Hello, i recently bought a cobalt ss sc 2007 and the other day i step on it all the way to the the floor in third to see what this little beast can do and it only read 35 kpa on the boost gauge!??? So i tried it again,but this time in second, and puch it all the way to the redline and it read again 35 kpa (35kpa=5psi). On idle it read -65 kpa. I'm not used to work with boosted engine... is it a leak??? How can i check if their is a leak? Is it the gauge because the car seem to puch a lot despite this problem lol, but the gauge repond very well when i play with the gaz? The car is all stock.
Thanks

 

did your car throw a engine power reduced message? any codes/check engine lights? first id check to make sure your by pass valve isnt seized.

 

Thanks for the reply! Their is no check engine light on it....

 

a stock one should be doing what. 12.5 psi?

 

yeah, i think... Thats what i read everywhere so mine is about half of this lol

 

it could be the gauge but look at your bypass valve ontop of the supercharger its the little circle lookin thing there is a spring loaded valve on the bottom see if its stuck open. also did you notice it idling rough or running rough while driving it?

 

Thanks for the tips!! i will try to check that bypass valve tomorrow To answer your question, nope i didn't notice anything special on idle or when im driving it,only a loss of boost but the car seem to run great except of that.

 

Try lubing the bypass valve rod.

 

i had my buddy call me yesterday with the same problem on his 06 ss/sc i went and checked it out turns out one of his vaccum lines from the solenoid next to the evap purge solenoid had a leak and was causing his bypass valve to stick open it was making a loud noise through the bypass valve...a good way to check if its stuck open is to disconnect the vaccum on the solenoid that leads to the bypass valve (the one to the right of the evap purge solenoid) when you disconnect it it should make a loud nois on the bottom of the bypass valve if it the noise doesnt change you found your problem.

 

Thank you very much for the help!!! I'd check this out after work and give you somes news about it. I did check some hose but i think i didn't look at these vaccum lines but with your explanation i should be able to solve or ,at least, find my problem no matter if it is the bypass valve or the lines . Thanks again! I think it can be a great idea to lube my bypass valve rod too since i'm there lol

 

no problem keep us posted if that doesnt work we can figure something else out

 

When i disconnect the vaccum, it doesn't made any sound at all so i think it may be the bypass valve because the lines seem ok... so i tried to lube my bypass valve but it just don't want to open??? So i look to buy a brand new bypass valve at my nearest chevrolet dealer and they told me it was 420$!!!! I think i'll buy one from ZZPerformance at 99.99$ lol

 

When my bypass went out I felt a major !!!! Difference. My car was brand new and my boost gauge never worked like every other cobalt I had raced or been in.

Bad bypass causes engine power reduction and you get no boost at all or atleast feels like that.

 

when i had problems with my boost i had to change out the boost pressure sensor or wutever its called on the side of the valve cover..cost lik 30bux from a dealership i went thru 2 of em for sum reason

 

ok thanks i should check this out before i'll buy a buypass valve but i tought a bad sensor should throw a engine code?

 

eh not always mine didnt i jus lost almost all my boost and the car became a turd

 

ok thanks i'll check this out!

 

I have a similar problem.

When I unplug the vacuum line connected to the intake manifold I get full boost:




But If I re-connect it, I get 17psi.



Correction...If I connect it, I get 2.5 psi
I don't get it.

 

So you unplug it and just drive and check out the boost or do you plug that line up with something or what?

 

I have the line disconnected and plugged right now. A mechanic told me that it's there to blow off excess boost on decel. what he couldn't tell me is why, when plugged in, it bleeds off all but 2.5psi. been trying to find a vacuum diagram (I don't own a stock hood, which would contain such a diagram) They're hard to find. (tried searching here...no luck, thus far.)

Here's a better pictorial description:



/threadjack...should I start my own thread?? or is this related to OP problem? Sounds like what he was getting too...

 

I finally found my problem! It was the small thing on which the bypass valve is attached to the supercharger. It did not want to move at all when I put out the bypass valve so i use some wd-40 and a screwdriver on it to make it move... now it move with no problem. Put back my bypass valve on it and i push 12 psi now! That thing was stuck and making my bypass valve run incorrectly.

 

please explain this a little bit more I can move the rode connecting the bypass valve took both hoses off and heard no noise and what do you mean by using a screwdriver and wd 40 I don't see where to spraw that

I used to get 12 then now all I get is 3
and I just bouht the car has 120k

 

check the bypass solenoid by doing the boost bypass mod unplug the vac line the comes to the manifold to the bypass solenoid and plug it and see if it builds pressure

 

it sucks in when I take it off it idles crazy like

 

Ok so a bad by pass valve makes it go into engine power reduce cause it fells like mine is the same way there are time when I can push it really hard and then there are time when I do it goes into power reduce mode