Ok I have a 2009 Cobalt SS mods are Catless Down Pipe and GMS1.

The issues are while driving normal down the highway at 65-70 MPH keep contstant speed the car feels like its hesitating like jerky feeling and my boost gauge reads about -5 vac or so. when i am having this issue I can hear the the recirc blow off a few times, but im not in boost. Also when I am at Idle the boost gauge usually sits at about -20 Vac but then i get this wierd noise from the motor sounds like it got out of whack and had to adjust its self and the boost gauge moves as you can see in the video from -20 to like -10. I know most of you will tell me to take the car in cuz its under warranty but I want to get an idea of what the isuues might be cuz I dont want to take my Down Pipe off and tranny mounts to take it in if i dont have too.

Any Ideas of what it might be??



video
YouTube - 2009 Cobalt SS boost

 

Are you throwing any codes with the catless downpipe, and by codes I mean exactly that sometimes they won't trigger the CEL.

 

I was throwing codes for the MAF ( due to K&N airfilter oil ) which i cleaned and put the stock air filter back in. I was getting at CEL when I first installed the DP I did the Spark plug defouler Mod and the CEL never came back its been like 3K miles. I havent had it checked as of lately for any codes though maybe I should and there is no CEL this has been going on for a while.

 

Is the car still messing up?
when you have the issue does the car not make more than 5 lbs boost?
and when you let off the gas (no matter if you have boost or not) will you get a really quick flutter sound?

Do you have the gms1? gms1 sensors?
sounds like an issue with the lower charge pipe sensor messing up.
the wires corrode and the sensor eventually fails, you need to solder the wires and change the o-ring/sensor and do some shaving of the pipe.

do some searches, there are tons of posts about this

 

No i was having these issues that you stated above when i had the K&N air filter but after i put the stock filter back in and cleaned the MAF and lower CP sensor I havent had that issues anymore of the 5lbs boost just this wierd hesitation and boost at idle.

 

I have the same problem as you. Ill post my vid up in this thread hold on. it almost feels like the car is lurching like im rapidly tapping the pedal.... but im not

 

YouTube - VID 00000-20100730-2013.3GP

this is my problem. At idle. No codes, no CEL

 

My GF says "is it cause your brake's not on" LMFAO

 

LMAO!!!!! I heard that and I was like wtf?!?!

 

Women.........

 

Sometimes if I start my car after is has cooled down a couple of hours from normal operating temp my car will idle wierd and my gauge will go to -60kpa to -20kpa then back to -40kpa

 

I drove my car for 30 miles and it was 65 degrees outside this was after i got home and pulled into the driveway. Looks like im going to have to put my stock parts back on and take it to the dealership.

 

You mean like this lol?:
when it does this my exhaust sound as if i have cammed the o'l lnf

 

the dealership will probably tell me that they couldnt replicate the problem and say the car is fine, im going to have it scanned first before i take it in to see if i have any codes.

 

Possible that the cam phasers are adjusting and causing just enough load to change the vacuum

 

well if they do figure it out .... if ... lemme know haha its so intermittent and only started a 1-2 months ago.

 

The funny thing is I know what the clicking noise is the sound of the Direct Injection, but then i hear this weird clicking it doesnt sound right sounds like its coming from the valve cover and thats when the car acts stupid.

 

I havent had the 5lbs of boost and fluttering issues until after you posted this you.......Im really really thinking the Lower Charge Piping Sensor is bad i am not sure if they soldered.

 

Oh, oh! I know what it is!! lol

The search button is great, it would have showed you these threads I made

https://www.cobaltss.net/forums/2-0l...le-wtf-216124/
https://www.cobaltss.net/forums/2-0l...issues-217451/
https://www.cobaltss.net/forums/2-0l...r-gms1-230079/

As you can tell by the dates on these threads I was having the issues, same ones youre having, for months intermittently.

The third thread has the outcome and diagnosis after bringing it to the dealer.

I had been getting CELs like I mentioned in the first thread, they were MAP sensor codes, which is the sensor replaced in the GMS1 kit.

The dealer told me it was a "boost pressure sensor". I wasnt sure what they were talking about, judging by the DTCs I thought it was going to be the GMS1 sensor being poorly installed. Turns out when I picked the car up and looked at the service slip the part listed as being replaced was the GMS1 MAP sensor after all! The service writer probably told me it was a "boost pressure sensor" because he didnt think I'd know what it was or something.

So far its been fine for almost 2 weeks....we'll see if it lasts. I actually took my Dejon SRI off because I thought that was the culprit.... I may put it back on now



EDIT: Out of curiousity what do you peak for boost at WOT? I was spiking AND holding 24-25psi. Since Ive had the issue fixed the most I boost is 21-22.


.

 

I did seach, but thank you for your help i will be taking the car into the dealership soon.

**I Spike like 23 then settle down to like 20-21**

 

I was just kidding about the search thing. No problem, I think its ridiculous there have been so many people with this issue. It was stupid to have the sensors installed with butt connectors.

 

i installed my own connections and i soldered and shrink wrapped them, didn't have the problem till 4-6 months later...... maybe i have a small boost/vacuum leak?

 

***UPDATE***

Drove the car this morning the CEL came on scanned and got code P0236 boost sensor circuit I took the car to dealershipthis. Morning they are going to look at it and also replace the power steering pump. I will keep you all updated when I go to pick it up.

 

Thats what I did.... brought it in and had them do the GMS1 issue and PS recall at the same time. Good luck, let us know how you make out. Im betting itll be the same problem as mine, but we'll see

 

Wow so I spoke to the service manager he said the codes were logged codes and that the check engine light came on while I was in 3rd gear doing 75 MPH I was like wtf??? He said they cleared the codes and the car is running fine and I told him that the lower TMap sensor was probably bad he said if it happens again to bring it in again. I took the car in with my Down pipe still installed they didn't say nothing about it!