Why do some (one port) actuators recieve both boost and vacuum
 

OK … I’ve been troubleshooting a 12-6-7, creeping to 9 boost problem since I bought my car. No questions about this … at least not yet. ;)

Today I discovered that the Charge Relieve Valve (the one that let’s the secondary turbo prespool) is leaking boost, just a bit. I’m going to order a new one tomorrow. I discovered that the valve is controlled by not only vacuum, but also boost from the secondary turbo. What’s the scoop with this? I.E. the valve is fed from a solenoid in the front of the “rat’s nest” rack. This solenoid either sends vacuum (from the vac chamber) or boost from the second turbo to the CRV. So why not just vacuum and atmospheric pressure? I imagine that this is to close the CRV rapidly, “hold” it shut, of perhaps the valve needs to see an equal pressure to what is flowing threw it. Anyone know why this is done? I noticed that the CRV isn’t the only valve / actuator to do this. Oh, I do understand the Turbo Control Actuator … this was one of my first fixes. It’s all of the other valves that have one input and vary from pressure to vacuum or visa versa.

Thanks all,

James