Weird boost problem

[nate halter]

Hey guys, new to site. Lots of great info that I have already read about boost problems. Well I have a problem as well. I have an L67 in a 97 cavalier with the getrag F23 trans with it. Car runs great... could be better. I have a 3.4 pulley on it and I have done the boost bypass and am only getting 5 psi on a mechanical boost gauge. When I rev it up in neutral it goes to about 8 psi. When driving when I lean into the throttle the boost spikes to about 8 psi then immediately drops to 5 psi. Im not understanding this at all. You can see it on the recorded runs I have with HP Tuners. Have recorded numerous runs with no knock. Mods: full 2.5 exhaust, 42.5 injectors, CAI, LS6 springs. I can send you the log file if you would like to take a look. Thanks for any suggestions.

[Slick2500]

Check for vac leaks and make sure your vac lines are routed correctly.
I am going to assume you are using a 98+ blower.

[J57ltr]

Sounds like the boost valve is connected to boost bypass exhaust port (top) instead of the bypass port.

Jeff

[J57ltr]

Sounds like the boost valve is connected to boost bypass exhaust port (top) instead of the bypass port.

Jeff

did you check into this? Because if you have the bottom port of the actuator connected to the exhaust you will see exactly what you were seeing since the spring will not be able to overcome trapped air in the lower section of the actuator and it will kind of balance with the bypass partially open.

Jeff

[nate halter]

All the lines are routed correctly. Let me ask you this, Im still running the stock size supercharger belt, could it be slipping causing this? I dont hear any squealing or anything but could this be the issue im wondering?

[Scottydoggs]

what map sensor you running? maybe its bad?

[nate halter]

I completely took off the boost bypass valve and made the valve stay shut and I had full boost, so the boost solenoid must be bad. When they fail they must fail in the open state so that the boost is pushing the bypass valve open through the solenoid!

[Scottydoggs]

with the bbv all hooked up, does that lever on the bottom move when you rev the engine?

[nate halter]

The valve is open with the engine running and when I rev it, it shuts

[nate halter]

Yes I checked, the top of the boost bypass valve is connected to the top VAC port on the engine.

[J57ltr]

I'm talking about the bottom connection on the bypass actuator that connects to the solenoid.

[nate halter]

yes the bottom is connected to the solenoid.

[J57ltr]

There are 2 ports on the solenoid the upper one is exhaust and the lower is for opening the valve when called for. If you are connected to the top port it won't allow air to escape the lower portion of the bypass and it won't close all the way because the air trapped inside the actuator. Have you already replaced the solenoid and everything is good now?

Jeff

[nate halter]

The vacuum diaphragm actuator (BBV) has two ports, one on the top and one on the side. The port on the side is going to the electrical solenoid that gets commanded by the computer. The top port goes to the top of the supercharger that has manifold vac.
Looking at the solenoid from left to right the left side is connected to the same VAC/BOOST line that goes to the FPR and the right side goes to the bottom port on the BBV.