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Old 01-11-2021, 03:50 PM   #1
mikeford
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Default My boost gauge and Accessport don't agree. At all.

TLDR: Accessport shows boost, gauge doesn't. Both show vacuum.

I picked up a 2005 WRX with a very blown head gasket. I pulled the motor and freshened up everything. It runs well, but I think I've had turbo problems the whole time.

Since I've gotten it running again, there is never any boost on the gauge, but it shows vacuum and that correlates with the Accessport. The Accessport will show boost up to 22 psi (throwing an overboost code in the ECU and cutting power.)

I figured my analog gauge was bad, so I replaced it. The new analog gauge also shows vacuum, but no boost. Aiming my air compressor shows both gauges are capable of showing boost, ie, they're not broken. Putting my finger over the turbo line, I feel vacuum, no matter the rpm I open the throttle to. The line will not blow away from my finger. I checked at 2 different lines, one right on the aluminum intake manifold.

What is going on, because I'm completely baffled?

Edited to add: the analog gauges go to zero when boost should be (is according to the Accessport) building. The just never go above zero.
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Last edited by mikeford; 01-11-2021 at 07:20 PM.
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Old 01-11-2021, 03:56 PM   #2
whozatguy
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No codes? Where is the gauge pulling the air from? May have mixed up some vacuum lines during reassembly.
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Old 01-11-2021, 04:03 PM   #3
mikeford
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Quote:
Originally Posted by whozatguy View Post
No codes? Where is the gauge pulling the air from? May have mixed up some vacuum lines during reassembly.
No codes.

The gauge line is Teed into the stock BOV line.
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Old 01-14-2021, 04:21 PM   #4
Whooopasss
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check the vacuum line.. maybe it has on of them one-way valve. like these https://www.siliconeintakes.com/imag...Check-Main.jpg
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Old 01-14-2021, 05:30 PM   #5
rtv900
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Quote:
Originally Posted by mikeford View Post
Putting my finger over the turbo line, I feel vacuum, no matter the rpm I open the throttle to. The line will not blow away from my finger.
are you talking about standing in your garage with your finger on that line and winging the throttle to see if you feel "boost" in that line?

If so you are never going to build boost just winging a throttle in neutral, never going to happen.
It will basically just dip vacuum to zero and then instantly pull vacuum again because it's impossible to do that in neutral.

I'm not sure what your issue is, but that test method is useless.
I mean, you must know if you have boost when you drive, so it sounds like you know you have boost, it's just a gauge issue.

So check out your connection line.
Can you suck air through that line and blow into it also to ensure it is working both ways?
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Old 01-15-2021, 04:38 PM   #6
subaru_gc8
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Quote:
Originally Posted by mikeford View Post
No codes.

The gauge line is Teed into the stock BOV line.
but you sad you get an over boost code?

personally I would go with the ap, gauges are known to be wrong
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Old 01-21-2021, 09:40 AM   #7
mikeford
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I think I figured it out. The MAP sensor is aftermarket, and I'm not even sure it's for a WRX. I put a good, used MAP sensor on, and now the computer and gauges are in agreement. Thank you.
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