New Boost Gauge - Vacuum at IDLE?
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This is a discussion on New Boost Gauge - Vacuum at IDLE? within the General Maintenance, Troubleshooting & Accidents. forums, part of the Tech & Modifying & General Repairs category; I just got an SPT boost gauge installed and at idle, it reads about 18-20 inHg - is that the ...

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    Registered User hieu1004's Avatar
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    New Boost Gauge - Vacuum at IDLE?

    I just got an SPT boost gauge installed and at idle, it reads about 18-20 inHg - is that the normal range?

    I know altitude/elevation can also affect the reading, but do accessories like the radio, etc also affect it?

    Thanks!
    Stink-eye Mob #1004

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    When the engine is healthy and working correctly , at idle the needle should be steady and within the range of 17 - 22 inHg
    '02 WRX 4EAT, 311,000KMs/194,500Miles, Sold. Best car I ever had. '09 STi stage 1, hope this one will be good too...

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    Registered User EvoEatr's Avatar
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    Quote Originally Posted by hieu1004 View Post
    I just got an SPT boost gauge installed and at idle, it reads about 18-20 inHg - is that the normal range?

    I know altitude/elevation can also affect the reading, but do accessories like the radio, etc also affect it?

    Thanks!
    As mentioned a steady reading of -17 to -22 in. at idle is normal...the only accessory that might affect it is one which ups your idle a tad such as switching on the AC or when the fans kick on however it only ups your idle by a few hundred RPM's if that so it shouldnt affect your engine vacuum my much if even at all...

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    Registered User hieu1004's Avatar
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    That's good to know. Thanks for the replies, this is my first turbo car and so I am still learning.
    Stink-eye Mob #1004

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    Registered User Willard's Avatar
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    All engines will have Vac at idle. If you hook a boost gauge to an N/A engine and mash the gas the needle will only go to 0 or near 0. On an F/I turbo or S/C engine the needle fly by 0 and get into positive manifold pressure, or boost, and stop at the wastegate or pulley setting. There are other variables but thats the basics of it.
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    Registered User shello007's Avatar
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    My Gauge's Erroneous reading

    My Gauge used to read 20 inHg. Then it went to 15. After uppipe install (maybe a month or two afterwards) it's idlng at 12 inHg. Please help. Is it a vacuum leak or a pressure difference on the exhaust?

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    Moderator Donkey's Avatar
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    Quote Originally Posted by shello007 View Post
    My Gauge used to read 20 inHg. Then it went to 15. After uppipe install (maybe a month or two afterwards) it's idlng at 12 inHg. Please help. Is it a vacuum leak or a pressure difference on the exhaust?
    Probably a vacuum leak or a borked gauge.
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    Registered User hieu1004's Avatar
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    ^^^^^ What he said. Check all hoses real carefully.
    Stink-eye Mob #1004

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    i just bought my 06 wrx and it has the mpa boost gauge on the steering column and i think i may be very much mistaken but at max boost its only reading .06 mpa and my understanding is it should be reading around the .08 - .09 range.... is this right or am i way off the mark?

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