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Old 01-21-2010, 11:28 AM   #1
prophet03
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Default Boost pressure starting at -20 psi, peaking at 5 psi...whats wrong?

i have an 03 wrx that didnt have a boost gauge on it when i bought it, i only recently got a gauge and it is only giving me a maximum reading of 5 or 6 psi. im wondering if its the boost controller thats holding it back, but its the stock controller, and my utec has the stock settings on it... it also takes a while for the boost to get to positive psi. my mechanic said to take the wastegate hose off and see if the pressure builds fast, in which case get off the gas. thats fine, but how do i fix it then if that happens.
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Old 01-21-2010, 12:00 PM   #2
IAmTheSleepySubie
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is it a decent boost gauge cause the gauge you got could be bad.

any other mods on the car?

and is that 5 psi at full throttle?

if i stay under 1/4 throttle or so it stays right about 5psi
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Old 01-21-2010, 04:15 PM   #3
Concillian
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Wastegate boost should be at least 8-10 psi. Sounds like your gauge is screwed up. Especially if it's really reading -20psi at any time (-20psi is physically not possible,) though I suspect you're misreading the units, it should be +20mmHg vacuum, not -20psi.

If you have a UTEC, presumably someone tuned it at some point? They should have calibrated the MAP readings when they did it. Log the UTEC and what does it say for boost pressure? If you're at approx sea level, even the UTEC's default calibration should be close enough to tell the difference between 12 psi (stock boost) and 5-6 psi. Log and look at WOT ~4kRPM.
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Old 01-21-2010, 04:17 PM   #4
rkramer
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stock boost controller? you mean the ecu? sounds like you are dealing with someone else's halfass returned to stock hack job.

I wouldn't take the wastegate hose off and run. It only takes a split second to ruin an engine. one thing to consider, with the stock turbo, the wastegate spring is at least 7 psi. you should hit that no matter what your controller (either the ecu or standalone) is trying to do. There is simply no way to open the wastegate at a lower pressure.
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Old 01-21-2010, 06:56 PM   #5
prophet03
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i thought about it being a bad gauge, but aparently its supposed to make vaccuum at idle, but 20? 5 psi at full throttle and no, the boost controller is separate from the ecu, ecu controlls the boost controller. anyway, wats the probable cause for it? more than likely the gauge?
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Old 01-21-2010, 07:03 PM   #6
drummerboy827
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Can't believe no one's asked the obvious yet..

How's the car running?

If your engine was actually only getting 5 psi of boost from the turbo, you would know. It would be slowwwww...
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Old 01-21-2010, 07:10 PM   #7
UkNuck
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It would help if you could post some details:

o what brand and type (mechanical? electrical?) of gauge is it?

o where did you tee off?

o what units does your gauge read in? a value of -20 would be about right for vacuum at idle in inches of mercury (in-Hg)

o what conditions are you measuring the boost? you need a good bit of load (e.g. a hard 2nd gear pull) to hit full boost
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Old 01-21-2010, 07:22 PM   #8
prophet03
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I have headers, upipe, tbe, intake, turboxs utec, thats about it. i hope its just the gauge, so its easy and cheap
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Old 01-21-2010, 07:26 PM   #9
prophet03
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the engine runs fine, its just as you said slow at higher rpms, 3500+. its a prosport mechanical gauge, measuring boost in all gears, reaches max psi in 3rd, 4th, and 5th. yea sorry, just easier to write -20 psi lol, yes, 20 in-Hg
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