Vacuum Readings - Team Camaro Tech
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post #1 of 9 (permalink) Old Mar 4th, 02, 12:55 PM Thread Starter
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I am showing some erratic readings on the vacuum gauge. I am pulling qbout 11" at idle but there is about a 1" fluctuation in either direction at idle.

Would a small fluctuation like this be cause for concern? In other words, a major mechanical problem?

I am trying to diagnose and idle problem I have had for sometime and it's my understanding this gauge should read STEADY at idle, no bouncing around, dropping etc.

-Funk
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post #2 of 9 (permalink) Old Mar 4th, 02, 01:57 PM
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What are your cam specs? My cam has a lot of overlap (both valves open at the same time) and my vacuum gauge jumps around at idle. The vacuum increases and smooths out once I increase the RPM, so I figured it's normal. I'll keep watching this post to see if maybe I have a problem as well. Good luck.
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post #3 of 9 (permalink) Old Mar 4th, 02, 02:07 PM Thread Starter
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I couldn't tell ya the specs. The previous owner has no clue, even though he rebuilt the motor .

Mine is the same way, give her some juice and the vacuum climbs and is smooth.

-Funk
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post #4 of 9 (permalink) Old Mar 4th, 02, 03:00 PM
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Greetings CFunK,
With this fluctuation you mention, is your RPM gauge fluctuating up and down? I had an '85 Z28 with this problem once, idle fluctuated constantly. Almost (?:confused drove me nuts, checked everything and then some. Solved problem by accident, changed my brake pads one day and bled the brake system. The fluctuation disappeared and never came back. Before you start scratching your head and wondering if I've lost my marbles, let me tell you the rest of the story. It seems that an overly ambitiuos, but not overly intelligent mechanic decided that the best way to clean an O2 sensor was to pull the vaccuum check valve from the power booster while the engine was running and rev the engine for a couple of minutes before replacing the check valve. This offset the piston in the power booster, when I bled the brakes, the piston re-seated itself back to its original position. Just a thought.
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post #5 of 9 (permalink) Old Mar 4th, 02, 03:38 PM
 
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I had the same erratic vacuum readings on my 454 which only has the Performer cam in it, not too radical. To dampen the readings (so my new vacuum gage wouldn't beat itself to death) I just took a small C-Clamp and tightened it on the vacuum line at a convenient place until the pulsations stopped. Presto, no more pulsations. Scott
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post #6 of 9 (permalink) Old Mar 5th, 02, 05:18 AM
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<BLOCKQUOTE>quote:</font><HR>Originally posted by ssfrebo:
I had the same erratic vacuum readings on my 454 which only has the Performer cam in it, not too radical. To dampen the readings (so my new vacuum gage wouldn't beat itself to death) I just took a small C-Clamp and tightened it on the vacuum line at a convenient place until the pulsations stopped. Presto, no more pulsations. Scott<HR></BLOCKQUOTE>


Good trick? Any negative reprocussions to doing this?
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post #7 of 9 (permalink) Old Mar 5th, 02, 07:09 AM
 
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I've been using this C-Clamp "dampener" for about three years now. The $0.99 C-clamp is still under the dash somewhere, don't remember where. I have never adjusted it. There is no lag in response time on the gauge with the C-Clamp dampener, i.e. it is very responsive to throttle position, can't tell a difference from previous vehicles with factory cams, etc. No signs of a negative affect on the gage at all. Scott
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post #8 of 9 (permalink) Old Mar 5th, 02, 04:47 PM
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<BLOCKQUOTE>quote:</font><HR>Originally posted by ssfrebo:
I've been using this C-Clamp "dampener" for about three years now. The $0.99 C-clamp is still under the dash somewhere, don't remember where. I have never adjusted it. There is no lag in response time on the gauge with the C-Clamp dampener, i.e. it is very responsive to throttle position, can't tell a difference from previous vehicles with factory cams, etc. No signs of a negative affect on the gage at all. Scott<HR></BLOCKQUOTE>

Hmmmm interesting. I get a little fluctuation at idle on mine, .5" either way. (9.5-10.5)

I have a mild cam on my 454.
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post #9 of 9 (permalink) Old Mar 6th, 02, 06:39 AM
 
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Mike...have you got the clamp cinched down far enough on the vacuum line. Also, I believe I am using a VDO gauge...if that makes a difference.
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