silverbullet08

This should be a sticky if we can make it, After about an hour of trouble shooting and test runs i have found out why my car would only boost to about 10 psi, sometimes 14psi, and other times only 5psi. Its another one of GM's contraptions that hasnt worked for me. I have heard others talking about this so i did some research and turned some bolts and this is what i found. THIS MAY ACTUALLY BE A BOOST MOD. I am boosting 18psi now that i have done this. Im not sure what the factory boost setting is so correct me if im wrong.

HOW IT WORKS:
The LNF has a recirculating bypass valve/Blow off valve located on the passanger side of the turbo. It is held on by three 10mm bolts and a vacum line in the middle of the plate. When throttle is released vacume travels throught the lines pulling back on the valve and releasing it backwards through your air intake/air filter after the MAF sensor.

THE PROBLEM:
On a scanner or code reader, you will see a turbo/supercharger bypass mechanicle code. You may get random codes about unexplained air/fuel misreading. Your car will boost to the propper level sometimes but not always, seeing a varitation of boost levels between 0-10psi.

WHAT CAUSES IT:
There are three actual problems that can occure, a leaking vacume line, actual bypass valve stuck in the turbo, or the GM engineered vacume tank may be leaking or have a bad check valve inside. The tank is there to help build and store vacume to help with "faster spool times" and make it more "responsive". IMO it does nothing but get in the way and cause problems. I felt like it spooled faster and was more responsive after i removed it.

THE FIX:
If it is your vacume tank you can easily bypass it in about 3 mins. There are three vacume lines coming up the front of the motor by the dipstick. One from your MAP sensor and other two from your vacume tank. First remove the Vacume line that comes up and goes into the top of the intake manifold then remove the vacume line closest to the dipstick on the bypass solinoid "where they all meet". cut about 5"-6" of vacume line off one of the lines you removed and plug it into the manifold and where you just disconnected it from the solenoid. Go for a drive and see if it solves it. If so then you can reach the vacume tank from the underside of the car to remove it "one bolt".

After doing this my car felt 10x more responsive, and boosts to 18psi consistantly. IDK what the actual factory boost setting is but it feels alot faster than what it felt at 15psi. And of course you should see a little more power with a little more boost but it made a pretty good difference for me.

berto

would this work with us who are tuned??
me for example have a PPC BSR tune from HAHN and was originaly boosting 22psi
then one night my cel came on and now i boost 2psi
i thought it was a boost leak but not sure...p'm me if u can answer this

silverbullet08

definet possibilty! try doing the tank delete by swapping the lines and see if it fixes it, cant hurt anything, if you use a extra piece of vacume line instead of cutting yours on the car you can put it right back to stock and only takes literally 3 mins to do.

DillySS

So what your telling me is there is a area that vacuum is stored to give more turbo response? If you delete the tank and make a "psuedo" tank out of one vac line then this will solve boost problems.

In a recirc system, do we need all that storage of vacuum?
If not, why isn't everyone with an LNF chopping the tube just enough to fit in the two holes?
With less vaccum stored will the turbo respond less quickly?

Really I think I am asking the question do we need a box to hold vacuum or can we use a rubber tube? (especailly since some of us have the Dejon spring)

SportredSS

Well, first off There's no difference in sound or drivability with the dejon spring, waste of $10 IMHO...
Secondly, if you plan to keep it stock a few more psi is ok... 15 is stock.... This idea is interesting but a few pics would help those get a BIGGER picture of what lines\area your talking about...

fakameanrepresent

iTrader: (4)

pictures and a how to would be great, thanks.

steddy2112

iTrader: (1)

Scythe_Snake

hm. subbing with pics and stuff. I wanna see what you're talking about.

bowtie32

iTrader: (3)

I would like to see pics aswell. Thanks

fakameanrepresent

iTrader: (4)

X10000000000000

berto

this is basicaly the set up i got except i have an HKS bov...not my engine bay but this is the only pic i could find
i think he wants us to disconnect the lines circled in red
the ones in yellow is what i did on my car.....sorry for a small pic someone plz help on this

fakameanrepresent

iTrader: (4)

i can't really picture it, its so small.

berto

my bad...my laptop is acting up
silverbullet08 we need pix!!!

Zander916

I THINK this is what he's talking about. (also waiting for pics)
The two actually circled are the ones to disconnect and bypass. I'm not 100% though...



EDIT: I got brave and tried it out. After looking at the picture I did and reading his description I couldn't see it being different.
CONFIRMED: According to the gauge it appears that I gained in the ballpark of 1 psi. It's not much at all I know, but it was free. Can't argue with that. I am BSR tuned by the way.
Will you feel it in the seat of your pants? No.
I'm unsure about spool up response. I can't tell if it has changed. However, the BPV seems to react quicker and also dump the pressure faster. Makes sense too if you think about it. The tank is just more volume for vacuum to be pulled on. With only a hose in it's place the reaction is quicker. (MUCH less volume) Seems like it's a bit more audible for this reason but I'm unsure. It gives me the impression this vacuum tank was designed pretty much just for the NLS feature. I don't use NLS but I did a 2-3 NLS while I was out and it worked just fine.
So just take a single piece of hose and run it from the top of the manifold to the solenoid. (join the two circled with a single piece)

No CEL's or anything. I'm gonna keep it.

Thanks to the OP for sharing! Can't wait until more people try it to get their impressions. I just did a quick 10 minute drive.

Oh, and there was a thread quite a while ago of some people with aggressive tunes experiencing part throttle compressor surge. I have a a feeling this just might be a cure if not help quite a lot. Just a feeling...

turbo_chevy_cobalt

i will be trying this when i get home to see if it helps anything with the stage3 kit

oopsitouchedmyself

iTrader: (2)

hmm...i'll have to look into this today or someday..thanks for sharing.

ninja44

iTrader: (1)

So remove the hose from the top of the intake manifold and the one from the top of the solenoid (the one nearest the front of the car)? In the big pic above they are the ones that are NOT labeled and connect them together? What do you do with the 2 lines that were disconnected? Do you plug them or leave them free to air?

turbo_chevy_cobalt

i did it at work drove home only real thing i can tell is that the bov blows off better and a little faster.

ninja44

iTrader: (1)

Are the unplugged lines left open to air?

crazysteve

going to try this tonight...mine has been giving me fits the last few days.

turbo_chevy_cobalt

yes the two that go to the black box looking thing under the intake manifold i would put pic up but dont have a working camera

Zander916

Yep, that's a definite. I admit, I could just be dreaming about the 1 psi... looked like it. But I don't stare at the boost gauge all that much.

rdskin21

There is no factory boost setting. The car on the stock tune will make no more than 260hp and 260ft/lbs torque, and will produce up to 21 or so psi in order to do so. Most Cobalts seem to produce around 15psi though, stock.

Terminator2

Correct, most produce 15psi stock. I have seen some up to 20 psi stock but the total pressure is always the same 205 kPa. So, if one is at sea level 205-100=105/6.89 = 15.24 psig. If one is 6K feet above sea level 205-80=125/6.89 = 18.14 psig.

alex_mcg

Sounds to me like the closer to stock, the bigger the gain.

The question is, do I have the ***** to try this? Can you just unplug the two tubes, see what happens, and then plug them back in? or are they not able to go back on once they are removed?