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Discussion Starter #1
I am fighting with a surging issue that I need a little advice in fixing. I have a 91T mostly stock. Mods: exhaust, A/W ic, 15lbs of boost with mbc, no egr, fcd.

This is the prob. When I am going up a hill, not hard but keeping up with traffic, I am building a little boost. I lightly let off the gas and there is this surging that goes along with the bpv flutter. Is this compressor surge? There is no vacuum leak, the afm and tps are within spec, and the bpv vtv is new and in the correct direction (black side toward drivers side). Could this be a faulty bpv?

Any advice would be a great help.

Thanks,
Brad.
 

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Usually that happens with an aftermarket BOV since it's not recirculating the air. I would double check everything on the BPV and make sure there are no leaks or anything.
 

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Discussion Starter #3
I will recheck the whole thing agian tomarow with the smoke machine. Anyone else?

Thanks,
Brad.
 

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Discussion Starter #6
OK, I have replaced my afm with a known working one. Reset TPS, and checked for boost leaks again. Checked the BPV per TIS. Installed all new vacuum lines from intake to BPV. Cleaned the throttle body.

I understand the system, and know how and why it works. This is just crazy that I cannot figure this out. Any other suggestions?

Thanks in advance,
Brad.
 

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"Surging" as in compressor surge, or "surging" as in engine output surging back and forth? Surging in general comes from AFR that's off (intake leaks, use a pressure tester) or overly-advanced ignition timing (check base timing with TE1 and E1 jumped).

This is assuming each sensor is functioning, of course.

When tuning an EMS, this can also be caused by adjacent cells not being smooth, but that's clearly not the case in your car.
 

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Discussion Starter #8
Timming is perfect @ 10 deg. I am going to use a pressure tester on Monday, but I have already used a smoke machine. Is a pressure tester that much better? All the sensors have been checked per TIS, and are within spec.

When I say "surging" yes I mean compressor surge. It only happens when I lift throttle a little bit under boost. Not full boost, but with 5 or so lbs I lift my foot a little. When the BPV flutters I get this surging that corresponds the flutter. If I lift my foot completely there is a whoosh of the BPV fully opening, but no surge.

I hope that helps,
Brad.
 

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Smoke won't work with pre-throttle body intake system, which will effect the AFM. Pressure testers in conjunction with a stethoscope is very effective!

Compressor surge on small throttle lifts like that is normal on the stock system. With partial throttle lifts, the BPV opens a little, as opposed to all the way with full throttle lifts. Take solace in the fact that the surge is likely happening at low boost pressures and likely not damaging to the turbo.

On a side note - it's exceptionally hard on the turbo to climb hills in a high gear constantly in boost, even a few psi.
 
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