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post #1 of 2 (permalink) Old 11-29-2018, 01:48 AM Thread Starter
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Misfiring issue

Hello, I'm having a hard time finding out what's up with this thing first cobalt I've owned. So I'm not sure what common problems they have and if this is one. But I bought the car at a dealership about 2 months ago and it had a check engine light. Obd said cam shaft position sensors (already changed and fixed) that's what I thought would be causing the misfire. Did not. Also had system to lean thats because I think it has no pre cat o2 sensor... Not sure because of the engine? It's a 07 2.4 ss le5 I believe It should have the one. But again I'm new to cobalts. And I've never owned a car over a 98.

After I changed the cam shaft position sensors. This codes went away. Still have cylinder 2 misfire. Low voltage o2 sensor bank 1? Again there's not one and when I say that, like nothing no olet in header before the cat no wire no nothing. Has one after the cat and no where else. I did some searching for where I could be and what I assume where it should be was about 8 to 10 inches after the exhaust flange off the motor before the cat. And again there is nothing there at all. So that's a problem and I'm thinking that because of that it could be leaning out. Yesterday I changed all the spark plugs and the coil on number 2. Messed with the wires and made sure it had good connections. Cleared the codes and unplugged the negative on the battery. Drove it around a bit, ran good. I couldn't drive it enough fow the check engine light to come back on. Later I get in it to go to work. Its back on. low and behold cylinder 2 misfire.

When I changed the spark plugs they were black like it was running lean and burning oil. I didn't test the other coil by switching it, I just replaced it with a new one. All oem stuff.

I'm getting some other codes I can't remember them off the top of my head. Nothing serious like though. Next thing I would like to think is fuel issue? Obviously fixing the o2 sensor thing would be a help but I do not have the means or patience to do I by myself. And I have to drive the car every about 40 miles one way to work and back.

Now I've talked to the dealer about it and they seem at least willing to help me out with the repairs because I had stressed the issues when I bought the car.

Does anyone have any idea of what I need to do next? Has someone else ever seen or had this problem before? I'm thinking before fuel stuff, I'm going to try a compression test on cylinder 2. Just to make sure I have ruled that out. Any help would be greatly appreciated
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post #2 of 2 (permalink) Old 11-29-2018, 06:03 AM
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Firstly I've never seen an ecotec run on only 1 HO sensor unless tuned out. Looks like somebody canabalized the exhaust. HOs run in pair because the ECM compares the second to the first to trim fuel mixture. If you lean out an engine it is going to misfire on it's weakest cylinder.

I think you have to straighten this issue before you can move forward to a great life with your Cobalt. Treat it right and it will do the same.

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