FD Stock BOV correct operation?
 

Hi guys. I have a question about the 2 brown valves on a stock FD

I know the one towards the firewall/rear of the car is the Charge Relief Valve, and it is operating as per normal.

But the other brown valve closer to the airbox (the stock BOV) is doing some very weird things...

At idle in Park, it is sucking air inwards, into the BOV :confused: Then, if I crack the throttle open with my hand, slowly up to 2000rpm and hold it constant at 3000rpm, air is blowing out of the BOV like a hairdryer :confused: The more the throttle is opened, the greater the volume of air blows out of the BOV...

Background/how I found this out: I pulled the airbox out to cut the bottom el cheapo style and put a cool air duct out under the bumper into the airbox.
When I put the airbox back in, I left the brown plastic Charge Relief Valve and BOV unconnected to the airbox to hear what they would sound like if not plumbed into the airbox. Just for sh!ts and giggles.
To my alarm, I find the front brown plastic BOV sucking air at idle and then blowing air out of it during rpm raise, while in Park (auto gearbox). Does this sound right? Am I missing something? The car boosts and drives fine. The vacuum signal lines to the top of the BOV and CRV are connected to the right places on the intake manifold as per stock. What am I seeing here?

Thanks guys :)

replace the bov. should be able to get one cheap or free. or get an aftermarket one

Based on your description they are operating according to their design. When you hit the gas you are increasing the vacuum applied to the valve. At the same time, more exhaust is flowing into the turbocharger so air is now blowing out of it.

You don't notice this operation in a completely stock configuration because you have a recirculation hose and a stock intake system. The stock air bypass valve works differently than an aftermarket valve; its operation is described in the workshop manual.

Thanks for the clarification. I understand what you're saying.

At idle, increasing the throttle, means the vacuum increases (to the small barb on the top of the BOV) and yet the increased RPM of the engine is providing increased exhaust to spin the primary turbocharger over.

So with vacuum to the small fitting on top of the BOV, and air pressure (weak boost I guess you could call it) going into the main body of the BOV, the BOV piston will let the weak boost out.

This explains why when the BOV is blowing air out, I can put my hand over its outlet and block the air, and it isnt enough to overcome my hand holding it.

As a side note, I tried to run the car on the road with the stock BOV disconnected to the airbox (non recirculating) and it didnt like it. It popped and backfired a heap. I re-connected the BOV to the airbox (recirculating) and all was fine again, and it drives normally...

The BOV doesn't vent any boost under throttle. If there is vacuum in the manifold there is no boost. It should not be open unless the car is pulling vacuum, and then it should be sucking air in. The only time the BOV vents boost is when the throttle is closed.

Whether or not the BOV is recirculated or not should have no effect on how the vehicle runs.
The BOV is black and close to the airbox
the CRV is brown and close to the y-pipe

The CRV will vent boost from the secondary compressor before it comes online.

Well this is only going off what I have in front of me, but I've got a 10-8-10 pattern car here, unmodified and 80,000km odometer. At idle, the front BOV (black valve, closest to the airbox) is sucking air inwards into the Y pipe.

As RPM increases (during idle, no load) the valve begins to blow air out. The volume of air released, increases as the idle RPM increases.

I know how the CRV works, and its the rear valve, closer to the firewall (stems out of the Y pipe before the charge control flapper butterfly inside the Y pipe)

If the main BOV (the front valve closest to the airbox with the described operation above) is disconnected from the airbox and simply vented to atmosphere, the car coughs and backfires and runs rough.
The small vacuum signal line to the front BOV is hooked to the nipple on the UIM as per factory (IE it gets manifold signal).

I cant see anything wrong with the configuration physically, and its hooked up as per factory. To rule out the plastic BOV, I pulled another one off a known stock FD which runs fine, and hooked it up to my car in place of my plastic BOV. It exhibited exactly the same behaviour- sucking air during idle, and blowing air during raised RPM in Park.
It doesnt sound right at all, but the car boosts 10-8-10 and drives perfectly when all is plumbed as per factory. Even with the BOV doing its weird suck/blow thing..?

I suspect that disconnecting the hose somehow confuses the secondary air or other emissions system

I was told you could replace either or .. I have a brown one but Not the black one can i just get another brown one to replace the lost black one? also .. how exactly do these things work . you said the workshop manual gives a description correct?

Stock BOV leaks at idle. That's why you shouldn't vent it without putting a breather filter on it...