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Old 12-29-2010, 11:31 PM   #1
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Default Vacuum gauge questions

Trying to tune my Megasquirt and I found an interesting problem. When I crack the throttle my vacuum gauge increases from 18inHg to 22inHg, then goes up when the throttle opens more. Could be a problem?
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Old 12-30-2010, 01:25 AM   #2
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I'm not exactly sure what you mean, but my car idles at about 21inHg Vacuum. If you're saying that the more your throttle is open, the more vacuum it pulls; then there is something wrong.
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Old 12-30-2010, 02:07 AM   #3
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Yes I think so,What I mean is the vacuum increases for a second or two from 18-22 then starts going in the right direction the more throttle is given. I am going to confirm with Megasquirt gauge tomorrow. Very strange.
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Old 12-30-2010, 01:01 PM   #4
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What does everyone think of my problem in relation to the 3rd paragraph in this article about MAP sensors. I could be on to something as I never noticed this breaking in my engine on factory management the last two weeks...unless I'm completely off base here.

http://www.aa1car.com/library/map_sensors.htm
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Old 12-30-2010, 01:20 PM   #5
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"When conditions change and the vehicle is cruising along under light load, coasting or decelerating, less power is needed from the engine. The throttle is not open very wide or may be closed causing intake vacuum to increase. The MAP sensor senses this and the computer responds by leaning out the fuel mixture to reduce fuel consumption and advances ignition timing to squeeze a little more fuel economy out of the engine."

If that is what you meant, here's my take. If I start my car and it idles, it's pulling about 21inHg. If I am going down a big hill and I'm off the throttle sometimes it'll pull 24inHg.
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Old 12-30-2010, 06:44 PM   #6
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Ok so I had a vacuum leak causing 18inHg instead of 22inHg at idle and then, cracking the throttle pulled more vacuum down to 22inHg. Applying more throttle pushed the vacuum up to 0-ish, Still cant figure this out...I need vacuum gauge numbers from all you low compression turbo guys running megasquirt

Last edited by JEMERY; 12-30-2010 at 09:22 PM.
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Old 12-31-2010, 02:04 AM   #7
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Is this on your standalone boost gauge or on your kpa gauge on ms?

When you step on the gas it should go up towards the 0 and then slowly go down to 20ish in. as the engine speeds up to the target speed.

Where is your vac gauge connected to?
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Old 12-31-2010, 02:21 AM   #8
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The ms is comparable to the external vacuum gauge. Both fluxuate the same so I don't think it's vacuum oriented.
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Old 12-31-2010, 02:22 AM   #9
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I need someone in the atl who knows troubleshooting to help me out!!!
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Old 12-31-2010, 02:48 AM   #10
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Where did you say your vac gauges were connected to? As in location of the manifold.
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Old 12-31-2010, 02:55 AM   #11
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I tee'd off of the fpr vacuum line.
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