Do the FSM's have an official description of how the boost bypass solenoid and actuator work???
I'd like to know 'for real' how the solenoid works, it has three nipples, 2 of which have vacuum lines, the third is an open nipple with a piece of foam over it.
Likewise for the actuator on the s/c.
To this day, there's seems to be plenty of speculation of how to perform a boost bypass operation.
many yank the lower line off the actuator and plug the line.
others yank the vacuum line from the solenoid that runs to the manifold and plug it.
wop clamps the whole actuator off
plus a few other variations of the above.
it's nutty, it's like everyone is making a 'best guess' or 'I know someone that did this so I'll try it too'
there must be some documentation of 'how it works' available???
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hmmmm..... found this so far.....pretty interesting....
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Boost Control System Description
FIGURE Bypass Valve Open(c)
(1) By-Pass Valve Actuator
(2) Boost Signal
(3) Boost Control Solenoid
(4) Boost Source
(5) Supercharger
(6) Intake Plenum
(7) By-Pass Valve
(8) Throttle
(9) Air Cleaner
(10) MAF Sensor
(11) Inlet Vacuum Signal
Boost Control System Operation
FIGURE Bypass Valve Closed(c)
(1) By-Pass Valve Actuator
(2) Boost Signal
(3) Boost Control Solenoid
(4) Boost Source
(5) Supercharger
(6) Intake Plenum
(7) By-Pass Valve
(8) Throttle
(9) Air Cleaner
(10) MAF Sensor
(11) Inlet Vacuum Signal
Operation
Supercharger boost pressure is regulated to prevent engine and drive train damage. When the engine is operating under high boost conditions, the powertrain control module (PCM) limits boost pressure to 83 kPa (12 psi). The PCM disables boost under the following conditions:
• When reverse gear is selected
• When the engine coolant temperature (ECT) is excessively high
• When drivetrain abuse is detected
• When the vehicle is decelerating
• If an intercooler pump failure is detected
• If the intake air temperature (IAT) sensor 2 becomes excessively high
• Under heavy load in first and second gear at engine speeds above 5,800 RPM
The PCM controls boost pressure by using the boost control solenoid. The boost control solenoid is normally an 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 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. As engine load is increased, engine vacuum is decreased, causing the spring in the bypass valve actuator to overcome the applied vacuum, closing the bypass valve and allowing the boost pressure to increase. The bypass valve starts to close when the vacuum measures 250 mm Hg (10 in Hg) and is fully closed at 90 mm Hg (3.5 in Hg). When reduced boost pressure is desired, the PCM commands the boost control solenoid to operate at a 0 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.
Results of Incorrect Operation
An open boost control solenoid control circuit, an open ignition 1 circuit, or boost control solenoid valve stuck open will cause reduced engine power, especially during wide open throttle operation.
The boost control solenoid control circuit shorted to ground, boost control solenoid valve stuck closed or a restriction in the boost source or signal hoses will cause full boost to be commanded at all times and a possible overboost condition during high engine load situations.
A restriction in the vacuum signal hose to the bypass valve actuator or a stuck closed bypass valve will cause a rough idle and reduced fuel economy.
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so based on the above diagrams, I identified the lines on the actual devices
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the typical boost bypass mod is accomplished by simulating a 'malfunction' in the boost control solenoid control circuit, this is done by plugging the boost signal hose so that vacuum cannot be applied to the actuator via the solenoid.
The boost control solenoid control circuit shorted to ground, boost control solenoid valve stuck closed or a restriction in the boost source or signal hoses will cause full boost to be commanded at all times and a possible overboost condition during high engine load situations.
here's an example pic of the boost signal line disconnected from the actuator and the line is plugged tight with a screw. This seems to be the typical boost bypass method.
alternatively, you can accomplish the same result by plugging the other end of the boost signal line instead, but you will need to use a vacuum plug on the solenoid nipple
my own preference is to remove the boost signal line completely and use vacuum plugs on both nipples because I do not care to leave the nipples open.
