FAQ: Boost Bypass Valve/Boost Control Solenoid Questions (No Boost)

I've never actually stopped to feel the temp of that solenoid. I will let you know what mine is acting like.
Obviously, I would think it shouldn't be hot after the car has been off for a considerable amount of time.
If it indeed is hot to the touch hours after the car has been shut down then that indicates there is still current flowing through the solenoid. I would look at the wiring diagram to see what provides current to it before condemning the solenoid itself.
Although the solenoid should be fried if it has had constant current flowing through it continuously for a while. A solenoid is only designed to accept current long enough to hold the switch open or closed for a relatively short period of time. Still need to look at the diagram and read how that system is supposed to work.
Can't be a very difficult system to troubleshoot.

Look at what Travis has for sale in the post "workbench full of stuff to get rid of"
He has an EVAP valve. Is that what you are looking at on your car?

cool thanks rw!

robotennis61 wrote:

on the series 1 there is an electrical connection going to the boost control solenoid its the one with the strange little sponge filter that falls apart when you change out the thermostat . i dont know if the series2 is different. but it stays hot. it weird. maybe its begining to fail. ill just replace it...

You're so right about that filter! I wrecked mine changing to a 180 stat and had to chase down those crazy part numbers...

I would be worried about the wiring before I replaced the solenoid. That thing should not have power to it when the ignition is off. In a '98 for example, the PCM grounds one side of the solenoid, and the other side is connected to IGN1 Hot through the Oxygen Sensor fuse. When the key's off, the solenoid power should be off...

With a shop manual and a meter/test light, you first need to find out where the power is coming from and fix any damaged wiring, and then put a fresh solenoid in.

robotennis61 wrote:

cool thanks rw!

I believe that is the carbon canister purge valve, not the BCS valve...

Eldo wrote:

I believe that is the carbon canister purge valve, not the BCS valve...

You are correct, it's the EVAP purge valve.

Eldo wrote:

And as a reminder for everyone, the boost Bypass Valve is vacuum-operated, but the vacuum circuit itself is controlled by the Boost Control Solenoid valve.

Having said that, I would be worried about the wiring before I replaced the solenoid. That thing should not have power to it when the ignition is off. In a '98 for example, the PCM grounds one side of the solenoid, and the other side is connected to IGN1 Hot through the Oxygen Sensor fuse. When the key's off, the solenoid power should be off...

With a shop manual and a meter/test light, you first need to find out where the power is coming from and fix any damaged wiring, and then put a fresh solenoid in. PM me if you need a filter for it.

Also, with that solenoid Hot at all times, that means it is commanding 100% boost at all times and that is not good. You'll be getting KR and other problems if you don't find the reason for this to be on at all times and fix it soon.

Rickw wrote:

Also, with that solenoid Hot at all times, that means it is commanding 100% boost at all times and that is not good. You'll be getting KR and other problems if you don't find the reason for this to be on at all times and fix it soon.

Actually, unless the Series I is plumbed & wired totally differently from the Series II, the solenoid is commanded 100% almost all the time anyway in a kind of reversed logic. Besides, if the '95 PCM logic is the same, the computer commands the valve from the ground side anyway...

There are several convolutions that I had to get straight in my head to understand this system...
- First of all, the solenoid (again, this is from my Series II manual) only has two command modes, 0 and 100%. It doesn't do any variable percentage tricks like other PWM devices do.
- Second, contrary to expectations, the valve is held closed when the electrical command is ON, or 100%. and it opens when 0% power is applied. I suppose this is a fail-safe idea: If the part fails you'll never have any boost, so you'll never have overboost...
- Most important, the Boost Control Solenoid switches the "control" backpressure between the blower output and the bottom port on the Bypass Valve actuator, not the "main" vacuum from the throttle body to the top actuator port...

Under most conditions, the PCM commands the boost control solenoid to operate at a 100% duty cycle (ON), keeping the solenoid valve closed and allowing only inlet vacuum to control the position of the bypass valve. At idle, full inlet vacuum applied to the top port of the BBV actuator diaphragm counteracts spring tension to hold the bypass valve open. As engine load increases, reduced TB vacuum allows the spring tension in the actuator to close the bypass valve and allow boost pressure to increase.

When reduced boost pressure is desired by the computer (see below), the PCM commands the boost control solenoid to operate at a 0% duty cycle (OFF). This opens the solenoid valve and allows boost pressure from the intake manifold to press on the bottom side of the BBV actuator diaphragm, counteracting the spring tension and the low control vacuum in the top port and forcing the bypass valve to open and recirculate excess boost pressure back into the supercharger inlet.

The PCM "desires" the boost control solenoid to operate at a 0% duty cycle (off and open): A) during rapid deceleration, B) under very high engine load situations, and C) any time Reverse is selected.

I hope this will help other guys when they search for boost bypass.

Thanks Eldo, for looking this up and more important thinking it through.
So back to his original statement that this solenoid is hot to the touch all the time, still means he has a problem. Do you agree.
This solenoid should not receive any current when key is off or during the other events that the PCM commands it to be off.

Rickw wrote:

Thanks Eldo, for looking this up and more important thinking it through.
So back to his original statement that this solenoid is hot to the touch all the time, still means he has a problem. Do you agree.
This solenoid should not receive any current when key is off or during the other events that the PCM commands it to be off.

Quite... He has to find out where that juice is coming from when the key is off.

well it seems the problem went away. for now. i checked all the connections and nothing looks out of order. when this happened,and just before turning on the engine,i turned the key as usual and went under the hood to check the BCS with a cold engine, the fans came on! they don't come on with a cold engine ever! i couldnt figure that one out? the BCS no longer stays hot but the fans activate occasionally on start up. very strange. but thanks guys for all the info. really helps me figure out what the problem is if it comes back....

Quote :

Actually, unless the Series I is plumbed & wired totally differently from the Series II, the solenoid is commanded 100% almost all the time anyway. Besides, if the '95 PCM logic is the same, the computer commands the valve from the ground side anyway...

Are you saying the engine runs under boost (BBV closed/100%) nearly all of the time? I would have to disagree. According to scan logs, my car runs without boost about 90% of the time. Or, are you saying the BBV is closed/100%, but without the engine making boost?

Quote :

The PCM "desires" the boost control solenoid to operate at a 0% duty cycle (off and open): A) during rapid deceleration, B) under very high engine load situations, and C) any time Reverse is selected.

Under very high load situations, the PCM should desire the BBV to be closed, imo. This is when you want to build the most boost.

AA wrote:

Quote :

Actually, unless the Series I is plumbed & wired totally differently from the Series II, the solenoid is commanded 100% almost all the time anyway. Besides, if the '95 PCM logic is the same, the computer commands the valve from the ground side anyway...

Are you saying the engine runs under boost (BBV closed/100%) nearly all of the time? I would have to disagree. According to scan logs, my car runs without boost about 90% of the time. Or, are you saying the BBV is closed/100%, but without the engine making boost?

Under very high load situations, the PCM should desire the BBV to be closed, imo. This is when you want to build the most boost.

As I said, you have to wrap your head around the terminology and the way the system operates... Please reread my post more carefully, especially regarding the names of the valves and their individual functions. The Boost Control Solenoid valve only has two commands, 0% and 100%, it is not variable. Also, it only controls overboost, or undesired boost.

In your post you are confusing the BBV with the BCS... In normal operation (I.e. most of the time) the Bypass Valve actuator is simply running on normal inlet vacuum, controlling the bypass valve in relation to engine load: The more gas you give it, the lower the throttle body vacuum, the more the actuator spring closes the bypass valve to give you your desired boost. There is no feedback to the computer for this, no 'percentage'.

The Boost Control Solenoid stays closed (100% on) all this time. Specifically on Reverse, decel, or very high load, it opens (0%) so that the pressure from the intake manifold can push back against the other side of the Bypass Valve actuator diaphragm and open the bypass/lower the boost... Obviously, in the first 2 of those 3 scenarios, it is more of a precaution than anything. "Very high load" should be interpreted to be "overload", and therefore something that the computer is trying to protect against, no matter how much boost the driver wants...

I suppose the simplest summary, when all the non-intuitive steps are taken to their actual conclusion, is that an open BCS means an open BBV, and that 0% BCS should mean 0% boost. BUT, a 100% closed BCS only means a possible 100% boost, if all other factors are in place, like WOT...

See, I said it was convoluted

It's hard to understand... Let me try.

The 'suction' opening of the supercharger is always accessing air, and compressing it. The bypass valve generally stays OPEN to 'bypass', allowing the compressed air to escape from the lower intake back to the front of the supercharger, to be sucked in and compressed again. A little is fed into the engine as it's running, the rest escapes back to the front of the supercharger. So the bypass valve, when it is 'bypassing', is letting the compressed air back out.

As you step on the throttle harder, you go into 'boost' mode, the bypass valve closes, forcing the compressed air to stay in the lower intake manifold under pressure, with nowhere to escape but into the cylinders.

Mark, I think I understand now. Btw, I did read every word you wrote - about 5 times over. The part that threw me off was this: "And as a reminder for everyone, the boost Bypass Valve is vacuum-operated, but the vacuum circuit itself is controlled by the Boost Control Solenoid valve."

This statement led me to believe the BBV and BCS behave similarly or identically. I never read "overboost" until your last post (that might have helped clarify). But thanks for all the info.

AA wrote:

Mark, I think I understand now. Btw, I did read every word you wrote - about 5 times over. The part that threw me off was this: "And as a reminder for everyone, the boost Bypass Valve is vacuum-operated, but the vacuum circuit itself is controlled by the Boost Control Solenoid valve."

This statement led me to believe the BBV and BCS behave similarly or identically. I never read "overboost" until your last post (that might have helped clarify). But thanks for all the info.

Sorry about that, Aaron. You're right, that earlier post wasn't clear...

When I suggested re-reading, I should've specified that I was referring to my "long" post, with the green stripe, that said: "Most important, the Boost Control Solenoid switches the "control" backpressure between the blower output and the bottom of the Bypass Valve actuator, not the main vacuum from the throttle body to the top of the BV actuator..."

Not a prob - it's complicated stuff to absorb (for me anyway). The important part is, it's written here for anyone who wants to read into it and learn - and hopefully, perhaps with your help, we can understand better!

My GTP has a little crappy LED boost guage. Still better than the Riv i guess, but at full acceleration it was only reading halfway, and the car felt sluggish. My Riv's valve stuck once a while ago and ran lousy so i checked the valve linkage first. It was fine. I'm then thinking i have a vacuum issue, but a quick test showed it's fine. So i suspect it's the vaccuum switch that feeds the bottom of the vacuum "ball", or the "ball" itself. To test this i unhooked both vacuum lines from the ball and let the linkage fall down to the intake, (bypass closed).

It idles great, maybe even better, and i have full boost on the guage with just a tap of the pedal. Plus, it a tire smoking good time. I left work with the mileage computer (another feature of the GTP) reading 16.8 average. I beat it up driving home to see how it was going to run, and have fun with it, and was reading 17.0 when i arrived 12 miles later. I can feel a little loss in torque in the mid range but it feels much more powerfull and responsive as a whole.

My question is, is it the switch, or the "ball" Or, what i mean is, whats more common of a part to fail. I'm guessing the ball because it's a moving part with vacuum on both sides of the diaphram, but just a theory. I could take the parts off my riv to test i guess, but i'd rather not touch the Riv.

What, if any, is the downside to leaving the bypass closed? I can say right now, 12 miles in, i LOVE IT.

BTW, this GTP is a $500 winter rat, that i'm on winter #2 with and including maintenace , repairs, even DMV and tax still have'nt broke into four digits yet. All i really want in the end is whatever drivetrain parts that are left for the Riv. The blower is still tight at 163k. I do wish the Riv had HUD though. It's addicting.

Ball-part #524 in the top end breakdown (sticky)
switch-part #546 " "

Vista Cruiser wrote:

I do wish the Riv had HUD though. It's addicting.

"

Sorry I can't help you with the real question, but just wanted to let you know if you look around online you can find aftermarket heads up display units that tell you just about everything the built in one on the GTP does. I have one in my Riv and I actually like it better than the one in a friends Grand Prix GXP V8 edition.

I assume by 'ball', you mean the bypass valve actuator...
That's easy to test, just pull the other end of the vacuum line off at the throttle body and suck!

yeah..but dont swallow the balls!

Eldo wrote:

I assume by 'ball', you mean the bypass valve actuator...
That's easy to test, just pull the other end of the vacuum line off at the throttle body and suck!

Yes, and Yes, it moves, but i don't think it's moving enough. Maybe if i held a vacuum on it, then see if it backs off (leaks). The more i think about it though, i want to leave the bypass closed, and have a tire shreading winter. I'll just think of it as a test and a learning curve for the Riv. In the Spring i'd be happy to walk away from it with the blower under my arm.

I hate this GTP. I feel like i'm driving some bimbo's car. I was never going to drive it again after last winter, and gave it to my daughters to drive around out in the woods. So all summer they had a blast cranking tunes and beating the shit out of it. The exaust was shot and i was'nt spending $700 on an exaust for a $500 car. But then i got a free exaust from Impala LTZ 3.9. So i thought, one more winter? What the hell. The only effects from the woods was a wheel bearing, i packed and painted the fist size rot hole under the gas door, and it looks like brand new. Now if someone would be nice enough to slide into it, i'll get full value. In reality it's so rusty, it's ready to break in half. Good thing it has the big GTP rocker covers on it. They cover up all that air behind them.

There are some things about the GTP that really sucks that Buick did'nt offer though:
1-hidden antenna
2- HUD
3-mileage computer/boost gauge
4-performace trans switch

I know, i'm just pissn' in the wind.

MY GOD MAN! YOU ARE OBSESED WITH VACUM! CHIN UP MAN CHIN UP!

Unless the spring in the actuator is extremely stiff, you should be able to suck it to the end of its travel, then hold your tongue over the end of the hose to see if it bleeds down...

If you want to beat on it, the boost control solenoid should still back it off if reach overboost, as long as you leave the other hose connected to the actuator.

1- Mast antennae usually work better than glass mount ones. But the others are cheaper...

2- I've never tried a HUD, but the option would have been nice.

3- TOTALLY!!!

4- That's what the floor-shift is for

Kyle, more info on aftermarket HUDs please! A quick google search revealed... not much. Maybe I'm just searching the wrong terms.