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GMC Forum: P0300 Random/Multiple Cylinder Misfire Detected
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  #1  
Old 11-04-2010, 06:44 AM
itguyredskins itguyredskins is offline
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Question P0300 Random/Multiple Cylinder Misfire Detected

Hello,
I was looking for some guidance with a Random Cylinder Misfire.

Specs:
2004 2500HD 6.0L
202000 Miles

Symptoms (other then code):
What appears to be an exhaust leak from the left side of the engine in a constant air pop noise. It gets quieter as the truck runs and you can't hear it at around 3k rpm.

Things I have done:
Changed plugs and wires
Checked vacuum tubes (which there only seemed to be two)
I don't have an EGR valve
My PCV value seemed fine.
Fuel injector cleaner has been added on multiple occasions.
Unless I did it wrong the propane test did not show anything (tested around throttle body, vacuum hoses and intake manifold.)

Other info:
Truck idles fine under any condition
There was never a code for a specific cylinder and coils are fine
EVAP is not giving any codes
No rough idle or stalling
No hesitation while accelerating
I don't feel any misfires
The engine light will flash and then eventually stay on.

I'm not sure how to check the exhaust manifold or if I missed any vacuum hoses. I'm worried I won't pass emissions. I have not done a compression test, I don't think I need to, plus it's a pain.

Any help is much appreciated.

David
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  #2  
Old 11-04-2010, 09:34 AM
Molson02536 Molson02536 is offline
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Location: K/W Ontario Canada
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Quote:
Originally Posted by itguyredskins View Post
Hello,
I was looking for some guidance with a Random Cylinder Misfire.

Specs:
2004 2500HD 6.0L
202000 Miles

Symptoms (other then code):
What appears to be an exhaust leak from the left side of the engine in a constant air pop noise. It gets quieter as the truck runs and you can't hear it at around 3k rpm.

Things I have done:
Changed plugs and wires
Checked vacuum tubes (which there only seemed to be two)
I don't have an EGR valve
My PCV value seemed fine.
Fuel injector cleaner has been added on multiple occasions.
Unless I did it wrong the propane test did not show anything (tested around throttle body, vacuum hoses and intake manifold.)

Other info:
Truck idles fine under any condition
There was never a code for a specific cylinder and coils are fine
EVAP is not giving any codes
No rough idle or stalling
No hesitation while accelerating
I don't feel any misfires
The engine light will flash and then eventually stay on.

I'm not sure how to check the exhaust manifold or if I missed any vacuum hoses. I'm worried I won't pass emissions. I have not done a compression test, I don't think I need to, plus it's a pain.

Any help is much appreciated.

David
There are tow area's I would concentrate on to looking in to.

1st would be the fuel filter replacement, and i am not sure if your Sierra has the fuel filter built right in with your sending unit. The fuel sending unit also has a life expectancy of 150,000, so anything more then that is considered borrowed time.

2nd would be your knock sensor. There are two knock sensors on your engine and the most common sensor to go bad is the rear one, but replace both if you can since your there. What happens is corrosion of the rear bank knock sensor due to water intrusion into the sensor cavity (another reason for not squirting your motor down with a hose like some think its ok to do) In
fact, a GM bulletin mentions "this condition is more apparent on vehicles in which customers frequently wash the engine compartment".

Replace rear bank knock sensor and build a "dam" around the sensor using RTV to divert water away from the sensor. (swell. make a "puddy dam" that's high tech eh?)"

GM part no. for the sensor is 10456603

Good luck and keep us posted.
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  #3  
Old 11-04-2010, 10:18 AM
itguyredskins itguyredskins is offline
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Join Date: Nov 2010
Posts: 2
Thumbs up Thanks Molson02536

Thank you and thanks for the quick response. I am going to try these out.

David
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  #4  
Old 11-04-2010, 12:23 PM
Molson02536 Molson02536 is offline
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Quote:
Originally Posted by itguyredskins View Post
Thank you and thanks for the quick response. I am going to try these out.

David
Almost forgot, inspect your Fuel Pressure Regulator (FPR). A faulty FPR can cause the same issues you have described. You can check this by pulling the vacuum line from the FPR and if fuel is present in the vacuum lines. Replace the FPR since the diaphragm has gone bad and the fuel is being sucked in to the manifold through the vacuum lines.

Good luck and keep us posted.
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  #5  
Old 12-06-2010, 11:13 AM
QQtrick1QQ QQtrick1QQ is offline
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Join Date: Dec 2010
Posts: 3
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Would be nice if everyone posted their fixes..
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