This covers the selection, connection and wiring of the boost control solenoid.
Boost Control Solenoid
While almost any solenoid can be used for boost control, it is recommended to use a 3 way solenoid designed for boost control.
The GM 3 way solenoid is a popular solenoid:
Solenoid GM part #1997152
Wiring connector GM part #12102747
Solenoids can either be normally open or normally closed. A normally open solenoid has the advantage of not running until boost needs to be increased, but has the disadvantage of not controlling boost at all if the solenoid or hoses fail. An ECU boost cut is recommended to prevent damage if this occurs.
Notes:
| • | It is normal for the solenoid to make a ticking or buzzing sound when active. |
| • | Stepper motor type controllers will not work. |
Connecting the Solenoid
It is recommended to use an external wastegate with two ports (on both sides of the diaphragm). This is by far the most common type of wastegate. For other configurations typically the boost control solenoid operates as a bleed valve, venting pressurized air from the wastegate to the atmosphere.
There are several different pressure sources which can used to control the wastegate:
| • | Air pressure from the turbo charger outlet. |
| • | Air pressure from the intake manifold. |
| • | Air pressure which is taken from a line running from the intake manifold to the turbo charger outlet. |
Each pressure source has advantages and disadvantages - try using a pressure source from the intake manifold first, and then experiment with other sources if the boost is not stable. Do not use the vacuum line running from the manifold flange near cylinder #3 which is connected to the fast idle thermo-valve.
| • | Connect the pressure source to the 'bottom' of the wastegate (were the pressure will act to open the wastegate). |
| • | Tee the pressure source and connect via the solenoid to the 'top' of the wastegate. |
| • | Try to place the solenoid close to the wastegate and keep the tuning reasonable short (but do not place the solenoid where it will get hot). Tubes which are around 6-18 inches long will work fine. |
Wiring the Solenoid
The solenoid has two wires, with no polarity (it does not mater which wire is used for each connection):
| • | One wire should be connected to the ECU pin B21 (which normally runs the purge control solenoid on the throttle body). |
| • | One wire should be connected to +12V switched power via a 10A fuse. |
Notes:
| • | Do not use a relay between the ECU and solenoid. |
| • | High current solenoids could damage the ECU. It is recommended to confirm that the solenoid draws the same or less current as the GM solenoid listed above. |