SC Boost Question

[Ross]

From AllDataDIY:
The bypass valve is controlled by a vacuum actuator which is connected to the vacuum signal between the throttle and the supercharger inlet. Spring force from the actuator holds the valve closed to create boost, and vacuum pulls the valve open when the throttle closes to decrease boost. The open bypass valve reduces pumping loss thereby increasing fuel efficiency.

The solenoid valve attached to the bypass actuator is an electronically controlled, 3-way valve. This valve, controlled by the powertrain control module (PCM), determines whether pressure from the manifold is routed to the bypass actuator or closed off. The valve allows pressure from the manifold to open the bypass valve and regulate boost pressure during specific driving conditions.

Supercharger boost pressure is regulated under certain conditions to prevent engine and drive train damage. When the engine is operating under high boost conditions, the powertrain control module (PCM) can limit boost pressure to 83 kPa (12 psi) or less. The PCM disables boost under the following conditions:

• When reverse gear is selected
• When the vehicle is decelerating
• If an intercooler pump failure is detected
• If the intake air temperature (IAT) sensor 2 becomes excessively high
• If the engine coolant temperature (ECT) becomes excessively high
• Under heavy load in first and second gear at engine speeds above 5,800 RPM
• When drivetrain abuse is detected

The PCM controls boost pressure by using the boost control solenoid. The boost control solenoid is a normally open valve. Under most conditions, the PCM commands the boost control solenoid to operate at a 99-100 percent duty cycle. This keeps the solenoid valve closed and allows only inlet vacuum from the supercharger plenum to the bypass valve actuator to control the position of the bypass valve. At idle, engine vacuum is applied to the upper side of the bypass valve actuator, counteracting spring tension to hold the bypass valve open. When the engine load is increased, the engine vacuum is decreased, causing the spring in the bypass valve to overcome the diminishing applied vacuum, closing the bypass valve and allowing the boost pressure to increase. When reduced boost pressure is desired, the PCM commands the boost control solenoid to operate at a 0-98 percent duty cycle. This opens the solenoid valve and allows boost pressure to enter the bypass valve actuator at the lower side to counteract the spring tension, opening the bypass valve, and recirculating excess boost pressure back into the supercharger inlet.

There is more.... but this is getting long.

 

[ctuinstra]

That I cannot say with any certainty because my S/C Ecotec experience is with a Cavalier not a Cobalt and when installing the same supercharger kit on Cavaliers you let the bottom of the bypass valve vent to atmosphere and there is no solenoid used. But it being a solenoid to limit boost seems odd to me since the M62 will not make enough power to hurt any stock Ecotec, so I don't see a need for it.

On this car, how I have it plumbed (and I am quite certain but not positive is correct), the bottom of valve is run through the solenoid and to the intake after the supercharger. With the solenoid not activated, it vents straight through. So the bottom of the valve is running straight to the MAP area. I can't wrap my head around why and what it is doing for certain. I'm also leaving out a lot of questions so as not to overwhelm others with them.

 

[ctuinstra]

From AllDataDIY:

Great information. That helps a lot. I will get on there and read more about it. That's pretty much what I figured is how it's working but how I have mine plumbed is when the solenoid is active, this open up the vacuum line to manifold to atmosphere and this would be a considered a vacuum leak!! Should the lower side of the solenoid be plugged off? I'll read more and see if it says anything in there about it.

 

[Ross]

Green is inlet vacuum.
Red is output from the solenoid
which is either Yellow (pressure from the manifold ), or Blue, which is open to atmosphere.

 

[ctuinstra]

Thanks! All good. That's how mine is plumbed. After reading some more, the solenoid is actuated 99-100% of the time! This is completely contrary to normal design. That's what was throwing me! The solenoid only closes (or deactivates) when the PCM wants to reduce boost. When this happens, the manifold is still under pressure when it vents to the open port of the solenoid and thus is not actually a vacuum leak as I thought it would be. Not a vacuum leak when it's under pressure. Kind of scary when you think about it. Forget to plug in the solenoid, you have permanent vacuum leak!

 

[ctuinstra]

I have considered temporarily adding a dash LED or 12V bulb to the solenoid.
So when the PCM decides to turn on the solenoid, the light turns on.

I finally worked on a way to use my old AEM AFR gauge to log the action of the solenoid. Since I have a bad O2 sensor, I cut the sensor off of the harness and figured out how to wire it up to a 12v signal. It's very crude but will get the job done. Basically the gauge with read either 11.0 AFR when the solenoid it off and 14.7 when it's on. Using the AEM, I can use the serial output of it to scan using HP Tuners and see exactly when it activates. Now, I haven't actually hooked it up because I kind of past that point, but just wanted to see if it could be done and it can. It could read any 12 signal, just on/off and not actual voltage.

 

[Ross]

I finally worked on a way to use my old AEM AFR gauge to log the action of the solenoid. Since I have a bad O2 sensor, I cut the sensor off of the harness and figured out how to wire it up to a 12v signal. It's very crude but will get the job done. Basically the gauge with read either 11.0 AFR when the solenoid it off and 14.7 when it's on. Using the AEM, I can use the serial output of it to scan using HP Tuners and see exactly when it activates. Now, I haven't actually hooked it up because I kind of past that point, but just wanted to see if it could be done and it can. It could read any 12 signal, just on/off and not actual voltage.

Very cool!

I want to put my oil pressure gauge on HP Tuners log files... the oil pressure gauge isn't stock, and isn't on GM low speed LAN, so it isn't available to the log files. It is on an arduino, and I have spent a bit of time looking at putting it on the GM LAN.

 

[ctuinstra]

Very cool!

I want to put my oil pressure gauge on HP Tuners log files... the oil pressure gauge isn't stock, and isn't on GM low speed LAN, so it isn't available to the log files. It is on an arduino, and I have spent a bit of time looking at putting it on the GM LAN.

Find out if you have install a library or something on the arduino to add a serial output. Then you would have it made. All you have to do is output the value and then a line return and form feed or something like that. I ran across the exact serial output of my AEM gauge and it was the value and two commands over and over.

 

[Ross]

There is a good article on it here. We are getting into Bradr's area of expertise. His product could be the hardware for a custom software interface for gauges that talk on the CAN network.