Boost Gauge... is This Normal!?
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This is a discussion on Boost Gauge... is This Normal!? within the General Maintenance, Troubleshooting & Accidents. forums, part of the Tech & Modifying & General Repairs category; I just installed a boost gauge on my 02 WRX and when I start my car it goes from 0 ...

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    Exclamation Boost Gauge... is This Normal!?

    I just installed a boost gauge on my 02 WRX and when I start my car it goes from 0 to like between 20-10 and stays there normally on about 18 while my car is just sitting there idling.. But when I push the gas to test it.. it goes from where its sitting (about 18lbs on the left side of 0) to like 0 or 1-2lbs on the right side of 0.. I thought it was going to be sitting at 0 until I pushed the gas is this normal? But when I took it for a drive test it still was sitting to the left of 0 at about 20-17lbs but when I start driving and give it some gas it seems to give a good reading going from 5-13lbs on the right side of 0... but it never sits at 0... is something not right?

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    He simply abides. SD_GR's Avatar
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    You are reading vacuum and boost. Their units are different. Look closely at the gauge. Sounds normal.
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    So is it normal for the gauge to not be sitting on 0 while sitting there idling? I always thought it should be at 0 when sitting still idling or sitting at a red light or whatever..

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    Yes it's normal.
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    Ok.. Im getting told 2 different things here lol I just got back from the Advanced Auto Parts store and the guy I talked to there said that the gauge should be reading 0 when idling... And that if its not reading 0 when idling that I have a leak in the vac system somewhere prob where I tee'ed in or maybe where the little hose connects to the gauge... So who is right n who is not lol?

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    Why did you go to a crappy auto parts store for advice when your question was already answered here?

    The grease monkey at the parts store is wrong. At idle, the car will read vacuum, since it is sucking in less air pressure than ambient. When you press the gas pedal, the needle will rise toward zero as the pressure in the manifold equalizes with ambient. Once the turbo spools up, the manifold will positively pressurize.

    If your gauge reads zero at idle, you would have a massive intake leak.
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    Quote Originally Posted by Clarkiss View Post
    Ok.. Im getting told 2 different things here lol I just got back from the Advanced Auto Parts store and the guy I talked to there said that the gauge should be reading 0 when idling... And that if its not reading 0 when idling that I have a leak in the vac system somewhere prob where I tee'ed in or maybe where the little hose connects to the gauge... So who is right n who is not lol?
    Bahahahaha omg you are trusting some guy from Advance Auto parts?? Lmao!


    You don't idle at atmospheric pressure. If you did, none of your vacuum operated components would work, would they?
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    Quote Originally Posted by Clarkiss View Post
    Ok.. Im getting told 2 different things here lol I just got back from the Advanced Auto Parts store and the guy I talked to there said that the gauge should be reading 0 when idling... And that if its not reading 0 when idling that I have a leak in the vac system somewhere prob where I tee'ed in or maybe where the little hose connects to the gauge... So who is right n who is not lol?
    hahahahaha, that guy doesn't have to slightest clue what the **** he is talking about. What you are seeing is normal. Read up on how boost gauges actually work. When you are idling you should be seeing somewhere in the park of 20lbs of vacuum (left side of zero). Then when you are driving under heavy gas pedal load you will start seeing some boost numbers (right side of zero).
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    Quote Originally Posted by McBill View Post
    hahahahaha, that guy doesn't have to slightest clue what the **** he is talking about. What you are seeing is normal. Read up on how boost gauges actually work. When you are idling you should be seeing somewhere in the park of 20lbs of vacuum (left side of zero). Then when you are driving under heavy gas pedal load you will start seeing some boost numbers (right side of zero).
    Lol -20 psi of vacuum is unrealistic. Standard atmospheric pressure is 14.5 psi, which would mean you are less than a complete vacuum. Usual idle is -9 psi of vacuum (approx 5 psi absolute pressure).
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    Quote Originally Posted by Clarkiss View Post
    I just installed a boost gauge on my 02 WRX
    What gauge do you have and did you not read the ibstructions that came with it?
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    Hey guys lets get something straighten out right now im NOT AGAIN NOT trusting or listening to the dude at the auto parts store I was just maintaining a open mind like I do with everything I do so .. haha I 100% trust most of what I see on here and most of the members.. I just happened to be passing the auto place and decided to stop in and see what they had to say lol.. Im glad to hear this is normal tho So I guess my question would be now what is normal for a 02 WRX while not on the gas pedal?


    Quote Originally Posted by Donkey View Post
    What gauge do you have and did you not read the ibstructions that came with it?
    Yes I did and everything is right just wanted to kno if I should be sitting at 0 or not

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    Quote Originally Posted by Clarkiss View Post
    So I guess my question would be now what is normal for a 02 WRX while not on the gas pedal?\
    Quote Originally Posted by zax View Post
    Usual idle is -9 psi of vacuum (approx 5 psi absolute pressure).

    More vacuum is possible when the car experiences negative load (engine braking).
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    Again, what units are you measuring? See info, this thread, however vac is sometimes not stated in PSI, thus affecting your answer.
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    Dorp, I just realized you're probably reading in inches of Mercury. 20 inches of mercury is between 9 and 10 PSI.

    Quote Originally Posted by McBill View Post
    hahahahaha, that guy doesn't have to slightest clue what the **** he is talking about. What you are seeing is normal. Read up on how boost gauges actually work. When you are idling you should be seeing somewhere in the park of 20lbs of vacuum (left side of zero). Then when you are driving under heavy gas pedal load you will start seeing some boost numbers (right side of zero).
    2015 CWP WRX STi ... But how did I get roped back into an EJ motor?!
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