Po3o3 3rd Cylinder Misfire - Chevy Cobalt Forum / Cobalt Reviews / Cobalt SS / Cobalt Parts
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post #1 of 7 (permalink) Old 12-29-2012, 08:43 AM Thread Starter
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Po3o3 3rd Cylinder Misfire


Disclaimer: I am not very car savvy, but I can grasp things that are explained to me pretty quickly.

I recently (about 1 year ago) bought a 2007 Chevy Cobalt LS 4-door 2.2 engine with about 55,000 miles on it. Recently the check engine light came on and I used a code reader to get the reading. It came out as a P0303 error which I researched and found out is a misfire on the 3rd cylinder.

I first tried to replace the spark plugs (with ACdelco's per the recommendations i had read). That did not fix the issue so I brought it in to my local mechanic who changed the coil (did not work) and then the fuel injector (also did not work).

He then brought it to his sister shop with the more advanced diagnostics and took a pressure reading. The other three cylinders were showing up as normal with 140 lbs(?) while the third cylinder was reading only 70. He then recommended me to a different mechanic that does "deep engine work".

This new mechanic told me that it was most likely carbon build up in the cylinders and to put a cleaning agent in the fuel and "drive the piss out of it" and it would clear the issue up. We put the cleaner in, drove a couple hundred miles then reset the computer and drove another 50 miles before the light came back on (this was better than the 5 miles each previous "solution" worked for).

What should my next steps be? I'm working with a budget and can't keep dishing out for these "solutions" that don't work. Is the cleaning solution working and I just need to add more and keep driving it? My mechanic mentioned finding someone to use a a specific machine to clean the carbon out, is tat worth looking into, or is it time to take it into the dealer, pay whatever exorbitant diagnostic fee they have and accept their answer as the solution?

Thank you for your help!
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post #2 of 7 (permalink) Old 12-29-2012, 08:57 AM
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Dealer is definitely not the answer, if its just build up use some sea foam in the gas tank. And or fuel system cleaner.

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post #3 of 7 (permalink) Old 12-29-2012, 09:16 AM
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Get an other compression test to see if the last solution helped, if you're up to 90 then you know to continue for a bit more.

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post #4 of 7 (permalink) Old 12-29-2012, 03:28 PM
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Welcome to the forum! We have some top-notch, technically savvy folks who are already chiming in (unfortunatley, I'm not technically trained and so cannot contribute in that way). If you do decide to work with a dealership, please keep me posted as I'm available to work with you through that process if you like.

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post #5 of 7 (permalink) Old 12-31-2012, 01:17 PM
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I really hate to say this, but take it to the dealer. I know a lot of people on here (myself included a few years ago) are gung-ho against dealer wrenches, but I'm going to give you my reason why.

Back in late 2009 or early 2010, my 06 Cobalt LT threw a code. My hubby is a body guy, so he took it to a wrench friend of his to get the code read without paying a $50+ diagnostic fee. (My hubby's OBD reader hasn't been updated and couldn't get a read off of it, or he'd have done it himself.) It was the code for the throttle position sensor. It had been stalling out at low idle before the code was thrown. Wrench said to ride it out. Few wks later it came back, and we replaced the throttle body. Still stalled out. To make a long story super short, over the next 2 years, she developed a misfire (a SHAKING misfire at times). We changed plugs 2x (once with autolites, once with AC Delcos), tried dry gas, 2 diff. kinds of injection cleaner, new injectors (which, if anyone ever needs them, Chevy did have a set of 4 for about $100 instead of $100 each!), AND a new coil pack. I also started running Shell premium (already ran shell, just used regular) gas. Nothing. Where is this car today? Sitting parked at my husband's shop. She's still being paid on, and we're leasing a 2012 CRV. When you start her up, she's louder than the 73 IH pickup my hubby just restored.

My mom had the same code pop up on her 05 LS. Lucky bitch (and I say this nicely - she is my mom after all!) was still under factory warranty, since she bought the thing new and had it extended to 7 years. The code popped on a Sun, took it to autozone to have it read (throttle position sensor), and by Mon, it was in the hands of the local GM wrench. They replaced the throttle body, and she has had no problems since.

Now, I don't know for sure that me "waiting it out" caused more problems, or not. Hard to say. My code first threw around 63k miles. My mom's threw around the same time, just 2 years later. (She's 62, and doesn't drive much other than to work and back. Maybe a trip to Indiana or TN from Ohio to see family every once in a while, but that's it.) I'll be honest, though. Even though I LOVE the CRV, had I known that paying a little more and taking it to GM might have cured the problem, hindsight says that we should've bit the bullet and done it, especially since we're paying on a vehicle that's not even drivable!
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post #6 of 7 (permalink) Old 12-31-2012, 03:13 PM
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Take the car and hit it into a pole. Insurance covers it and problem is solved.

That's directed at the post directly above mine

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post #7 of 7 (permalink) Old 01-04-2013, 03:44 AM
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Originally Posted by money_man View Post
Take the car and hit it into a pole. Insurance covers it and problem is solved.

That's directed at the post directly above mine
LOL I would, but I don't know that the knock in the engine would last long enough to even do so!! As it is, hubby and I have already decided that the next hail storm that comes along, we're going to trailer the balt and follow the storm!! Now I just need a hail storm BEFORE I finish paying it off. I'm upside down in the loan, but ONLY because of the engine probs. I have the gap insurance on it, though, so a total out wouldn't bother me. Trust me, I've thought of stuff like this before! Even when I hear that there's been some sort of crime in our small town, I cross my fingers that it involves a baseball bat and the cobalt.
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