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2009 Cobalt SS. The check engine light is on with a generic

code for random misfire and...
2009 Cobalt SS. The check engine light is on with a generic code for random misfire and the boost gauge is all over the place.
JA: Does the light stay on, or does it blink?
Customer: Stays on.
JA: Are you fixing your Cobalt SS yourself? What have you tried so far?
Customer: I got a few stumbles on start up not too long ago and it has 80000 miles so i decided to change the plugs. It got a little better after but now is progressively getting worse.
JA: Anything else you want the mechanic to know before I connect you?
Customer: That's all I have.
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Answered in 8 hours by:
9/10/2017
sprinkles08
sprinkles08, ASE Certified Technician
Category: Car
Satisfied Customers: 23,235
Experience: ASE Master and Advanced level certified. Factory trained with 17 years dealership experience
Verified

Hello and welcome to JustAnswer!

There are quite a few things that will cause misfiring and it will require some testing to determine what is going on. Ignition system or injector issues, fuel quality, an exhaust restriction, and valvetrain/cylinder sealing issues can all cause misfires.

Was the code a P0300, multiple cylinder misfire?

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Customer reply replied 2 months ago
The first time, yes. I didn't notice any misfires and the car was running fine so I cleared the codes. It only took a week for the light to come back on and a couple days later I felt it stumble when I started it. That's also when I noticed the boost gauge going crazy with no changes to the idle. It also still runs fine after warming up.
Customer reply replied 2 months ago
I am going out right now to read the codes again and snoop around under the hood to see if I can find anything obvious.

Ok.

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Customer reply replied 2 months ago
P0300 Multiple, P0302 Cylender 2 and P0303 Cylender 3. I also took a look at the live stream and everything appears to be in sync but the throttle position and MAF are fluctuating a bit more than expected at idle. Also the boost pressure is reading normal even though while it was idling the boost gauge was sitting at 5psi. Makes me think the boost gauge has nothing to do with what's going on.

Did you note a difference in condition of any of the spark plugs when you removed the old ones?

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Customer reply replied 2 months ago
No. They were all the same and looked good. Kind of a dark brown with no oil or fuel on them.

Are you using an actual scan tool and can monitor data?

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Customer reply replied 2 months ago
I have the Bosch dongle for my phone.

Can you see if it's currently counting misfires on 2 and 3?

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Customer reply replied 2 months ago
It doesn't look like it has that capability. All I see on the live scan data pages are the engine sensors.

Does it only run poorly on startup or is it running poorly all the time?

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Customer reply replied 2 months ago
Only on startup when cold.

Is there any smoke from the tailpipe?

Is it using any coolant?

It misses immediately on startup and goes away?

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Customer reply replied 2 months ago
No smoke. Coolant is good. Yes.

You may have injectors leaking then. It would be a good idea to remove the fuel rail with the engine cold, cycle the key to run the fuel pump and see if there is leakage from 2 and 3. You could also try swapping them with 1 and 4 and see if the misfire codes change to those cylinders.

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Customer reply replied 2 months ago
That's a bit easier said than done with direct injection. Looks like I need to find a bore scope.
You can try swapping coils around also but if it only happens on cold start it's more likely to be injector related than ignition.
sprinkles08
sprinkles08, ASE Certified Technician
Category: Car
Satisfied Customers: 23,235
Experience: ASE Master and Advanced level certified. Factory trained with 17 years dealership experience
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sprinkles08
sprinkles08, ASE Certified Technician
Category: Car
Satisfied Customers: 23,235
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