Hello all.
Yesterday my 09 cobalt ss with a stock turbo all of sudden had no boost. Everything was working fine earlier in the day and before it lost boost.
I noticed the highest the boost would go was 2.5psi but it couldn't hold it. I was close to home when this happened so I just parked the car.
No cel but I was only a short distance from home.
I took the hot side charge pipes off and found no oil. I checked the intake and found no oil. Both were very dry with no residue of oil.
The turbo has ZERO shaft play. The turbo looks good I think?
I'm no expert but I think maybe the BPV is stuck open?
Any tips would be greatly appreciated.

 

Starting with low hanging fruit, add you do a boost lea test and check vacuum lines and solenoid connections.

 

What ECaulk said. I would start with looking at and feeling all vacuum lines. Then pressurizing the charge air system to find a leak. I'm sure there are DIYs to do it, but it's as simple as getting PVC pipe caps and putting a tire valve in one end with the other end capped off. Then pump up to the boost you normally run at. I think from after the air filter to before the throttle body should be the way to go. Clamp them tight. You'd be surprised how much 20-25 PSI is.

 

Vacuum lines look fine. Boost test is fine.
I let it warm up and took it around the block and had boost.
No clue why I lost boost in the first place.
Going to take it to work tomorrow and see how it drives.

 

The time I lost all boost was when my intercooler side plastic tank cracked. Running 23psi on the cheap factory intercooler. The other two times were obvious because i had a couple come apart. I do know that the plastic factory bypass valve in the picture you shared are problematic. If it keeps re occurring I would get a forged diverter valve, no tune is necessary unless you get an actual blowoff valve

 

Are you "pending" any CELs? A lot of people dont know that the LNF will pend codes, but not set a CEL. This will limit boost. Check for pending codes.

 

Check the bpv solenoid, the one that sits on top of the intake mani. I would only hit 5 psi. I checked everything and decided to bite the bullet and buy it from the dealership. Swapped it out and back to 25 psi. Headache solved.