Yes, just a few posts up, #15, I linked to a post that I had made in another thread. In that linked-to post are links for how to get the bypass solenoid. There are also other posts in the other thread that have links to how to get the boost control solenoid, which DrLoch suggested may be the issue.

The boost control solenoid is on the turbocharger, and the bypass solenoid is mounted on the intake manifold.

BTW you can't just apply 12 volts to these solenoids, they are controlled via the ECM with a PWM (Pulse Width Modulated) signal. Applying a straight 12 volt signal can be enough to burn it up.

Are you sure, Doc? I know it's been the most common cause of overboost, but I can't recall anyone saying that it was the cause of their underboost.

That "source" has been linked to several times, it's someone in Moscow, Russia, that supposedly has one.

Thanks for the better explanation of the duty cycle that I mentioned before, I didn't know how to explain it. The computer is programmed (tuned?) And knows how frequently to send this pulse to the solenoid?

RJ, Removed source for Russian solenoid.
Try this one, BorgWarner EFR Boost Control Solenoid Replacement Kit ? Full Race

Also you are correct about the underboost situation, it was early and my brain wasn't in gear yet.

PWM is a very rapid pulse change usually used to control the degree of motion in a solenoid. I.E.: not open/close.

A digital way to control analog things.

Amazing, these things are controlled to such a precise degree. So that's why you need expensive equipment and training to be able to test and service some systems on newer vehicles.

So Don_Meier, we're back to checking for leaks on the lines associated with the bypass solenoid, and probably replacing the bypass solenoid(on the intake manifold).

An explanation for those interested. https://learn.sparkfun.com/tutorials...dth-modulation

I don't know whether you need a retune, but this boost solenoid has two large plastic mounting tabs versus OEM having one flat metal mounting tab. And if GM Stage 1 kit installed, this solenoid has max boost ~12-15 psi versus 20 with the original solenoid.

At least that is my experience after getting the Full Race Solenoid. Glad to have boost restored, but I want all of the boost!.

Thanks for the feedback. I don't know of anyone else who has used this particular solenoid to compare with what you are seeing.

The ECM is outputting a PWM signal to wastegate solenoid that in turn controls what the wastegate is doing. In HPT it's called duty cycle or PWM duty cycle if you will. The higher the duty cycle percentage value, the more average voltage/current being applied the the wastegate solenoid which controls the pressure being applied to the wastegate actuator which in turn controls what you see in terms of boost.

Read this; Boost Control Systems Explained?.. Part 1 » PERRIN Performance Official Blog

There are 3 different boost control explanations provided.

Are you sure your wastegate actuator is still good?

With the Tech2 only test is click test. I'll have the dig into it a little further.