Bypass valve hoses atmospheric vent
 

Hey just got a supercharger put on, no major issues, noticing everyone else has there bypass valve houses a little different then mine.

I know being a force inducted NA car, one port is atmospheric vent now, the other port should be going into the supercharger, but should that be the top or bottom nipple?


https://cimg4.ibsrv.net/gimg/www.cob...0f8f8282c4.jpg

Top. You have it wrong in the picture

Really? WOW came like that from zzp, boost is good, bypass valve seems to be working not getting overboost. But right I will change the hose thankyou!!
Super quick reply!!!

https://cimg0.ibsrv.net/gimg/www.cob...bcd41cdbdb.jpg
At rest the bypass butterfly valve is closed. You can see in this picture that when there is (V)acuum on the top of the actuator diaphragm it will pull the rod up/in which opens the valve to allow air to circulate to prevent the supercharger from trying to suck air through a partially closed throttle body. The bottom portion will do the same thing when pressurized. The LSJ solenoid will route boost pressure from the IM to the bottom port when the ECU detects issues and commands it to pull boost.

Switched the hoses out yesterday thanks guys... boost feels a lot more controllable now

Idle fluctuation and bad gas mileage, plus vaccume line problems
 

Hi guys so I have been shaking my head all day at this cobalt, I recently bought the car at the start of winter, and had idle fluctuation and bad gas mileage from the get go. When I got the car it was known that it has, #60 injectors, a smaller pulley ( just over 3'') and is stage 2 tuned. (whatever that means) and CAI. Started with the air intake, which was wet and discusting. Took it off and ordered a new one. Comes in tomorrow. In the mean time I am trying to diagnose the bypass valve. While idling the valve opens all the way away from the stopper is this normal? Then springs to what I call closed when given throttle. The valve does not suck air at idle through the bottom port. And does stay open when I put my finger over bottom port when opening it with my fingers. There is a vaccume line missing from the bottom port of the bypass solenoid which I cannot figure out where that would go on the internet anywhere. Any help is greatly appreciated. Picture attached is nipple with missing hose.
https://cimg6.ibsrv.net/gimg/www.cob...bae36d894d.jpg

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To my understanding the lower hose goes to your boost actuator, very likely the owner prior disconnected it, allowing it to potentially "over boost."
Pretty sure that actuator is in the drivers left corner of the engine bay. It sounds like your bypass valve is operating properly to me tho..
The top bypass valve hose should just go from bypass to supercharger. As for testing, go down the street and boost. If you hit 10-12 psi your good but if you only got 3-4 psi there's something wrong.

I'd recommend taking a look in your manifold, cleaning that and the throttle body..

Vaccume
 

I also should add if anyone actually reads this, that I am getting a P0171 bank 2 lean. I am also concerned that the ECM just isn't flashed properly for the upgrades that it has, ie upgraded supercharger and #60 Injectors. Note I do have an unburnt gas smell as well. Here's some more pics of the other vaccume lines that I have ran. I replaced a couple that were old and brittle.
https://cimg7.ibsrv.net/gimg/www.cob...03a4a735bc.jpg
Hose I'm holding here goes to the back of the bypass solenoid and to the intake manifold under fuel rail
https://cimg5.ibsrv.net/gimg/www.cob...fb6c903fe0.jpg
Hoses here, clear hose goes from supercharger to top port on bypass valve, bottom port on valve goes to top port on solenoid, but bottom port on solenoid has missing hose.

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Hey man, thank you so much for answering!! That is helpful! I do not want the car to overboost haha. It has enough problems as is. Now my question is, with this just unhooked will it not cause a vacume leak directly out of either the solenoid or the other end where its supposed to go?? I cannot drive the car until tomorrow when a new air filter comes in. But I am having vaccume leak like symptoms, ie horrible gas mileage, idle fluctuation as well and unburnt gas smell. But I revved the car in neutral and think I made at least 5lbs of boost! Could have been 10

I should add that I am getting a P0171 code fuel trim lean bank 2, I did clean the throttle body already had alot of gunk in it for sure.

Pics of my vaccume lines
 

When I last attempted to fix the problem I cleaned the throttle body very well, the mass air flow sensor, which I do believe is working because when I put my hand over the CAI with no filter installed the car bogs down almost exactly the same as when I drive it and come to a stop light. Massive bog then it does an uncontrolled rev to make up for it. (I'm hoping my wet and rusty air filter had alot to do with most of this) I replaced a few vaccume lines as well.
https://cimg7.ibsrv.net/gimg/www.cob...03a4a735bc.jpg
Hose I'm holding here goes to the back of the bypass solenoid and to the intake manifold under fuel rail

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It shouldn't. My bottom bypass valve nipple is exposed to atmosphere (no hose plugged into anything), as being a NA car I don't have anything to plug it into anyway..
If the diaphragm inside was torn, then yes maybe, but I don't think yours is. Hopefully an LSJ guy will join the party here soon

Oh ok, interesting. I tried to post some photos of all my vaccume lines that I know of and where they all run and what I replaced of them but I think it said it needed to be approved by a moderator,

Kk yeah to my understanding when you fire your car up the bypass valve should move a little, ie the diaphragm apposing the engine vacuum making it move.
If the diaphragm inside was broken, there’d be nothing to apposé vacuum and thus it wouldn’t move.
So I think your bypass valve is fine.

however I’d recommend taking it for a drive tmr try boosting and see how high she goes. If it’s still 4-5psi in gear somethings wrong. If you do reach high boost, you’ll know to look elsewhere

Could just be a vacuum leak elsewhere. Clean MAF, clean the matting surface between your manifold and head, supercharger and manifold, double check throttle body to supercharger. Check PCV hoses, make sure your oil cap is sealing, valve cover isn’t seeping, etc maybe even break booster.. could test your purge valve pretty easily too..
Could even be now that the Throttle body is clean, the computer thinks it’s gummed up still* and is getting way more air than predicted, you could resetting the modules by disconnecting the battery..

[QUOTE=G5ALIVE;7743474]Kk yeah to my understanding when you fire your car up the bypass valve should move a little, ie the diaphragm apposing the engine vacuum making it move.
If the diaphragm inside was broken, there’d be nothing to apposé vacuum and thus it wouldn’t move.
So I think your bypass valve is fine.

however I’d recommend taking it for a drive tmr try boosting and see how high she goes. If it’s still 4-5psi in gear somethings wrong. If you do reach high boost, you’ll know to look elsewhere

Could just be a vacuum leak elsewhere. Clean MAF, clean the matting surface between your manifold and head, supercharger and manifold, double check throttle body to supercharger. Check PCV hoses, make sure your oil cap is sealing, valve cover isn’t seeping, etc maybe even break booster.. could test your purge valve pretty easily too..
Could even be now that the Throttle body is clean, the computer thinks it’s gummed up still

Again thanks for all your help so far, but yeah when the car is running the bypass valve is definitely under pressure, you cannot move it with your fingers when it's idling, I actually have a video of it engaging, but I too think it's working. I will take it for a spin tomorrow and write back and let you know what the boost gauge reads. I just had a look at the engine oil cap, did have a bunch of dirt all on the o-ring, boy that would be silly if that was all the problem is 😂 I also unplugged the battery in hopes of resetting anything. I read somewhere you can reset the idle with gypsy cycles of the key and gas presses, but wasn't too keen to attempt until I know something else isn't wrong. How up are you on the different kinds of tunes for these cars? This car supposedly has stage 2 tune. I am unaware what all that entails. I assume the supercharger pully? Or Possibly ECM tune?
When you say clean the mating surfaces, are you suggesting I take the supercharger and Intake right off the car? Looks to me that neither have been removed since at least a few years ago haha. Are they're gaskets under both of those?

No problem I'm an LAP guy (2.2l vvt) with a supercharger now but I've read probably a few hundred threads now chasing down problems of my own, reading thing's that don't necessarily pertain to my engine.. Hopefully an LSJ person will offer some advice based on their experience with your particular engine.

But it definitely sounds like your bypass valve is working just fine. Lol it's a stretch yes but still possible. Hard to say, lots of companies offer stage 2 packages, but If I had to guess I'd say it has a GM stage 2 package, 3.1" pulley for sure and adjustments to your fuel, air and timing. Stage 2 would essentially refer to your supercharger pulley size, depending on where it was bought from different supporting mods may or may not have been included tho.

There's a gasket for the head to manifold, manifold to supercharger, and supercharger to throttle body. If your able, it's a possibility absolutely. And yea I do mean cleaning the surfaces with a microfiber cloth and re-installing things with proper bolt torque sequence.
If its a little more inclined then you like, start with things that are more accessible like your break booster vacuum hose, pcv hose, make sure the purge solenoid isn't stuck open or something. Clean the MAF, reset the computer one more time after that and I'd say go for a drive see if it's any different after you've got the new intake, air filter, clean maf, clean tb and a computer reset.

On second thought tho, a gas smell would definitely lead me to believe there is a leak on the valve cover. I had a breather on my PCV port (on the valve cover ) for a few months and it let out lots of gasoline smell, it sucked lol.
If there was lots of dirt on that oil cap it could be your smoking gun

Ok, so after some research the pcv line on the cobalt I think is one of the plastic lines.. I think, I'm not exactly sure what pcv does other than it's in the intake. And the brake booster line seems like it's just breather line that comes off the supercharger? then goes either into the brake booster or just loosely into the firewall, I'm unclear apparently it's a good place to seafoam to clean out the intake system, which I may try before I go to the lengths of dissamebling

PCV hose runs from your intake to the valve cover. It allows positive crank case pressure to be vented into your intake tube. Oil/gas. Should be a pcv hose. This is the hose that got the Throttle body all dirty.

The evap purge solenoid attaches to your throttle body with likely a plastic tube. That little valve opens and closes venting fuel vapours into the intake and can break leaving it in open/closed positions.

Break booster hose attaches to your supercharger. Though if your not experiencing breaking issues, probably not a likely source of a vacuum leak.

Hey man, thanks for that, I found all of the hoses you mentioned, and none have any cracks or anything I can see. I sprayed some throttle body cleaner into the supercharger through the brake booster port. And tested the purge solenoid by blowing air into it with my mouth, and it seems like it's a vaccume in there therefore that should be good. Another thing I should add that is hopefully making the gas smell is that someone straight piped the car as well smh. But it's all after the cat so I assume it won't affect 02 sensor readings. I do plan on putting a nice muffler on the car if I can get it running right. The new air filter should come in soon I will update you on the boost psi
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That could probably do it, maybe a little rich idle too.
Correct the only O2 sensor that really matters is your pre-cat/ upstream one. The down stream/ after cat O2 sensor is just used for a catalytic efficiency test, essentially validating the cat is there.

​​​​​​Oh yea baby! Just got the air filter put on and it definitely is aloooottt better. And the car is definitely building boost. It pulls 80kpa on the regular, in fifth on a decent pull I had it at 90kpa I believe that's normal boost right? It still does do its self controlled revving thing a little. I should note that when it dips down under idle say 550-700rpm it goes deep into a vaccume like - 80kpa is this normal? Ish? Maybe next I'll do spark plugs.. Where do I begin to find out what kind of plug to run?

Also when the car is idling it sits around - 50kpa when I first got back from the drive it sat at - 60kpa until I gave it a few Revs, if that helps at all.

Nice man good to hear! Yeah that's a very typical boost range 11.5-13psi, definitely not having problems with your bypass actuator or boost actuator.
-80 kpa would be like 23.5inch mercury.. That's a lot. But 14.7-17.7 idling, that's a good vacuum.

Something looks odd here, again I don't have an LSJ but looks like that hose is either punctured by the hose clamp or missing it maybe? on the right side
https://cimg8.ibsrv.net/gimg/www.cob...ca12acf4b4.jpg