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

I cant let my boss see me on the puter.........gimme till tonight and I'll post again......

Ok.....the best way to test the BBS without a Tech II or a Snap-on scanner (they support GM output controls) is with a test light.

Unplug the BBS.

Turn the Ignition on.

Probe from the Pink wire (IGN voltage) to ground. The test light should light up. If it doesn't, we know where to look.....

Given we have IGN voltage, hook the test light between the two wires at the connector (Pink wire is IGN voltage, Gray is PCM ground or control).

Start the car. The test light should light up. If it doesn't, try putting the car in reverse (I know for a fact that the BBS is actuated in reverse). If/when it lights up, put the car in Drive.....it should go out. Repeat this a few times just to triple check it.

If the test light is going on and off, the circuit is probably ok, unless we need to check for actual voltage and current, which you can do with a DVOM.

BTW, The OXY SENS FUSE (20A), which is what fuses the IGN feed is in the I/P fuse panel.

Lemme know.......

Scott, thank you so much for the help. I rechecked the fuse. This time visually and it was shot. No o2 sensor or bcs. Got a new fuse in and im back at 14psi.
If i am still getting the evap codes i will replace the sol but for now im just really happy to have my 100+hp back

Cool sh*t. I'd be lost without the HP too

Great dialog in this thread, this will be very helpful if & when this happens to the rest of us. Great info Scott!

dreww wrote:

turtleman wrote:

Sure way to check the BBV, physically brace it shut (down) at the flat swinging lever with a block of wood or something. If it makes boost at that point, the BBV or something that controls it is malfuntioning. If you don't get your boost, then the vac leak must be pretty bad or theres another problem entirely

well my new BBV didn't fix the problem though it did need replacing as its been broke since I got the car. Now Im getting 2psi at WOT so its looking more like the BCS.

I think I finally figured out how to bypass it. And will check the ohms on it to to see if its functioning or not.

Did you get your boost issue resolved? I am getting 1psi at WOT.... I am going out now to check the BBV and the solenoid and all the tubes for leaks. I NEED MY BOOST AND I NEED IT NOW!

It is always so humbling looking under the hood. I have no idea what I am even looking for.
Is this the usual culprit when our cars have no boost? Is this the BBV?

Updates people, updates!

John, did you ever find the resolution to your boost troubles?

I was just driving home from mom's house and I wanted to see when I enter boost how much psi I was pulling. I think this was a bad idea but I have her WOT and was maxing at 1.5PSI! WTF!?
and then.. in the corner of my left eye I see the yellow light come on! SES! yikes!

I am getting code p1404:
EGR valve closer position performance conditions.
P1404 Exhaust Gas Recirculation System Valve 2 - Read Our Article on EGR Valve Codes For Help With This GM Check Engine Light Code

Is this just a bad coincidence or does this have something to do with my boost issue?

The EGR code that was set means that the PCM doesn't think that the pintle valve is closing properly for at least several consecutive ignition cycles, either due to carbon deposits or a bad electrical connection. One of the things the computer will do when this happens is disable the EGR, which in turn is going to increase detonation, or knock. Naturally the system would retard the spark in this case, but I doubt that it would blow off the boost as well.

Eldo wrote:

The EGR code that was set means that the PCM doesn't think that the pintle valve is closing properly for at least several consecutive ignition cycles, either due to carbon deposits or a bad electrical connection. One of the things the computer will do when this happens is disable the EGR, which in turn is going to increase detonation, or knock. Naturally the system would retard the spark in this case, but I doubt that it would blow off the boost as well.

suggest removing the EGR and cleaning it and the gas passages; consider installing a screen (available as a gasket with stainless screen in it) when putting it back on. EGRs wear out and if yours is original it may be toast. Consider getting a new BWD valve and be sure you open the box & look at it to make sure it's new and not returned. Inspect the wiring to the EGR while you're at it although I doubt it's an issue unless you been monkeying around under the hood in that vicinity. As for the lack of boost your vac lines look new but one problem can be that GM used parts outta the bin for putting this emission system together, and if you use hose that is too big gauge it will fit on some fittings and be a bit loose on others. You may have to go one or 2 sizes smaller on the replacement vac hoses to get them to seal right on the nipples. The hoses should fit TIGHT on the nipples, any that are fairly easy to put on, well, there is a good chance they are leaking new.

Thanks for the replies, guys. Any chance a bad/clogged cat would throw a SES p1404?
That would make sense for the SES and the 0 boost, wouldn't it?



---EDIT
I have been researching nonstop. Looks like a vacuum leak can also throw the p1404 SES error.

from another forum...

Quote :

Check for vac leaks. Sometimes you can get odd errors with a vac leak.

That would explain the low boost and the SES light...............right?

charlieRobinson wrote:

Thanks for the replies, guys. Any chance a bad/clogged cat would throw a SES p1404?
That would make sense for the SES and the 0 boost, wouldn't it?

0 boost would have nothing to do with a clogged cat. If anything you would have excessive boost because the air couldn't get out. Your "No Boost" situation only means that your Boost Bypass Valve is not closing. It's stuck in bypass all the time.

The BBV does use vacuum to operate, so a vacuum leak is very likely to be discovered.

so I can narrow it down to it being a great chance the problem is a vacuum leak or a BBV stuck in the open position? I am going to get to the end of this!!! I WILL SOLVE THIS AND POST MY SUCCESS! MARK MY VERY WORDS!!!

How can I be sure it is my BBV? How do I know if it is stuck open? Will I be able to move it with my fingers? Any signs to look for?

charlieRobinson wrote:

so I can narrow it down to it being a great chance the problem is a vacuum leak or a BBV stuck in the open position? I am going to get to the end of this!!! I WILL SOLVE THIS AND POST MY SUCCESS! MARK MY VERY WORDS!!!

How can I be sure it is my BBV? How do I know if it is stuck open? Will I be able to move it with my fingers? Any signs to look for?

You can see the rod move up and down on the BBV when you have the engine running and you rev the engine. The little arm should swing down when you rev it and be verticle when the engine is idleing. I am sure there is another way to test it, so hopefully someone will chime in.

- Yes, with the motor off one should be able to check the BBV actuator with his fingers. It should move freely AND be spring loaded in one direction. If the internal spring were broken, it would not close the bypass butterfly valve.

- A vacuum leak on either side of the BBV would only allow more boost - it is the TB vacuum into the top port that holds the valve into bypass mode, and the BCS allows boost to be reduced by allowing manifold pressure to be applied to the bottom port and push the diaphragm in the same direction that the TV vacuum pulls it.

- Short of the computer mistakenly commanding the BCS off, I think the likeliest candidates are a dead (and therefore open) BCS valve, or an internally damaged BBV vacuum pot.

Charlie, I cleared up a couple things in my posts on page 5, and I'd suggest reading the top half of that page to help clarify the functioning of these 3 circuits (TB vacuum, control backpressure, and electrical): https://rivperformance.editboard.com/t2083p60-faq-boost-bypass-valve-boost-control-solenoid-questions-no-boost#88568

I just thought of the most basic thing that might have been overlooked: Make sure your hoses are routed properly... From what I can see in Charlie's photo things look okay, but here's a typical Series II boost control diagram:



1 = Boost Bypass Valve Actuator
3 = Boost Control Solenoid
4&5 = Supercharger
7 = Boost Bypass Valve
8&11 = Throttle Body

98riv wrote:

charlieRobinson wrote:

so I can narrow it down to it being a great chance the problem is a vacuum leak or a BBV stuck in the open position? I am going to get to the end of this!!! I WILL SOLVE THIS AND POST MY SUCCESS! MARK MY VERY WORDS!!!

How can I be sure it is my BBV? How do I know if it is stuck open? Will I be able to move it with my fingers? Any signs to look for?

You can see the rod move up and down on the BBV when you have the engine running and you rev the engine. The little arm should swing down when you rev it and be verticle when the engine is idleing. I am sure there is another way to test it, so hopefully someone will chime in.

It was definitely moving when I revved the engine. If you look at the picture I posted above at the tubing coming from the vacuum(it says 50psi) those are definitely a shoddy job someone already did to the RIv. I was going to replace the hose with new but when I tried to take that hose off I ended up taking the nipple on the BCA with me! I think I read someone else doing this as well. I dont want to ghetto glue (jb weld) it back on so I am going to look for a new BCA If the new part and the new tube does the trick I will be satisfied. GOTTA HAVE MA BOOST!


I have been confused! I keep saying the problem is the solenoid but I just saw a picture and, in fact, it is the boost control actuator that is the problem now! The yellow circle!





http://www.3800supercharger.net/diagnosing.html
A good resource for those whose destinies bring them here


Is it ok to drive with the vaccum hose detached from the BCA? I assume it is no better or wose than whatever has been stealing my boost so far.. I am now going to blow my engine up because the vacuum line is not attached to my BCA... am I?

Does anyone know a place to get one cheaper than $40?

p.s. I know nothing about cars. ....But I want to

try moradpartscompany.com for a good used one.

But before you buy a used one, put a vacuum pump on yours and actuate it manually, just to see if it works. The vacuum lines and the little rubber ends and Ts are very sensitive and crack frequently.

it was working. but when I took the vac hose off I took the nipple with me :/

LOL, that happened to me too

BUT, i was able too "glue it back" with epoxy 5 min epoxy and it has work PERFECTLY! It's even more firmly than ever, and I applied a lil bit more on the other side (Vacuum port to the TB) to make it stronger.... and it has WORKED

Charlie, from what I've seen, $40 for a new one is good, as long as it is indeed the M90 model that fits your hoses & mounting bolts correctly. BTW, just to try to keep these darn terms straight, his part is called either the BBV actuator or BVA, Boost Valve Actuator. 'Control' is only used with regard to the BCS, the electrical Boost Control Solenoid.

As far as driving without the hose connected to the broken BVA, you are correct - it can't be any worse than it is already...
Be sure, though, to plug the hose with something so you don't add a big ol' vacuum leak.

ok, so please help me understand this even better. when the car is running WITH boost the vacuum increases pulling the rod up on the BBV which closes the hatch in the super charger's body so no air can escape and creates boost.

when the car is running with no boost the vacuum isnt strong enough to pull the rod on the BBV up so the hatch in the super charger remains open so air can escape and recycle.

Do i understand the function of the BBV accurately? Or am I way off?

boost on = rod up/spring compressed. boost off = rod down, default position spring uncompressed

You've got the basic functioning correct, you just have it backwards...

Remember, Throttle Body vacuum - what would be called 'manifold vacuum' in a non-s/c engine - is produced at low-load conditions with the throttle mostly closed, when you don't need boost. As the load increases and you open the throttle, the vacuums drops.

Thus, as in the diagram on the previous page, the vacuum is compressing the spring - holding the valve up in the bypass mode and recycling the air... As the vacuum drops along with your right foot, the spring overcomes the vacuum and pushes the valve closed, sending the air to the engine to make boost.

So,
-boost off = rod up/spring compressed.by throttle body vacuum.
-boost on = rod down, default position, spring uncompressed.