Hi all, just trying to get my head round how the individual components of the turbo vacuum system operate. The image I've borrowed from another thread shows the turbo solenoids located above the transmission in early 2004-2006 models. From what I can tell, the two grey solenoids are the dump valve solenoids, one for each bank and commonly referred to as the N249? If so, what are the black vacuum switches and what is their function and how do they work together with the grey solenoids?

Looks to me like the grey solenoids have 3 pipes and 2 wires, whereas the black switches have 2 pipes and 2 wires. Does anyone have any vacuum hose and electrical wiring diagrams for these 4 components please?

I believe part numbers are as follows:
Dump Valve Solenoid (Grey): 3W0906283A (bank 2), 3W0906283B (bank 1)
Vacuum Switches (Black): 037906283C

 

The black solenoids work in conjunction with the grey n 249 solenoids. The black units release the closed throttle boost to the atmosphere.

 

Thanks 1eapplebaum. So if I understand correctly, the grey solenoid controls the bypass valve located on the turbo to recirculate boost back into the intake, and the black units release boost to the atmosphere?

What conditions dictate whether boost is vented to atmosphere or recirculate to intake?

For the black units that vent to atmosphere, where do the pipes lead to before they vent to atmosphere?

 

To be fair I deduced this based on the black solenoids having one outlet to atmosphere. When I bench tested a black solenoid it allowed air to escape out the atmospheric outlet when energized. Somehow these black solenoids work in conjunction with the grey solenoids. The closed throttle boost residual pressure has to leave the intake system (dumped) in my estimation. It’s been a while since I had a look at this system. So that was my takeaway at that time.

 

Hello. Interesting thread. I've had a closer look at the vacuum diagrams on Scuderia and looks to me like they are setup as follows:

Grey Solenoid - Bypass Valve Solenoid with 3 ports
Port 1 - vacuum line from intake manifold (expect vacuum at idle and no vacuum when under boost)
Port 2 - vacuum line from intake manifold after check-valve (always under vacuum as after check-valve and connected to vacuum reservoir, etc.)
Port 3 - line towards the bypass valve actuator on the turbo

I think this has been setup to operate the bypass actuator under intake manifold vacuum in most conditions, but has the ability to open the bypass valve even when under boost using the stored vacuum if needed e.g. overboost protection

Black Solenoid - Wastegate solenoid with 2 ports
Port 1 - vacuum line from intake manifold after check-valve (always under vacuum as after check-valve and connected to vacuum reservoir, etc.)
Port 2 - line towards wastegate actuator on turbo

I think this has been setup to operate the wastegate actuator via vacuum pulling on the diaphragm when receiving the appropriate ECU signal. With regards to the wastegate actuator, I should also say that it looks like there is a second nozzle but on the bottom of the wastegate actuator that is controlled by N75 solenoid which uses positive boost pressure to push the diaphragm. I suppose the vacuum solenoid pulls the diaphragm whereas the boost solenoid pushes the diaphragm from the other side to help.

If anyone is able to confirm my thoughts above, that would be great. Would also be interested in seeing wiring diagram if anyone can share. Thanks

 

good post!