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Category: Chevy
Satisfied Customers: 26261
Experience:  ASE certified tech ADVANCED LEVEL SPECIALIST. Wisconsin certified emissions state inspector
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2009 Chevy Cobalt: ) and the service engine light came on..cylinder

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I have a 2009 Chevy Cobalt. It started missing (really bad when a/c is on) and the service engine light came on. I took it to a shop and was told it was in the #4 cylinder. and to replace the plugs. I did that and it still missed and engine light was on (after it was reset) So then I was told to replace the coil pack. I did this, ran fine for about 30 minutes and then the engine light came on again. The shop then did a compression test on the cylinder and said that I only had 23 lbs of pressure in it. Said the valve is burnt and would have to have the head removed and it fixed. Is this right? Or should I get a second opinion? The car seems to run fine except for a slight missing (which gets worse sitting at a stop light with the a/c on).

Any advice would be appreciated.


Did you watch them do this compression test? Also, did you have them do a cylinder leak down test on number 4 cylinder?
Customer: replied 5 years ago.
I was there when they did the compression test. He hooked up the gauge to the cylinder and I started the car and then turned it off in a minute or so and he showed me the gauge reading 23lbs. I'm not sure what a cylinder leak down test is so I'm not sure if he did it.
Ok.. as long as the compression gauge that was used is accurate, then this is a major problem. The cylinder 4 has low compression and it could be due to a few different things. A cylinder leak down test will tell you where it is leaking. Intake valve, exhaust valve or the piston or rings. If the piston rings, cylinder wall or piston itself is bad and leaking causing your compression to be low, then it would be pointless to remove and fix the cylinder head. But if he is sure that it is a valve, then yes.. replacing or rebuilding the cylinder head will fix this condition.
Customer: replied 5 years ago.
So I should request that they do a cylinder leak down test before going any further into it and possibly causing more unecessary expense for a problem that can't be fixed by rebuilding or repairing the head?
You got it!!
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