BoV question.

That spinning thing that makes all of the cool noises. OE and Aftermarket.

Moderators: Helpinators, Moderators

Post Reply
Pythonmsh
First Gear
Posts: 59
Joined: Mon Jul 22, 2013 4:55 am

BoV question.

Post by Pythonmsh »

When the car is cold the car will act like it's going to die when shifting then jump right back up. It's fairly random and doesn't do it when it warms up. But it's only after boosting and I shift or clutch in. (First 5-10min) and doesn't always do it. If it does start acting up it does it maybe once or twice then stops after its warmed up a little.

My current mods are
td04 set to 12-13 lbs with Hallman HBC
TMIC
Full turbo back exhaust
The coffee can intake mod that I found on these forums. Using a cone filter though.

and I got a free BOV from a buddy. My old BPV setup with was a bit jerry rigged and the hose into the TMIC was pretty much held together with a fitting and RTV, it worked fine until the top mount gets taken off and on then it started to get weak and leak.

It doesn't seem like the BOV leaks at all. No flutters or anything like that or weird sounds under boosting.

I currently have a Vacuum of 22-23 and it holds boost 12-13 just fine. I'm just wondering if this is something I should truly be worried about.

Edit - Also no check engine lights.
Alphius
Fourth Gear
Posts: 1204
Joined: Mon Aug 31, 2009 9:09 pm
Location: Rochester, WA

Re: BoV question.

Post by Alphius »

The BOV vents air that has already been metered by the MAF, therefore causing a massive rich spike when you shift due to the ECU still injecting the fuel for that air that is no longer a part of combustion.

On a MAF car you really should have a bypass valve back into the intake.
Pythonmsh
First Gear
Posts: 59
Joined: Mon Jul 22, 2013 4:55 am

Re: BoV question.

Post by Pythonmsh »

Alphius wrote:The BOV vents air that has already been metered by the MAF, therefore causing a massive rich spike when you shift due to the ECU still injecting the fuel for that air that is no longer a part of combustion.

On a MAF car you really should have a bypass valve back into the intake.
How come it doesn't do it when the car is warmed up?
James614
Fourth Gear
Posts: 1744
Joined: Sun Jun 10, 2007 4:35 am
Location: Arkansas

Re: BoV question.

Post by James614 »

When its cold the engine is in open-loop, the fueling is preset and it isn't using the MAP sensor or O2 sensor to adjust to an AFR target yet. Once warm its using more sensors to operate, so it may be able to save itself from stumbling and choking when its warm. But you still want to get a BPV on there as the BOV can increase turbo lag and reduce initial torque after the shift (I've seen this data logged on WRXs, the ECU goes nuts every time the BOV opens).
93 Touring Wagon (EJ20G 5spd Swap) -- Finally back and running strong as ever!

05 Outback 2.5XT 5spd -- Now the wife can have her SUV and get in on the turbo Legacy goodness at the same time.
Pythonmsh
First Gear
Posts: 59
Joined: Mon Jul 22, 2013 4:55 am

Re: BoV question.

Post by Pythonmsh »

James614 wrote:When its cold the engine is in open-loop, the fueling is preset and it isn't using the MAP sensor or O2 sensor to adjust to an AFR target yet. Once warm its using more sensors to operate, so it may be able to save itself from stumbling and choking when its warm. But you still want to get a BPV on there as the BOV can increase turbo lag and reduce initial torque after the shift (I've seen this data logged on WRXs, the ECU goes nuts every time the BOV opens).

One of the local big subaru shops told me it's probably due to overboosting in the colder weather while it's warming up.

I did have it set to 12-13lbs and I feel like it was overboosting a little bit.

He said it was due to overboost fuelcut. I'll be getting an HKS FCD from him soon for a good price.
James614
Fourth Gear
Posts: 1744
Joined: Sun Jun 10, 2007 4:35 am
Location: Arkansas

Re: BoV question.

Post by James614 »

Does it only do it at full boost when it ls cold? From what you said it sounded like it happens during normal driving, where you should be WAY below fuel cut unless your waste gate is malfunctioning.
93 Touring Wagon (EJ20G 5spd Swap) -- Finally back and running strong as ever!

05 Outback 2.5XT 5spd -- Now the wife can have her SUV and get in on the turbo Legacy goodness at the same time.
Pythonmsh
First Gear
Posts: 59
Joined: Mon Jul 22, 2013 4:55 am

Re: BoV question.

Post by Pythonmsh »

James614 wrote:Does it only do it at full boost when it ls cold? From what you said it sounded like it happens during normal driving, where you should be WAY below fuel cut unless your waste gate is malfunctioning.
It only does it when the car is cold yea. It's perfect when it's warmed up.
James614
Fourth Gear
Posts: 1744
Joined: Sun Jun 10, 2007 4:35 am
Location: Arkansas

Re: BoV question.

Post by James614 »

But I mean does it only do it at or near full boost shifts?
93 Touring Wagon (EJ20G 5spd Swap) -- Finally back and running strong as ever!

05 Outback 2.5XT 5spd -- Now the wife can have her SUV and get in on the turbo Legacy goodness at the same time.
Pythonmsh
First Gear
Posts: 59
Joined: Mon Jul 22, 2013 4:55 am

Re: BoV question.

Post by Pythonmsh »

James614 wrote:But I mean does it only do it at or near full boost shifts?
Yea.
Alphius
Fourth Gear
Posts: 1204
Joined: Mon Aug 31, 2009 9:09 pm
Location: Rochester, WA

Re: BoV question.

Post by Alphius »

Here's the problem with the "Subaru shop's" theory: In these cars overboost fuel cut occurs after 3 seconds above 13psi, and as soon as manifold pressure drops below 13psi fuel returns. The car would never die on clutch in from this process because the fuel returns as soon as the throttle plate closes. In addition, the fuel cut is a very harsh feeling. You would know if it was happening at any time.

I can guarantee it is because of your BOV venting metered air. The reason it only happens when the car is cold is simple. A cold combustion chamber is easier to flood from too much fuel than a hot combustion chamber. So when the car is cold, the extra shot of fuel is causing it to stall out during shifts. When the car is warm, it just burns the extra fuel.

If you can live with the issues you can keep the BOV. It's not great for fuel mileage and you should probably change your oil every couple thousand miles due to fuel contamination but it really won't hurt anything to run extra rich every time the BOV opens. Like James614 said though, if you're wanting a little better performance and you can live without the sound of a BOV, you should really switch back to the BPV.
Pythonmsh
First Gear
Posts: 59
Joined: Mon Jul 22, 2013 4:55 am

Re: BoV question.

Post by Pythonmsh »

Alphius wrote:Here's the problem with the "Subaru shop's" theory: In these cars overboost fuel cut occurs after 3 seconds above 13psi, and as soon as manifold pressure drops below 13psi fuel returns. The car would never die on clutch in from this process because the fuel returns as soon as the throttle plate closes. In addition, the fuel cut is a very harsh feeling. You would know if it was happening at any time.

I can guarantee it is because of your BOV venting metered air. The reason it only happens when the car is cold is simple. A cold combustion chamber is easier to flood from too much fuel than a hot combustion chamber. So when the car is cold, the extra shot of fuel is causing it to stall out during shifts. When the car is warm, it just burns the extra fuel.

If you can live with the issues you can keep the BOV. It's not great for fuel mileage and you should probably change your oil every couple thousand miles due to fuel contamination but it really won't hurt anything to run extra rich every time the BOV opens. Like James614 said though, if you're wanting a little better performance and you can live without the sound of a BOV, you should really switch back to the BPV.
Right. I didn't get the BOV for the sound. I had a jenky setup with the old BPV. It was given to me for free.

When I went to take cash out from a store I tried to see if turning the boost down would do anything. It didn't.

I had the car running for about a minute and I wanted to see if it made any change. So I hit boost but it died completely and it took about 30 cranks for it to start back up while I applied the gas to keep it running. Obviously you should stay out of boost while the car is cold but I doubt the car should die even if you do so.

Maybe I need to get the adapter plate and a stock wrx BPV for the winter. Or even keep it like that in general. The BOV sound is fairly nice for a while but it's not worth these problems.
Pythonmsh
First Gear
Posts: 59
Joined: Mon Jul 22, 2013 4:55 am

Re: BoV question.

Post by Pythonmsh »

I don't know if I even need the plate. Since I have a 06 XT top mount. I didn't need any special plates or anything to mount this HKS SSQV. It's most likely a knock off but it doesn't leak and it holds boost just fine. But I can't have the car dying and have that chance of it not starting up again.

I'm assuming I can get a stock wrx BPV and bolt it right up?
Alphius
Fourth Gear
Posts: 1204
Joined: Mon Aug 31, 2009 9:09 pm
Location: Rochester, WA

Re: BoV question.

Post by Alphius »

The stock WRX BPV interferes with the throttle cables. The WRX has the throttle cable on the other side of the TB.
You need a BPV adapter plate like in this thread: http://bbs.legacycentral.org/viewtopic.php?f=3&t=38598
Pythonmsh
First Gear
Posts: 59
Joined: Mon Jul 22, 2013 4:55 am

Re: BoV question.

Post by Pythonmsh »

Alphius wrote:The stock WRX BPV interferes with the throttle cables. The WRX has the throttle cable on the other side of the TB.
You need a BPV adapter plate like in this thread: http://bbs.legacycentral.org/viewtopic.php?f=3&t=38598
You sure I'll need it?
http://cdn.iofferphoto.com/img3/item/14 ... -a5724.jpg

I can fit that thing.
Pythonmsh
First Gear
Posts: 59
Joined: Mon Jul 22, 2013 4:55 am

Re: BoV question.

Post by Pythonmsh »

Sorry for double posting.

http://i398.photobucket.com/albums/pp62 ... AG0175.jpg

http://bbs.legacycentral.org/viewtopic.php?f=9&t=46768

My top mount is the slim one like this one in the picture. It looks like this guy didn't need a plate, so I think I might be just fine.
Alphius
Fourth Gear
Posts: 1204
Joined: Mon Aug 31, 2009 9:09 pm
Location: Rochester, WA

Re: BoV question.

Post by Alphius »

I had always heard that the stock BPV fits, but the outlet of the recirc line points directly at the throttle cable so there is no way to run a hose to the intake. If there is a way, that is awesome and you should have no problems with it hooked up properly.
Pythonmsh
First Gear
Posts: 59
Joined: Mon Jul 22, 2013 4:55 am

Re: BoV question.

Post by Pythonmsh »

Alphius wrote:I had always heard that the stock BPV fits, but the outlet of the recirc line points directly at the throttle cable so there is no way to run a hose to the intake. If there is a way, that is awesome and you should have no problems with it hooked up properly.
Image

Right after taking a look it looks like I should be able to fit the stock wrx BPV and route the lines down underneath between the y pipe and the intercooler. There's about 2 inches of room and it'll route directly back into the intake.

I hope it all works out... some people seem to have luck and some people don't.
James614
Fourth Gear
Posts: 1744
Joined: Sun Jun 10, 2007 4:35 am
Location: Arkansas

Re: BoV question.

Post by James614 »

IIRC the FXT and WRX TMICs have the BPV at different angles. I think the FXT doesn't require the adapter.
93 Touring Wagon (EJ20G 5spd Swap) -- Finally back and running strong as ever!

05 Outback 2.5XT 5spd -- Now the wife can have her SUV and get in on the turbo Legacy goodness at the same time.
James614
Fourth Gear
Posts: 1744
Joined: Sun Jun 10, 2007 4:35 am
Location: Arkansas

Re: BoV question.

Post by James614 »

93 Touring Wagon (EJ20G 5spd Swap) -- Finally back and running strong as ever!

05 Outback 2.5XT 5spd -- Now the wife can have her SUV and get in on the turbo Legacy goodness at the same time.
Pythonmsh
First Gear
Posts: 59
Joined: Mon Jul 22, 2013 4:55 am

Re: BoV question.

Post by Pythonmsh »

Right. Mine has the 45 degree angle on it or what not. My recirc line will have to be routed underneath but it won't be no big deal

Hoping for the best!
Post Reply