The primary boost goes up to 10 psi and when the secondary kicks in the car makes a real loud hissing, airy noise. Along with no boost pressure after that.
Please help me. Thank you

 

There are tons of solenoids/actuators that control the transition, and the best thing to do it just test them one by one. http://www.autosportracetech.com/RX-...leshooting.htm has tons of good info on how everything works, and how to test it for proper operation.

Or, you can always go non-seq, it's much more fun.

 

Check your vacuum lines behind the black pressure tank, in front of the UIM.

 

can you hear which side of the engine bay the hissing noise comes from? if it's the middle, check the vacuum lines already mentioned, and if that doesn't work then you might have to take the manifold off if you have a manual transmission there should be only two bare nipples in the rat's nest. if you have an automatic there should be zero. use a vacuum diagram and be careful putting everything back on.

 

Check your vacuum hoses, and one-way vacuum chamber check valve. If that's ok, check your vacuum chamber to be sure it's holding a vacuum (20 inches Hg). The vacuum chamber may actually fill up with oil and not provide a vacuum--depending on how long your vacuum chamber 1-way check valve has been leaking oil into the vacuum chamber.