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

Hi guys, so I was experimenting something, and I am running about 3 psi of boost, then if I unplug the vacuum line from the bypass actuator to the bypass solenoid, I get 7psi, is my boost solenoid going out?

Yes. Replace it.

Ok sweet, that's the last thing then, thanks

What are you guys considering the bypass "solenoid" ? isn't it just a mechanical vacuum actuated system?

96_Juggernaut wrote:

What are you guys considering the bypass "solenoid" ? isn't it just a mechanical vacuum actuated system?

Yes and no. It's actually an ON/OFF that's PCM controlled. Ever notice the 2 wire plug that connects to it? The PCM commands it ON/OFF based on Reverse/Drive. The vacuum side of it controls Boost Ramp Rate and what-not. If it's electrically shorted "open", you'll get very little boost from the vacuum control of it.

(though you can make it only vaccum controlled if you bypass it like the image I linked. it will still function and bypass as normal. the only thing it won't do is briefly drop boost at shifts for transmission protection. The drop is only a fraction of a second, but aparently makes a difference. also the whold boosting in reverse thing. having the proper thing in there is the best thing, this was just an FYI.)

I'm not sure which one is which in this scenario. I believe the BBV is the part with the enclosed diaphragm and the arm that comes out the bottom that goes up and down depending on throttle. Anyway, what is the normal operation of this diaphragm/arm? With the car parked and idling (95 Riv), when I give it a very large amount of throttle, the arm will come down but immediately go back up. Isn't it supposed to stay down? Also, I've listened to youtube videos of these cars running and they have a very loud tell tale whine which I don't really hear on mine. Am I not making boost? I just replaced the coupler and oil in mine, and used a new SC gasket and whatnot. All vacuumm lines are intact and I replaced the questionable ones, and they are all hooked up properly. Any help would be appreciated...

And yes my CEL is on, I'm actually getting those checked out tomorrow since I have to drive to a shop that can do OBD 1.5. I just wouldn't think an electrical issue would cause my car to "sound" like there is no boost unless the BCS is truly dead...

billfrank85 wrote:

when I give it a very large amount of throttle, the arm will come down but immediately go back up.

That is normal. When you give it throttle really fast, it initially plunges down (closing the boost bypass valve) but then when rpm and vacuum reach a regulated state again just a moment after you push the throttle down, it'll go back up because there's no load on the engine to let you get far into throttle without just over-reving. So you won't get it to stay down in boost mode unless you have load on the engine and can hold some real throttle basically.

I originally replaced my boost control solenoid with a working used unit from a junk yard. That one is now reading zero ohms and I am looking for a new one. I don't see any for the 95 riv, but can the bracket be used from the 95 bcs to make a 96+ bcs work?

I posted this question awhile ago, but does anyone know if a series 2 boost control solenoid can be fitted to the series 1 using the old bracket? I cannot find a boost control solenoid for the series 1 anywhere.