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Discussion Starter #1
I have a 07 Chevy Impala SS with Magnaflow exhaust and a K&N air intake. I replaced the spark plugs/wires, #3 Fuel Injector, Intake Manifold, and swopped out both coils (For testing). All the parts are OEM. When I accelerate past 40Mph the car misfires doing a little hesitation or loss of power. When I get to 80Mph its struggles to maintain that speed. I would have to add more gas to maintain that speed or it will lose RPM and power. I got a pressure test done and the pressure is just a little low. I was told to go to the dealer and that want to do another pressure test or cylinder leak test that will cost $300.

Any Suggestions?? :dunno:
 

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8th Gen Antagonist
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Low compression in that cylinder, plus the misfire, maybe one of the valves is hanging open?
 
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Back in Black
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Might try some seafoam first and see if it help. If valve is sticking due to carbon build up this might help.
How many miles on car?
 

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Discussion Starter #5
Might try some seafoam first and see if it help. If valve is sticking due to carbon build up this might help.
How many miles on car?

__________________
_________________________

2012 Impala LTZ
2002 Buick Regal LS 335,000 miles
2000 Buick Regal LS 182,000 miles
1998 Olds Silhouette 3.4V6 177,000 miles
1996 Olds Cutlas 3.1V6 293,000miles
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@12ltz

I will try the seafoam and provide you some feedback. It has 90,000 miles on it
 

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Discussion Starter #6
Might try some seafoam first and see if it help. If valve is sticking due to carbon build up this might help.
How many miles on car?

__________________
_________________________

2012 Impala LTZ
2002 Buick Regal LS 335,000 miles
2000 Buick Regal LS 182,000 miles
1998 Olds Silhouette 3.4V6 177,000 miles
1996 Olds Cutlas 3.1V6 293,000miles

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@kingnutin

I’m not sure if one of the valves are open but I’ll give it a look.

http://www.impalaforums.com/members/kingnutin.html
 

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8th Gen Antagonist
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If one treatment improved it, keep at it. More than likely its just carbon causing the problem.
 

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Discussion Starter #9
The misfire stayed. Basically its like a small rough idle and I'm assuming its missing before acceleration. Maybe some type of slug or carbon build up causing a valve not to properly close.

I used a product call Gunk Engine Flush and I started to feel results instantly. There barley any idle issues but I can hear a whistle sound. I think my misfire could be coming from a vacuum leak. I still have the misfire cylinder 3 but I'm not feeling any performance issues.

Any suggestions?
 

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If one treatment improved it, keep at it. More than likely its just carbon causing the problem.
Why does the carbon build up in the first place? Is the fuel not burning correctly?
 

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8th Gen Antagonist
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13,660 Posts
^ Basically, usually it accumulates more from low quality gas, whether it be arco, or just winter blend, it adds up. Techron, and other proprietary additives help break it down, but best bet is to run seafoam every few tanks or so.
 
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