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Old 04-20-2006, 09:52 PM   #1
bugeyes
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2001 V7 sti

Default boost oscillation problem

The first thing your going to say is ECU or boost map. Well.......
I do not have any electronic boost control. My wastegate is connected directly to the turbo outlet. I did this to try and isolate possible causes. Normally I run a pneumatic boost control which has no ecu or electronic input. Needless to say with or without the boost control the problem doesnt change or go away.
I have a external wastegate 36mm and a GT30 turbo. Very low backpressure exhaust and no cat. Big FMIC.
My boost starts to oscillate +-3psi as soon as the wastegate starts to open.
I have tried the following and have not been able to fix it.
Blocked off the BOV.
Connected the wastegate diaphragm to the intake manifold instead of turbo.
Placed a restrictor in the wastegate control line in order to try and smoothen the pressure.
Moved my data logger maniufold pressure tube to another place on the plenum.
I'm tending to point the finger at changing the wastegate but I'd rather get some feedback before going to that extreme.
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Old 04-21-2006, 09:31 AM   #2
JRSCCivic98
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Have you checked for general leaks after the turbo... like on the clamps for the FMIC and such?
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Old 04-21-2006, 11:14 AM   #3
corey_dyck
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Clean the boost control solenoid, it gets gummed up and causes exactly that problem. Search under my username for "non-chlorinated".
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Old 04-22-2006, 04:28 AM   #4
bugeyes
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Quote:
Originally Posted by corey_dyck
Clean the boost control solenoid, it gets gummed up and causes exactly that problem. Search under my username for "non-chlorinated".
I dont have a boost control solenoid. So it's not that.

Since posting this thread I have removed the wastegate and checked if I had a leaking diaphragm and cleaned and lubed it. Tested it on the bench with compressed air and regulator and could not fault it. Put it back on.
Took the car for a drive and datalogged it.....same problem!

Disconnected the wastegate and took the car for a spin. Regulated the boost via the accelerator and logged a perfectly smooth boost curve holding steady all the way.
I thought this would still show erratic boost if there was a leak. I do not beleive I have any leaks after this test.

Really starting to piss me off now! (even more than before)
If I can work out how I'll post a pic of my datalog. How the hell do I post a pic?
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Old 04-22-2006, 05:47 AM   #5
bugeyes
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hopefully the pic link works.
The vertical bars represent a time scale of 1 second. Target boost shoudl be 7 to 8 psi. This is a 4th gear pull.
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Old 04-22-2006, 11:08 AM   #6
JRSCCivic98
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When did this all start to happen?
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Old 04-22-2006, 07:18 PM   #7
bugeyes
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Quote:
Originally Posted by JRSCCivic98
When did this all start to happen?
When my new engine was installed with the big turbo and EWG. I havent been able to get it dyno'ed as the unstable boost is causing the ecu some problems.
So I'd have to say its always done it since being installed.
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Old 04-22-2006, 11:59 PM   #8
JRSCCivic98
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Have you considered it being a mismatched spring in the wastegate? If the spring is too weak it's possible that the fluctuations in open/close the gate might be letting out too much exhaust bypass and then closing and then again at a rate that's higher then what the turbo can push out. A GT30 is not exactly small so spool (at such a low psi within it's range) could be affected by what psi you bypass at. What kind of wastegate anyway?
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Old 04-23-2006, 03:13 AM   #9
bugeyes
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I think what is explained above is whats happenning. If it wasnt for the custom pipework I would ditch the gate I've got now and buy a new Tial or Turbosmart. The wastegate I've got now I threw out all the paperwork when I bought it and now I dont know what brand it is. Bought it about a year ago.
I'm going to look into flange sizes and see if I can get a good quality unit.
I dont think a EWC is a good idea considering the instability I have. I would rather have a stable setup and then add the controller.
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Old 04-23-2006, 10:16 AM   #10
JRSCCivic98
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You know, in all reality, if you just hook up your boost control equipment and try and tune it, it might work. If the wastegate can stay shut under power and above the 7 psi limit of the spring you might not see this issue higher in it's psi range. It's really hard to say for sure though until you try it. I've never seen a 36mm wastegate unless it's an older Deltagate. Tial makes really good ones, but the smallest is 38mm. You could always have another flange welded on or something. The pipework on the exhaust hausing/wastegate connection would also play a part in what's happening... if the design isn't right turbulance could be causing you these issues. I guess what I'm trying to say is that it's not as simple as just welding a flange on an exhaust part and hooking up a wastegate to it and calling it a day. If the flow direction is not proper the wastegate efficiency/ability will be compromised. Just a thought. Anyway, good luck with your setup. One thing to consider... try and look up some ready-made setups for GT30's on WRX if there are any... see what the major differnces are in the pipework design if your is custom made.
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