3rd Cylinder Misfire. PLEASE HELP

[MrLegit827]

Hello everyone, I have a 2006 Chevy Cobalt LT coupe. I love these cars because of how great they run when working properly, but am also aware of the many infamous problems they have.

I have a 3rd cylinder misfire on mine, and I've done a lot to it to try and fix it but no luck. All the cylinders run at 160 except the 3rd one (120). It only misfires at stops or in idle, other than that, runs beautiful.

I've replaced all the plugs, coil pack rail, used steel seal to fix any potential cracks running through the motor, used marvel mystery oil, guaranteed to pass, resolve (compression booster), and even used spray to fix electrical connections. I'm almost certain the fuel injectors are fine and throttle body are fine as well

I am at the point where im around 90% SURE it is electrical, is it the ICM? ECM? Do i need a new harness? etc, I don't know what to do, help please!!!!!!

 

[YelloEye]

Checked your valves?

 

[MrLegit827]

I haven't taken the head off yet, I didn't want to take it apart yet. For some reason I'm thinking it is possibly a faulty ignition control module? Because the car has had a few failed and hesitant starts, and I know an improper working ICM can cause that and also a misfire in the engine

 

[YelloEye]

Same goes for the valves. Did you do a leak down when you did the pressure test?

 

[onedoughboy]

The 120 pounds on the number 3 cylinder is most likely the problem. Valve or rings, not electrical. Most manuals state there should be no more then 10 psi difference between cylinders. There are two coils, each coil fires two spark plugs at the same time, one with fuel and another without. If this were your problem, you would have a misfire on two cylinders. The cylinder with fuel and compressed air, has less resistance and will have more spark. You may want to try a different spark plug in number 3, one of those hotter, multi prong special alloys plugs, might lesson the number of misfires. You may also want to have your injectors checked, flow tested to make sure they are working properly.

 

[ThoR294]

The 120 pounds on the number 3 cylinder is most likely the problem. Valve or rings, not electrical. Most manuals state there should be no more then 10 psi difference between cylinders. There are two coils, each coil fires two spark plugs at the same time, one with fuel and another without. If this were your problem, you would have a misfire on two cylinders. The cylinder with fuel and compressed air, has less resistance and will have more spark. You may want to try a different spark plug in number 3, one of those hotter, multi prong special alloys plugs, might lesson the number of misfires. You may also want to have your injectors checked, flow tested to make sure they are working properly.

+1 to compression issue. find out why it is not squeezing as much as the rest

 

[NovaScotiaLS]

Maybe try a wet compression test, that will tell you if the low compression is rings or valve related

 

[MrLegit827]

I will try a wet compression test thank you NovaScotiaLS, and also I'll try cleaning and checking the injectors but the way my cobalt is, there aren't two coil packs. Its an ecotec 2.2 and the coil is 1 whole rail that goes across each cylinder. If it comes down to it ill definately ccheck the valve I have just been convinced its electrical related. Think if I get a certain type a plug like you said I can get my compression boosted so the mis goes away? Thanks again guys

 

[YelloEye]

A special plug won't fix a compression issue. You can get them to run hotter or colder, but that's it.

 

[MrLegit827]

Ok gotcha, later I'm going to check the fuel injector and also I'm going to keep treating it with special ring/valve repair. A mechanic told me pouring brake fluid "cleans all the shit out of there" and lately the engine light has been coming and going so my misfire has been inconsistent which is good because I am definitely seeing some results but I know it's still there, just not as bad. Thanks again