ArmitageGVR4

iTrader: (13)

I was testing out an open element air filter setup and had my BOV vented to atmosphere for an afternoon. I noticed when it triggers, it's not a crisp stacatto blowoff but more lazy and drawn out, taking upwards of 2 seconds to finish. Is this normal behavior for an OEM valve or is mine not opening fully? Maybe it's gummed up from oil blowby or something?

dgeesaman

iTrader: (7)

If it's the ABV (BOV controlled by the line coming direct from the UIM), then yes I'd suspect that.

If it's the CRV (controlled by a solenoid), it could be the valve or also the solenoid sticking.

You can switch the ABV and CRV for a test run. It would be rather unusual that both are having a problem.

Dave

ArmitageGVR4

iTrader: (13)

Well, the problem was noticable when transitioning to off-throttle when under boost only, so I suspect it's the traditional BOV hooked to the UIM. I don't know what the CRV does -- does it fire at the same time as the ABV or under different circumstances?

Will a lazy BOV response cause noticable wear on the turbos due to backpressure against the turbine? I've got some degree of shaft play on both turbos already (75k miles original) which seems excessive for the milage but maybe not with these turbos. Coincidence? I had 130k on my old DSM turbo before I upgraded it and it had no noticable shaft play.

dgeesaman

iTrader: (7)

Turbo life depends on luck and how often the prior owners changed the oil during its life.

Yes, coming off boost is when the regular BOV (the Air Bypass Valve) is active. The vacuum created in the manifold (remember, the throttle is nearly closed, blocking the boost from the engine) activates the ABV to vent air. It should be nearly instant - at least as fast as it takes your boost gauge to indicate a few inHg - and usually it's much more vacuum than that.

The CRV operates to circulate prespool air. It is only active from 3500-4500 I believe, when the secondary is prespooling, the air goes thru the CRV instead of into the intake. That one is controlled by a solenoid which gets vacuum from the vacuum tank.

If you switch the ABV and CRV, and you notice a difference, then one of the valves isn't working. (The parts only differ slightly in their operating points - so they are interchangeable for testing). I'd guess a lazy valve in the CRV position would cause for a cruddy 4500rpm transition since it might not open in time for proper prespool, or it might not close in time at 4500rpm and prevent some boost from reaching the engine.

You can get good used CRVs and ABVs on the buy/sell forum for very cheap.

Dave