tank