I bought an 05' Cobalt SS a few months ago and the boost gauge has never read anything over 0lbs of boost. It will go from -10 vac up to 0 on WOT, and then return back when I let off the gas.

I've tried diagnosing the supercharger's bypass valve and it seems to be working as expected. The valve will open and close freely when throttle is applied, so I dont think thats the issue.

The car also is throwing a few codes due to me having an aftermarket downpipe and cat, (P0455, P0420, P0140) but again, I dont think thats causing it either.

Does anybody have any ideas as to what could be causing the car not to boost?

 

I did try disconnecting the hose from the bypass to the solenoid and it did not seem to have any effect on it, like I said the valve opens/closes as expected when throttle is applied. How would I check if the bypass valve plate is missing?

 

Looking at it again the vacuum does sit at -15" on idle and acts as you mentioned upon de-acceleration

 

Ill check that tomorrow. The supercharger whines like it is making boost, but the gauge never indicates that it is. The car doesnt feel nearly as fast as it should (compared to my buddies n/a Cobalt it feels almost identical)

 

It turns out that my boost gauge was not working properly.
I got a bluetooth OBD2 adapter and the torque pro app on my phone said that the car was boosting to 8psi on WOT, so im just going to replace the gauge.

Thanks for the help

 

That's what I was going to guess. If your car was making zero PSI your car would be a complete turd and should be slower than an N/A SS Cobalt.