Vacuum gauge
Thread Starter
Pro
Joined: Dec 2004
Posts: 710
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From: Raynham MA
Vacuum gauge
I bought a new vacuum gauge from Harbor Freight. I've neever used one before. When I plug it into the vacuum line on the back of my carb that the lines for the headlights go into it reads the vacuum but its a little erratic. It quickly fluxuates between 7-12. Is that normal?
Melting Slicks
Joined: Dec 2006
Posts: 2,669
Likes: 3
From: Kingston Ontario
Vacuum reading should be steady, at a constant RPM, in order for proper engine assessment.
Fluctuation means leak(s) in the vacuum system, ie: weak springs, leak at components, hoses or connections.
Fluctuation means leak(s) in the vacuum system, ie: weak springs, leak at components, hoses or connections.
Safety Car
Joined: May 2008
Posts: 3,747
Likes: 713
From: Lafayette Louisiana
Article on vacuum gauge
Here is an article on vacuum gauge use that I thought was pretty good.
http://www.secondchancegarage.com/public/186.cfm
Hope this helps.
(Nice classic white 76!)
http://www.secondchancegarage.com/public/186.cfm
Hope this helps.
(Nice classic white 76!)
Last edited by 20mercury; Sep 12, 2010 at 10:41 AM.
Advanced
Joined: Jan 2010
Posts: 56
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From: manhasset n.y.
If you think you have a vacuum leak around the intake manifold
with the engine running take a pronane tourch turn it on(NOT LIT).Poke it around the intake manifold.If engine RPM rises at a certain spot you have found a potential vacuum leak
with the engine running take a pronane tourch turn it on(NOT LIT).Poke it around the intake manifold.If engine RPM rises at a certain spot you have found a potential vacuum leak
Thread Starter
Pro
Joined: Dec 2004
Posts: 710
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From: Raynham MA
Yes, My mechanic said he thought my intake manifold was leaking a little. So sounds like this could explain wehy my vacuum reading is erratic, cars bogs and stalls sometimes and just doesnt feel that "crisp"????
Team Owner
Joined: Jan 2006
Posts: 37,637
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From: Crossville TN
You can locate the source of any intake-to-head leaks by shooting little puffs of carb cleaner at selected locations at that gasket and listening for rpm increases on the idling engine.
To find the vacuum level your engine [present condition...gasket leaks or not] is capable of producing, remove the main vacuum line from the manifold and hook up the gauge in its place. That will eliminate any leakage in the vacuum system lines {which you removed}. Don't forget that you also [may] have a vacuum advace can on the distributor and/or a vacuum booster line for the power brake system. If your vacuum readings are still low after you pull the other systems off, you may need to remove the vacuum feed lines (and plug them) for the dist advance and/or the brake booster to verify they are not the source of your problems.
To find the vacuum level your engine [present condition...gasket leaks or not] is capable of producing, remove the main vacuum line from the manifold and hook up the gauge in its place. That will eliminate any leakage in the vacuum system lines {which you removed}. Don't forget that you also [may] have a vacuum advace can on the distributor and/or a vacuum booster line for the power brake system. If your vacuum readings are still low after you pull the other systems off, you may need to remove the vacuum feed lines (and plug them) for the dist advance and/or the brake booster to verify they are not the source of your problems.
Thread Starter
Pro
Joined: Dec 2004
Posts: 710
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From: Raynham MA
My mechanic said my engine only pulls 7 at idle. I'll verify this but that's too low right? I believe he took the reading from the PCV valve. He said this may have something to do with a heavy CAM.
