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Old 05-17-2013, 07:16 PM   #1
rg3indc
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Member#: 356736
Join Date: May 2013
Default Knocking/Underboost

My car is an 02 USDM WRX, basic stg. 2 setup with an opensource tune.

When I had my car initially tuned we encountered a few problems. The tuner was unable to get my car to hit the target boost of 16psi, only amounting to 14 psi. Using a different restrictor pill the car had wavering boost which spiked around 19psi but was obviously not going to work. During this run it was also apparent the clutch was slipping.

Tuner said I should replace front O2 sensor and it would work. Did that, removed the stuttering, but still underboosting. Says to tighen wastegate. I did that, maybe 3-4 times, though only a rise in maybe 0.5psi in boost. I replaced the IC to throttle body tube with an aftermarket unit, did not make a difference.

Since my tune I have had a new clutch and lightweight flywheel installed.

I go to datalog the other day and notice I have pretty bad FLKC. My datalogs and Learning view are attatched. I could not pull my ROM because I only have a BFM cable.

What could be the causes of this knock? A fixed boost leak that was previously tuned for? A new boost leak that was not accounted for in the tune? Blown turbo? The turbo whistle seems to be much louder than a friends vf39 wrx.

I am not looking for anyone to fix my car, I want to do that myself, but I would like to know what direction I should start going in. Im hoping that someone can look at my data and make an educated guess what went wrong. Thanks.

https://dl.dropboxusercontent.com/u/.../LV%20Log1.png

https://dl.dropboxusercontent.com/u/101225549/out3.xls
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Old 05-17-2013, 10:15 PM   #2
JonnyV2889
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Member#: 197384
Join Date: Dec 2008
Chapter/Region: NESIC
Location: MWV NH
Vehicle:
2006 WRX Ltd
OBP

Default

Are you running a cai/sri? You maf scaling is either botched or you have a leak somewhere for starters.
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Old 05-17-2013, 10:27 PM   #3
rg3indc
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Default

I figured I either have a leak or I accidentaly fixed a leak. My only mods that would affect the powertrain are a catless downpipe, SPT catback,removed silencer, throttle body to IC silicon tube, and a lightweight flywheel.
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Old 05-18-2013, 06:41 AM   #4
JonnyV2889
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Member#: 197384
Join Date: Dec 2008
Chapter/Region: NESIC
Location: MWV NH
Vehicle:
2006 WRX Ltd
OBP

Default

I'd start with testing for a leak, if all checks out then your maf needs to be rescaled, since you're on stock injectors.

* Clean your maf before you go rescaling it.
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Old 05-18-2013, 02:12 PM   #5
rg3indc
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Default

Would my logs indicate a vaccum leak or a boost leak? Is there any indication looking at my logs whether the leak is pre or post turbo?
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Old 05-19-2013, 04:27 PM   #6
nmlittlebigman
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Join Date: May 2012
Chapter/Region: SWIC
Location: Arrey, NM
Vehicle:
2011 WRX STi Sedan
WRB Stage II T.P. tuned

Default

Quote:
Originally Posted by rg3indc View Post
Would my logs indicate a vaccum leak or a boost leak? Is there any indication looking at my logs whether the leak is pre or post turbo?
AF learning #1 A, B,C,D stored fuel trims can sometimes indicate where the leak might be but you might as well build and use a leak tester and find out for sure. You don't need alot of pressure to find leaks. Usually less than 10 psi and soapy water does the trick.

http://forums.nasioc.com/forums/show....php?t=2205161
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Old 05-21-2013, 08:43 PM   #7
danger1138
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Member#: 279525
Join Date: Apr 2011
Location: QUEENS NY
Vehicle:
04 rex luger!

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Yea follow everyones advice and build your self a boost leak tester before u go spending money elsewhere. Very simple. I was hesitant at first, once i built one and tested the intake tract i found minor leaks at the maf (changed o ring, fixed problem), fuel pressure regulator (swapped over a new vac hose, problem solved), and at the bpv gasket (new gasket did the trick). Also make sure u zip tie all vac lines just to be sure.
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Old 07-11-2013, 08:53 PM   #8
rg3indc
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Member#: 356736
Join Date: May 2013
Default

I finally got around to performing a boost leak test after getting my car back (accident).

I cannot seem to build any pressure in the intake?!? I uncapped and plugged the three holes of the turbo inlet. Am I missing something??

Also I finally got a cable that works with ecuflash. Comparing my ROM to the stock ROM, the MAF scaling table is exactly the same. So I believe it is not a MAF scaling issue.
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