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Old 04-06-2013, 04:33 PM   #1
Bryan82
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Default Erratic Vacuum Gauge Reading, Please Help **Video Inside**

Okay, so I decided to throw a vacuum gauge on my WRX just to see what the results would be. Needless to say, they are less than comforting. Can anyone help me out on interpreting these readings. I think, I am leaning towards weak valve springs, or valves themselves.

Mods list:
Gutted up pipe
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Compression test was at ~155-165 PSI.

Thanks in advance!

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Old 04-06-2013, 08:54 PM   #2
Uncle Scotty
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cant see the vid at work...but erratic vac is usually a leak or valve issue
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Old 04-06-2013, 10:07 PM   #3
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Originally Posted by Uncle Scotty View Post
cant see the vid at work...but erratic vac is usually a leak or valve issue
I hope you can get to watch it later and then let me know your thoughts. I have never encountered such a crazy looking vacuum reading. I had to go look up what it may be. Essentially it does a 1 in Hg vibration at idle, then when at fast idle maybe 1500-2500 RPM the needle is rapidly oscillating between ~ 12 in Hg- ~ 22 in Hg. The needle moves so fast between this range it is blurred.
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Old 04-06-2013, 10:25 PM   #4
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Originally Posted by Bryan82 View Post
I hope you can get to watch it later and then let me know your thoughts. I have never encountered such a crazy looking vacuum reading. I had to go look up what it may be. Essentially it does a 1 in Hg vibration at idle, then when at fast idle maybe 1500-2500 RPM the needle is rapidly oscillating between ~ 12 in Hg- ~ 22 in Hg. The needle moves so fast between this range it is blurred.
valve issues i think
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Old 04-06-2013, 11:04 PM   #5
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Yeah, everything I am reading points me to valve springs. But, I like to "home run" car problems, so, rebuilt heads here I come. Cha ching!!, lol
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Old 04-07-2013, 11:53 PM   #6
Bryan82
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I originally took the vacuum reading that is seen in the video from the brass nipple on the front of the intake manifold.

Today, I hooked the vacuum gauge up to the bypass valve, and upon doing so, the readings were much more normal. Now pulling about -18 in Hg at idle(needle still shaky), and at fast idle the vacuum is steady at over -20 in Hg.

Any thoughts anyone?
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Old 04-08-2013, 06:46 AM   #7
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Could of been where you were plumbing into
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Old 04-08-2013, 10:38 AM   #8
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More than likely you had it reading from a bad spot, before I read that far down in the thread I was going to tell you to pick it up somewhere else and check.
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Old 04-08-2013, 08:33 PM   #9
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Quote:
Originally Posted by Bryan82 View Post
I originally took the vacuum reading that is seen in the video from the brass nipple on the front of the intake manifold.

Today, I hooked the vacuum gauge up to the bypass valve, and upon doing so, the readings were much more normal. Now pulling about -18 in Hg at idle(needle still shaky), and at fast idle the vacuum is steady at over -20 in Hg.

Any thoughts anyone?
fsm states that the vac at idle with all accessories off and engine at operating temp should be less than 17.72in-Hg.....so yeah...18in-Hg is good
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