I'm having a problem where my BOV opens under boost. I can hear it fluttering, as I'm accelerating. This has plagued me for the last 2 months.

Background on the car:
97 Eagle Talon Tsi AWD
automatic
evo 8 ecu
2g DSM MAS
BOV recirculated

To fix it, I've tried:

• Boost leak test
• New BOV vacuum line (Tried both as short as can be and much longer than needed.)
• Different vacuum ports on the IM for the BOV line.
• Switched from v5.10 to v7
• Different ignition and fuel maps (stock DSM, stock Evo 8, and slightly tuned)
• Different spark plugs
• New spark plug wires
• Compression tested
• Different BOVs. First was an HKS SSQV. I just put a chinese type-s that I had laying around today.

I have my MAS and injectors dialed in so that my LTFT hover +/- 2%. Right now, they're sitting at: -0.09% and +0.89% for low and mid respective.


You can see the jumps in airflow on the graph.

So I come here asking for advice. What do I check next? Is there something in my tune that could be causing this?

 

Just wondering, but do you see any flucuation in your AFRs when this happens? Also what type of intake do you have on the car?

 

The AFRs seem to hold pretty steady during this. It flutters so fast that I don't think that any fluxuations show up on the wideband. I'll try getting a good log of that today.

I have an intake pipe I got off eBay, but there are many others running it without problems. It worked fine with the stock ECU.

The BOV runs on it's own dedicated vacuum line.

 

also would like to hear more about this ...i have the same problem

 

A BOV operates on the difference of pressure between the Intake Manifold and IC Pipes. The Throttle Plate causes this difference of pressure. This is a mechanical problem not a tuning problem.

Things that could cause fluttering:

Part Throttle Acceleration - Throttle Plate isn't opened all the way.

Turbo Surging - Engine can't keep up with Turbo.

Bad / Improperly Adjusted BOV - BOV is blowing open under boost, or it blows off with to little difference in pressure.


Your problem is most likely Improper Adjustment, crank the adjustment screw tight, or add shims. If you BOV has a second nipple, I think connecting it to the turbos boost source prevents early opening. A 1G BOV flange is close to the Greadys, you could try a Crushed or Dodge Modded 1G BOV. My Modded 1G stays closed above 25 psi.

 

My SSQV did the same thing, so I came up with a fix for it. The other valves are probably just blowing open. Check this out for the SSQV and see if it works for you...

https://www.evolutionm.net/forums/ev...sqv-users.html

I also replied in the other thread with this link too, didn't see this one at first lol.

 

The HKS SSQV I'm using is the v2 model, so no adjustment screw.
I even put my eBay Type-S back on, with 2 thick washers and the screw tightened all the way down, I still had problems.

I'm not sure I see the point of your modification, and how it works with the design of the BOV.

 

The way the SSQV operates when working properly is pressure is fed into the initial chamber, and then through the check valve the pressure also bleeds into the rear chamber to equalize both sides. When the slightest pressure variance happens (such as turbo running out of air up top) the check valve tends to stick and the valve sees a pressure difference from one side to the other and opens and then quickly closes when the pressure is normalized again. It's a wonderful design for a turbo that never drops off up top, but higher gearing places a higher load on the turbo which just can't seem to keep up, and thus the rapid opening and closing. Modding it to block off the rear chamber and allow only atmospheric pressure on the rear side essentially turns it into a standard bov with all the benefits of a positive pressure seal.

I currently run the knock-off with this mod done, and I see upwards of 28psi with a slight decline in 5th gear with no surging or premature opening, and I have tested it up to 34psi so far.

 

No problems with the knockoff SSQV then? I've been thinking about getting one because my Forge bov doesn't sit closed at idle and annoys me even though I know that it is supposed to be that way.

 

Also, did you do a vacuum line reduction? Is your BCS line on the same line as your BOV? If so, when the BCS/MBC starts to bleed air from the line, it reduces the pressure holding the valve closed (then boost drops, EBC closes again, wash, rinse, repeat).

This was initially a problem for me in 5th gear with a 35R, but is a pretty common problem in the community.

You could also be going way under/over your targets if your TBEC is set too high.

 

The MBC is on it's own line, and the BOV is on it's own line.

 

No problems even with the knock-off now. I know I'll catch flak about it being a fake, but now it seems to work better than any other valve I've ever tried...hands down. I don't remember if it sits open at idle though, I'll have to look at it and see. For me it really isn't an issue with speed density, but if a single spring type-s will idle ok, then this should be fine too.