(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.

 

sorry can't get pics to copy over this is from our gm computer

but this says boost is limited to 12psi mmmm how odd

 

That's a lie, I get boost in reverse. It spikes to 5PSI

 

like boost in reverse. i have a 3000gt VR-4 which is a twin turbo V6 and slaming it in reverse is a rush. thing is fast. but soon to part with it to get a ss/sc

 

wow u really think the cobalt ss s/c is faster and better haha i would rather have the vr-4anyday!

thinturbo v6!!! or supercharged v4

I'm still gonna love my cobalt tho, but it wont be as fast as a 3000gt

 

Our cars have V4's? Hmmm didn't know that!
The VR4's had a weak transmission/axle, they don't handle power very well. Also consumers report rated them poorly.

 

Nope incorrect grasshopper. 2.0L Supercharged INline 4 not a v4

 

actually mine is a v-5

 

my friend has a colorado truck I-5 S/C. it's pretty sic
many reasons to part with a TT V6. too high maintenance. very expensive to get work done on it. to do a 60k tune up cost over $1000. too much if you ask me. besides i have a lot of ideas and connections to get the SS faster then a VR-4. i seen a SS turbo charged pushing 44lbs of boost and 535HP doing 7.4 in the quarter mile. the fastest VR-4 is a 9.6. and thats after spending about 10K-20K or more. it takes a lot to push them. and they only push 835 almost 900hp. i think waste of money if you ask me. too heavy and too high maintenance. a SS is cheaper and lighter and can be way faster. then any VR-4

 

ive driven a VR-4 man those things are ******* sick, jesus soooo much power.

 

A 535WHP cobalt running 7's in the 1/4 mile? ROTFLOL holy ****. That's enough power for a solid low 11 or mid to high 10 second pass, not no 7 second pass. omg, sorry, funniest post ever. Take into account the car is FWD, compared to AWD, so traction is going to be a bish. Right now my srt-4 is being brought up to about 650fwhp out at AMS in Illinois, and We're looking into how we can flare the fenders on the front so that I can fit a 28" slick on it since a 26" isn't even enough

 

Some just has to correct the V-4... Its not like he needs to be corrected its just a typo

 

And the are HEAVY ...the second generation had a change in trans to a getrag system however I dont think it helped with reliability ...last I checked there were 2 trans shops that were selling rebuilt VR4 trannies but one of them has since stoped

 

phase 5 cobalt (535 hp) did high 11's on 22 psi

 

you my friend.......are a PutZ

 

must be a heavy car, what do you guys normally tip the scales at? I went 11.372 @ 127.1 with about 475whp or so I'd guess (20psi of boost on stock turbo and 150 shot of nitrous)