1999-2009 [Subscribe to Daily Digest] |
I have read that there are one way check valves that are inline with the top hose on the BPC that fail and are part of the EVAP system and don't allow boost to build. My 2001 Aero is stock but I have unplugged the top hose on the BPC and plugged it with a bolt. I hit the beggining of the red and when all the planets are in alignment and temperature is right it just boosts slightly into the red. I copied an explanation of what is apparently happening from another forum. Here it is:
Alright, so as you can see I've circled the check valves that fail. These one-way valves make it so that the vacuum from the throttlebody at lower power levels pulling air from the intake cobra. It also keeps pressurized air from the throttle body from escaping and going back before the turbo since the cobra is at negative pressure from the turbo sucking in air at a rapid rate at high power scenarios. Having the check valves set-up the way they are allows the EVAP system to purge when the engine is vacuuming or boosting.
Anyway, what happens is when the top check valve fails, it allows the charged air from the throttle body (when turbo is boosting) to flow the wrong way through the EVAP purge system's tubes. This pressure flows down through the lower check valve (doesn't matter whether it's good or bad) and runs into the intake cobra and to our boost control valve through that "T." That pressure then pushes open a switch inside the BCV that is meant to resist vacuum (or pressure from inside the BCV) and is controlled by the ECU. After that pressure runs into our BCV and out through the wastegate nipple (combining with another charged air vacuum line which is the bottom nipple) and causes the wastegate to open prematurely.
When the wastegate opens, exhaust gasses bypass the hot-side turbine inside the turbo and in return, the turbo slows down. Because it is opened prematurely, the turbo never has a chance to create full boost, and the turbo gauge reflects that.
My guess is that the reason the top one-way valve fails is because it is under a lot of pressure under WOT, and then straight to vacuum when off the throttle. This is constantly happening even in normal driving conditions. The bottom one-way valve probably lasts much longer because it never sees nearly the same amount of pressure either way.
It is perfectly okay to run the car without replacing that top check valve as the purge system will still operate correctly with one correctly operating valve. However, there is probably minimal performance loss as the pressure inside the throttle body will always be bleeding back into the intake cobra. However, on a stock tune the turbo will be able to compensate for the minor loss. People with aftermarket tunes may like to replace the valves because as we all know, any little bit of boost helps in the higher RPMs when the TD-04 can't hold 21 psi.
posted by 199.94.169...
No Site Registration is Required to Post - Site Membership is optional (Member Features List), but helps to keep the site online
for all Saabers. If the site helps you, please consider helping the site by becoming a member.
 |
 |
 |
 |
 |
