Hey everybody!

So just this past friday I brought my 2006 Cobalt ss/sc to an auto shop to get a compression test. I just wanted to see what i was sitting at for compression. No real reason why i wanted it done. My car ran perfect before i dropped it off. i picked it up Friday night and there is something wrong. As soon as I hit boost you hear a lot of exhaust noise along with no power. I brought it back to have them that night and said they would look at it the next day.

I talked to them about how they did the compression test and they said they didnt disable the fuel injection system. They also said they stuck a screwdriver into the TB and laid all the spark plugs on the valve cover. All seems right to me but not disabling the injection system.

But they do not have any idea what could be causing this.

Could that be the reason for my car doing this? Just curious if anyone had this problem before or someone can help me out? What to change, what to clean? Any ideas is greatly appreciated.

 

Disabling the injectors is to prevent in needed fuel from spraying into the cylinders. pretty standard for a compression test.

 

did they hook up all the sensors correctly ? any CEL's ?

 

They just destroyed your tb. Its not a drive by cable system you cannot stick a screwdriver into the TB on a drive by wire system. I'm going to guess its throwing codes for the TB, take it back to the shop and tell them they owe you a TB since they decided to stuff a screwdriver into it

 

They said they didnt unhook anything. just the coupler on the TB. Sorry if there was confusion. But they didnt disable the fuel injectors. So it was spray gas into the cylinders without anything to ignite it. and no CELs.

Car shakes slightly at idle now too.

 

I'm not super familiar with lsjs but normally if you hold the throttle wide open while cranking it will disable the injectors. Did they play with the bypass valves on the supercharger at all? Is it making any boost?

 

They told that it could be access gas in the cylinders and to try putting back in ac delcos. And they didnt say they played with the bypass valve. Its making boost but makes a lot noise.

 

and what were the results of your test?

sometimes people fail to tighten spark plugs all the way and that will cause issues...

change your oil

 

cylinder 1 got 175/170/175. Cylinder 2 got 180/175/180. Cylinder 3 got 175/175/175 and cylinder 4 got 185/185/182.

I torque them to spec.

 

I appreciate all of you for coming up with ideas! Ill look into all options.

Would i see physical damage to the TB? would that cause it?

I will get my oil changed too. Almost due for one anyways.

 

The car would run like crap and you should throw a code. The TB blade doesnt like to be moved by physical force

 

Would it run like crap all the time? Right now it just runs like crap at boost and idle.

 

Depends, a local to me had a TB going out and it would randomly decide to run like crap. One startup it would be fine, the next it would freak out and run rough not like boost. Connect a scanner and see if there is a stored code

 

This is everytime i start up though. Ill have them run a scan to see if there is any but the CEL never showed up as far as i know. I dont think i could get them to replace this on a hunch either.

 

Any other ideas before i go out and buy a new TB? looking at all options! Or is anyone selling a good TB?

 

So i called them back and they agreed to a scan for CEL although the CEL did not show up. I asked him about the wire TB and he said that they need to relearn where open and close is but it might not be able to because it has a tune on it(Hptuners).

 

Hmm. So no code popped up on the dash? Tell ya what i read over this again and sounds like you randomly got an exhayst leak or also perhaps your cat clogged. Are you on an oem exhaust?

Jack up the car, stsrt it and quickly feel around the sccordion between the header and cat. And any other spot you can (before it all gets to hot)
If you feel a leak i got news for ya

If no leaks are felt, remove an 02 sensor and go rip down the street. If it feels better than it did you may have a clogged cat.

Would seem wierd since the guys reportedly didnt touch anything there but sometimes unrelated things happen at convieniantly incoveniant times. Or even all the stsrting they had to do might have shaken and bucked the engine enough to break a flexpipe. Or if the injectors werent disabled some unburnt fuel caught up in the cat. Just spitting out ideas.

 

Good call on the potential clogged cat. OP what are you boosting to when you try to go WOT?

 

Yeah that too.

 

I wasnt going to update on here until i figure this out but....On the way to bring my car back to the shop so they could look at it the next day. I drove in boost for a little bit where it acts up and i was able to get a flashing CEL, so i let up on the throttle right away. After about 3 seconds its stop flashing and went away completely. So im having them scan it today.

And yes im on stock exhaust.


As for what boost im hitting. I havent tried seeing how hight it goes but im fairly certain it will reach 12.

 

Flashing CEL is for misfires. You need to get a code reader for yourself. Super cheap with Torque app on Android.

Secondly. With a flashing CEL like that I would double and triple check the spark plugs and coil. Maybe they weren't put back together right or were under or over tightened. Maybe the plugs gap got screwed up. Maybe a plug got ruined.

Several things to check. If you check the CEL it may tell you the cylinder to start on.

 

I replaced my NGK ones with ac delcos(torqued to 18lb ft) to see if that works. i checked my wires. all seem good to me.

Maybe a coil pack has gone bad?

 

Get a code scanner for yourself, the torque app one is nice. That will help greatly in determining what is wrong

 

yea i will purchase one in the near future for sure.

 

Yes a coil pack could be bad for sure. Or got damaged when the work was done.

Parts stores like autozone will check codes for free as well. Just write them down and post them here.