Hiss from under my dash?
Thread Starter
Racer
Joined: Jan 2000
Posts: 472
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From: Warren NJ
Hiss from under my dash?
I hear a loud hiss (vacuum leak?) coming from under the driver's side dash. I poked my head under there and did not see any loose hoses.
Any thoughts?
PS - my car is stumbling and hesitating when I drive it. Could these be related? (Just got the car back from the body shop where it has been sitting most of 6 months other than being moved around their lot.)
:banghead:
Any thoughts?
PS - my car is stumbling and hesitating when I drive it. Could these be related? (Just got the car back from the body shop where it has been sitting most of 6 months other than being moved around their lot.)
:banghead:
Race Director
Joined: Dec 1999
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Re: Hiss from under my dash? (DaddyO)
Headlight vac override switch (pull down **** under steering column) leking or one of the hoses is loose. Could also be the vacuum hose on the cruise control disengage switch (behind brake pedal, there are 2 switches, one is for the brake lights and doesn't have a vac. hose on it)
Melting Slicks
Joined: Jan 2003
Posts: 2,804
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From: OKC Oklahoma
Re: Hiss from under my dash? (Twin_Turbo)
Headlight vac override switch (pull down **** under steering column) leking or one of the hoses is loose. Could also be the vacuum hose on the cruise control disengage switch (behind brake pedal, there are 2 switches, one is for the brake lights and doesn't have a vac. hose on it)
Team Owner
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From: Exiled to Richmond, VA - Finally sold my house in Murfreesboro, TN ?? Corner of "Bumf*&k and 'You've got a purdy mouth'."
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St. Jude Donor '06-'10, '13
Re: Hiss from under my dash? (79VetteMike)
Yeah - vac problem somewhere, and that is why your car runs badly.
I had a backfire on mine blow some hoses off and the car went to really lean and running like garbage until I could pull it over and fix the mess.
I had a backfire on mine blow some hoses off and the car went to really lean and running like garbage until I could pull it over and fix the mess.
Team Owner
Joined: May 2001
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From: Exiled to Richmond, VA - Finally sold my house in Murfreesboro, TN ?? Corner of "Bumf*&k and 'You've got a purdy mouth'."
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St. Jude Donor '06-'10, '13
Re: Hiss from under my dash? (DaddyO)
Oh great......at least I have a one of those mity vac pump and gauges to help me along.
What is the first step in vac system diagnosis?
What is the first step in vac system diagnosis?
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Team Owner
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From: Exiled to Richmond, VA - Finally sold my house in Murfreesboro, TN ?? Corner of "Bumf*&k and 'You've got a purdy mouth'."
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Re: Hiss from under my dash? (DaddyO)
well, my 1980 is different.
I have on that comes in on the drivers side that is used for the cruise control and another for the headlight system.
I think there is a small on on the passenger side that goes to the a/c system to control the vents.
I have on that comes in on the drivers side that is used for the cruise control and another for the headlight system.
I think there is a small on on the passenger side that goes to the a/c system to control the vents.
Instructor
Joined: May 2003
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From: Edwards CA
Re: Hiss from under my dash? (DaddyO)
Maybe the first thing I would do is plug the vacuum line running off the manifold. This way you could tell if the engine is stumbling from a vacuum leak from this line to begin with. I would check with a vacuum gauge with this line plugged and unplugged. You could have a different vacuum leak and a leak under the dash. Then go to isolating it from there.
Race Director
Joined: Mar 2001
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From: Living in the Hartland
Re: Hiss from under my dash? (DaddyO)
It is the one coming of a port right behind the carb. You can use a squeeze clamp to make it easier. Try starting your car and letting settle into a warm idle then use the clamp to pinch the hose right after it exit the manifold port, if the car smooths out and you loose your hiss noise then you have found a leak. Unfortunetly you then have to figure which hose is leaking under the dash. :(
Le Mans Master
Joined: Apr 2001
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From: Was New Orleans but swam to Baton Rouge LA
Cruise-In IX Veteran
Re: Hiss from under my dash? (DaddyO)
A good cigar and a spotter work well for tracing vacuum leaks. I just blew smoke into the lines and had someone look for the smoke. I eventually found out I had some bad relays. I still need to trouble shoot the inside of the car. I have a feeling the heater door relay valve has a leak, or maybe the vent controls inside.
Burning Brakes
Joined: Jul 2000
Posts: 963
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From: melbourne,Australia
Re: Hiss from under my dash? (DaddyO)
The hoses can split where they connect to the headlight switch and where they connect to the override switch,they look ok and seem to be in position but still leak,look at the dip switch connection as well......john :chevy
Thread Starter
Racer
Joined: Jan 2000
Posts: 472
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From: Warren NJ
Re: Hiss from under my dash? (jdunne)
Thanks to everyone for the advice. It's definitely a vacuum leak. When I clamp the vac line that comes from the manifold and goes to the vac system, the car runs much smoother.
Can I drive the car with that line closed off? Does it only go the the lights, wipers and heating system?
Can I drive the car with that line closed off? Does it only go the the lights, wipers and heating system?
Team Owner
Joined: Jul 1999
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From: Huntersville NC
Re: Hiss from under my dash? (DaddyO)
Can I drive the car with that line closed off? Does it only go the the lights, wipers and heating system?
Melting Slicks
Joined: Feb 2001
Posts: 2,562
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From: (Temporarily) Colorado Springs Colorado
Re: Hiss from under my dash? (DaddyO)
You might want to check this link out ... http://vetteworks.tripod.com/techdocuments/Vaccum.html . Also I have a very nice PDF drawing of the whole system and all of its componets. Let me know and I can email it to you.