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OK, so I've had this issue for the past 4 months. The check engine light comes on and stays solid. Car never even stalls. It shakes sometimes while stopped. I bring it to the mechanic, he hooks up the code reader and it comes up as cylinder 3 misfire. At first I thought it was just a hiccup since it first happened when the temperature dropped. It went out after a few days, and had been going on and off intermittently for a couple months. He then changed the spark plugs and the coils. It was out for a week and then came back on. He changed the coils a second time, and it came back on later in the day I picked it up. He then suggested getting some sea foam to put in the gas tank to clear it out. I put some in, drove it for a full tank of gas and it still wouldn't go out. I bring it to him and he turned it off with the code reader. Drove what totaled up to be close to another 400 miles with it being out. Then it comes back on again. So now I brought it back to him yesterday to change the injector. He said it cannot be the engine if I'm driving 400 miles with it out and it doesn't flash and not a stall even once, and that it is most likely something with the fuel system. So I get it today and he changed the injector, and said it was extremely dirty in there and recomended I keep putting more sea foam in the tank every few times I fill up. Drove another 50 miles and it came back on again! Only this time it came back on when I hit the gas and it jumped into the next gear, which it does sometimes. He mentioned that after he scrubbed it clean, it blew out a big cloud of smoke. Could it just be at this point that it needs more cleaning with the sea foam or is it an even bigger problem?
Given what you said, and assuming the check engine light is always a "misfire cylinder 3" code, I'm suspecting you may have some issues with that cylinder such as oil leaking from a bad valve seal and fouling the plug.
Tough to really confirm without inspecting the spark plug, but the fact that the problem comes back after some time has passed suggests it's a slow oil leak which needs time to begin to foul the plug up.
Given that your mechanic has changed the plug, two coils and injector and you are still having the issue, I'd do a compression test here, and reinspect the plug looking for signs of oil fouling it.
The comment "it's dirty in there" also makes me suspect oil, and running sea foam really isn't going to address the problem. Just a bandaid. I'd discontinue the sea foam.
What vehicle is this? What engine type/size and how many miles are on the engine?
Given what you said, and assuming the check engine light is always a "misfire cylinder 3" code, I'm suspecting you may have some issues with that cylinder such as oil leaking from a bad valve seal and fouling the plug.
Tough to really confirm without inspecting the spark plug, but the fact that the problem comes back after some time has passed suggests it's a slow oil leak which needs time to begin to foul the plug up.
Given that your mechanic has changed the plug, two coils and injector and you are still having the issue, I'd do a compression test here, and reinspect the plug looking for signs of oil fouling it.
The comment "it's dirty in there" also makes me suspect oil, and running sea foam really isn't going to address the problem. Just a bandaid. I'd discontinue the sea foam.
What vehicle is this? What engine type/size and how many miles are on the engine?
It's a 2010 Chevy Cobalt. 4 cylinder engine. 84,000 miles. Got it in July 2015 it had 36,000 miles, I put the rest on. I have been taking care of it pretty thoroughly. They also checked for leaks the first time I brought it in and could not find any.
I agree with BostonMike. There is something wrong with the engine.
About the only way to find it that I know of short of a tear-down would require testing. Compression test may show something, but a leak down test is better.
And even then you may not find the problem. Might have to pull the head.
I agree with BostonMike. There is something wrong with the engine.
About the only way to find it that I know of short of a tear-down would require testing. Compression test may show something, but a leak down test is better.
And even then you may not find the problem. Might have to pull the head.
Be kinda sad if they pull the head and then figure out it is a loose wire.
I think you need a better mechanic. He's looking at the parts not us. I mean, "dirty sparkplug": they can be dirty in a few different ways. Covered in oil, or covered in soot. One indicates oil usage, the other running rich. [Could be covered in raw gas too, but that seems unlikely in this case.]
Throwing plugs, then coils at this does seem logical, I can't blame that. I'm not a fan of Seafoam but tossing injector cleaners in, ok. Bad injector? It happens. But at this point something else seems to be the problem.
OK, so I've had this issue for the past 4 months. The check engine light comes on and stays solid. Car never even stalls. It shakes sometimes while stopped. I bring it to the mechanic, he hooks up the code reader and it comes up as cylinder 3 misfire. At first I thought it was just a hiccup since it first happened when the temperature dropped. It went out after a few days, and had been going on and off intermittently for a couple months. He then changed the spark plugs and the coils. It was out for a week and then came back on. He changed the coils a second time, and it came back on later in the day I picked it up. He then suggested getting some sea foam to put in the gas tank to clear it out. I put some in, drove it for a full tank of gas and it still wouldn't go out. I bring it to him and he turned it off with the code reader. Drove what totaled up to be close to another 400 miles with it being out. Then it comes back on again. So now I brought it back to him yesterday to change the injector. He said it cannot be the engine if I'm driving 400 miles with it out and it doesn't flash and not a stall even once, and that it is most likely something with the fuel system. So I get it today and he changed the injector, and said it was extremely dirty in there and recomended I keep putting more sea foam in the tank every few times I fill up. Drove another 50 miles and it came back on again! Only this time it came back on when I hit the gas and it jumped into the next gear, which it does sometimes. He mentioned that after he scrubbed it clean, it blew out a big cloud of smoke. Could it just be at this point that it needs more cleaning with the sea foam or is it an even bigger problem?
Do a google search on your actual check engine code in a Chevy Cobalt forum, im pretty much you are not the only one who has had this issue and you will probably find a cause and actual fix for it there.
Could be something minor like a gas cap, cracked piece of rubbed, or something major in the making.
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