Subaru WRX Forum banner

Complicated boost issue

3K views 7 replies 5 participants last post by  ColoWRXer 
#1 ·
First off, as the title states this is complicated, but I'm going to be as informative as possible to help other people possibly diagnose my problem....so this may be a little long.

2005 WRX

txs TBE
PnP manifold and PnP gutted stock upipe
Cobb SF intake
walbro fuel pump
750cc injectors
CSS TMIC
EvoIII16g (PnP, coated)
AP v.2
Protune (91oct and e85)

I just finished installing and was tuned a couple days ago. I noticed 2 issues after the tune. 1) In higher gears (mostly 4th and 5th) when I let off the gas there is a fluttering noise coming from the turbo. 2) In higher gears (mostly 4th and 5th) when I roll on the gas from low rpm (2500-3000) the turbo starts to stutter when I reach full boost, but the stuttering smooths out and goes away after the engine revs another 500rpm. Sometimes the latter problem is so severe that the car actually bucks with the stuttering, and in 5th gear it won't rev any higher until I let off and then reapply gas.

I spoke with the tuner and a tech at txs and both had different ideas about the problem. My tuner thinks the stock bpv can't hold the boost in pushing (20psi) and so it is opening up prematurely and causing the stutter while under hard acceleration. He also thinks the bpv is causing the flutter during shifts, because it can't flow enough air to relieve the pressure left in the intercooler when the TB is snapped shut which is causing compressor surge.

The txs tech thinks they are 2 seperate problems. He thinks the bucking under acceleration is caused by overboosting and that the stutter is caused by boost cut happening repeatedly and very quickly. Like my tuner, he also thinks the noise while shifting is compressor surge due to the factory bpv not being sufficient.

So, my tuner discredited the txs techs first theory by saying that hitting boost cut, which he set at 22psi, would give a CEL and make the car bog badly, like it was out of gas or something. He told me to try the $0.16 mod ($0.16 BOV mod - Page 7 - NASIOC, so i did. It made the problem much worse, even though it's supposed to make the stock bpv hold more boost. After the mod I got the loud "squirrel" sound when shifting from ANY gear. So I reversed the mod and am back to where I was after the tune. My tuner suggests I get and aftermarket recirc valve that can handle more boost and is adjustable.

I just want to see if I can figure this out before I drop $200-$300 on a bpv that may or may not help.

Man that was long. Thanks for any ideas you might have.
 
See less See more
#3 ·
Does your tuner think that the BPV is broken, or just maxed out? I'm running 19 with no problems and I'm sure that others have seen numbers far north of that. A guy in that thread you posted was boasting 25 on the stock BPV without issues.

My gut would tell me to investigate a faulty BPV. If you modded it and the problem got worse, that would suggest to me that that is where to start. Get a used one off someone that just put in a BOV for cheap and see how that does.
 
#4 ·
The tuner doesn't necessarily think it's faulty. It was working fine before I did my 16g upgrade. He said that he usually sees the bpv max out at 18-20psi. Right now i'm running almost 21psi and that was during the 3rd gear pulls on the dyno, so I'm sure I boost a little more in the higher gears. But I did see that people were running a lot more boost on the stock bpv, so that's why I was skeptical. And the mod to the valve only made the compressor surge worse during shifts, not when I was accelerating. I changed it back anyway.

Thanks for the ideas, it's hard to know who to believe, the tuner or the tech (even though they're both just making educated guesses), so i'm just trying to understand the whole system better so maybe I can figure this out myself.
 
#5 ·
It's quite possible you just got a junky BPV. Did you buy your car used? I suspect the previous owner did something like leave the return hose off which longterm can cause damage.

I'd also make sure your wastegate is staying shut but that's easy enough to check when it's on the dyno. I'll assume that the tuner did his job and it's not as simple as just him forgetting to tighten the thing up.

I'd also note the hammer mod which can be effective at increasing the BPV's boost holding capabilities. Basically you dent it.
 
#8 ·
I wish it was as simple as a lame previous owner trying to turn the thing into a bov, but I bought the car new and have never messed with the bpv. Like I said, this never happened before my upgrade/tune, and I didn't mess with the bpv while I was installing anything else.

Mosc, I read about the hammer mod but didn't want to try it. Reason being, I already tried the mod that involves plugging the small hole inside the bpv and drilling a hole in the body of the bpv, which is supposed to make the bpv hold more boost. Well that made the problem way worse, and i had to plug the hole i had drilled and unplug the other one. So basically, the hammer mod is not really reversible. I'd hate to make it worse and not be able to fix it.

also, I hope like you that the tuner didn't make a stupid mistake. If it was wastegate related would I be able to see a fluttering or something in the WDC as I drive? I can moniter my accessport and see what happens to the WDC when I feel the stuttering.

thanks
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top