The dreaded misfire

I have a 2011 Aveo Lt. Check engine light came on with a cylinder 1 misfire. It needed a tune up anyway so I replaced the plugs and coil pack. Within a day misfire was back but different cylinder. Took coil back and got a new one. It was fine for a few months then misfire came back and running so rough I gave up and took it to a mechanic. He decided the coil was bad and replaced it with my warranty. It ran fine for a month and misfire again. This time I decided to replace the valve cover gasket because of all the oil accumulating around the plugs, changed the plugs again, and replaced the coil once again. Started up, ran smooth, cleared codes. Drove it quarter mile down road and check engine light started flashing but went off when I let off the throttle. Turned around the go home, check engine light started flashing again and had a miss. Got home, check engine light was off again but was still showing misfire code again. This is the 5th coil in 8 months that has been in the car, 3rd set of plugs. When I had it in the mechanics garage he checked compression and the injectors and said that was fine. What else could this be? Anyone have a clue? I sure don't anymore.

I don't know for sure. But my favorite go-to Bad Guy for strange problems on 2009-2011 Aveos is the wiring harness to chassis ground connections near the underhood ECM, and also near the starter. If I recall correctly, the 2009-2011 USA/Canada 1.6 litre Aveos, and 1.8 litre Cruzes in the USA/Canada also have a "waste spark" type coil. I'm just guessing, but a bad connection somewhere, or grounding problem, might be a possible suspect.

Deano

You have just described the past couple of years of ownership with my 09 Aveo5. I was really hoping there would be some more ideas in this thread after I read the original post. The misfires were so bad on mine they melted the insides of my catalytic converters, so we broke them up so the exhaust goes through nothing and I now have o2 sensor errors as expected. Luckily WI doesn't have inspections.