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Discussion Starter · #1 ·
We have a 2005 Chevy cobalt about 115,000 miles .we are getting a check engine light and the p030 code .I’m doing a compression check on the motor before replacing the coil/ignition module and plugs .on cylinder 1 I’m getting a reading of 120 ..on all other cylinders I’m getting a reading of 150..is this too low or still in spec??appreciate any advice !!
 

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Seems you have low compression on that one cylinder. About 150psi is ABOUT reasonable. With one at 120, that one is low.
Did you add a squirt of oil into that cylinder and check again?
If the pressure comes up, then it indicated worn or broken ring/ rings...
If it stays low, then you know you have leaky valves
 

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Discussion Starter · #4 ·
I put some oil in it and re tested it ,got 150 with oil.so ya I’m figuring it’s ring based.my question is that 125 compression causing the misfire ?is it worth changing the coils and the plugs and will it work ok at that 125 compression?thank you for your advice .
 

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Yes it can definitely cause a misfire that won’t go away with a new coil or plug on that cylinder. It is unable to ignite the fuel as well as the other three cylinders. 150 psi sounds a little low as well, but may be in spec. I would expect 160-180 psi. It really sounds like the engine is really worn out. I really don’t know what the cause would be. But if I had to guess with mileage that low, it would be lack of maintenance. Things like oil change intervals that have gone way too long can be a factor. I also know that many of these engine just seemed to have wear issues. Lots of oil consumption problems are what I’ve read about. And that’s going into the newer Ecotec engines as well.
 

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120# isn’t great, but it should be more than enough to fire.
We have engines, at work that are 80#.
Go to an auto supply store and ask for some “engine restore”, change your oil, and add. It SHOULD help.
 

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You also have to take the gauge itself into account, since three are the same the gauge my be reading low. If you don't want to spend money at first, swap coil and spark plug from a non misfiring cylinder. Also if the plug that came out of that low cylinder was not fouled, meaning unburnt oil, it should be firing, so try swapping the coils first.
 
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