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post #1 of 7 (permalink) Old 11-16-2016, 04:45 PM Thread Starter
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Possible Bent Valve?

2008 Cobalt LS 2.2L (L61) automatic with 123,000 miles on the clock

Unfortunately, I don't know much about the history of this car. Seller mentioned the timing chain was replaced at a local Chevrolet dealership a few months ago. Unsure if it actually broke or not. The OBD scanner shows P0302 error code; cylinder 2 misfire detected. Check engine light is on and will sometimes flash for about 30 seconds, then return to a solid yellow. Installed a brand new spark plug gapped at 0.040 as well as a new coil for cylinder 2. I noticed the old spark plug was missing the center electrode and side electrode is discolored (light gray almost white).

Idles extremely rough, can feel the engine shaking in the drivers seat. Needle stays steady at 800-900 RPM despite it feeling like it is going to stall. Smooths right out once you accelerate. Runs fine on the expressway as well. Been averaging 20-23 MPG in mostly all city driving. Which seems low for this car?

Unsure if this is related or not but I have noticed the gauges will dim every so slightly and flicker at night (headlight on) while at idle.

Any idea what might be causing all this? Bent valve? Broken spring? Sludge buildup? Any help getting my new work car running better will be greatly appreciated!

Video of exhaust at idle:
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post #2 of 7 (permalink) Old 11-16-2016, 08:07 PM
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You could do a compression test to see if cylinder 2 is lower than the rest. Pretty sure that'd tell you if there's a bent valve or bad ring seal or something like that.

@Coby7 any other ideas?


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post #3 of 7 (permalink) Old 11-16-2016, 09:11 PM
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I always start with a compression test along with inspecting or just changing all the plugs while they are out. Also inspect all of the ignition coils. If compression was good I swap coils from the misfiring cylinder to a different one and see if the misfire moves with it. Also, while the engine is running use a long screwdriver or something similar, put one end on the body of the injectors and put the other end to your ear. Should be easy to hear the injector firing, you will hear a lot of clicking.
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post #4 of 7 (permalink) Old 11-17-2016, 04:37 AM Thread Starter
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Thanks for the replies!

I don't think it's an issue with the coil. The scan was ran before and after replacing coil #2. And both times it registered a cylinder #2 misfire.

I will hopefully get my hands on a compression tester this weekend.
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post #5 of 7 (permalink) Old 11-17-2016, 04:43 AM
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I think you will find low compression on cylinder 2 because that sure sounds like a bent or burnt valve.

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post #6 of 7 (permalink) Old 11-17-2016, 04:56 AM Thread Starter
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Burnt valve? What is that?
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post #7 of 7 (permalink) Old 11-18-2016, 07:09 AM
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Quote:
Originally Posted by blujax View Post
Burnt valve? What is that?
I hadn't heard of that either, but found a good thread explaining it.

engine - What exactly is a "burnt valve" and what causes it? - Motor Vehicle Maintenance & Repair Stack Exchange


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