Chopper8176
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Yup, papa Karl suggested the compression test, so pressure test it will be.
Cylinder 1 Misfire, please help
- Thread starter jan_mast
- Start date
All,
I forgot to update this threat with teh fix.
The local repair guys wanted me to replace all the coil packs. I called bullshit on this because i tried swapping the coil pack and the fault code stayed on the #1 cylinder. I then took the car to teh dealership. They did a compression test and found that #1 cylinder was much lower PSI than the other cylinders. They wanted more than $1,000 to tear off teh head and figure out why the pressure was low.
I said no thanks and bought the factory service manuals, best $250 i ever spent! Between the book and online forums i determined that the most likely culprits were: valves, piston rings, or head gasket.
After pulling the head assembly off inspection of the valves showed blow by on one of the valves, meaning it wasnt closing properly. Since i was in there i replaced the valves, springs, and associated hardware for all 4 valves in that cylinder. I also replaced the head gasket and vale cover gasket too. After replacing the valves, i stacked up the springs side by side, and alas the one with blow by was shorter than then other 3. The spring had failed.
Replacing the valves was childs play with a spring compressor. By far the hardest part was re-timing the engine, which i figured out a clever way to do. If you all have any more questions, let me know, ill walk you through what i did. The dealership would have charged me more than $3,000 for this repair. I did it for $400 (including the cost of the service manuals). Total time spent, about 12 hours, because i am a fucking noob mechanic. Good luck all.
I forgot to update this threat with teh fix.
The local repair guys wanted me to replace all the coil packs. I called bullshit on this because i tried swapping the coil pack and the fault code stayed on the #1 cylinder. I then took the car to teh dealership. They did a compression test and found that #1 cylinder was much lower PSI than the other cylinders. They wanted more than $1,000 to tear off teh head and figure out why the pressure was low.
I said no thanks and bought the factory service manuals, best $250 i ever spent! Between the book and online forums i determined that the most likely culprits were: valves, piston rings, or head gasket.
After pulling the head assembly off inspection of the valves showed blow by on one of the valves, meaning it wasnt closing properly. Since i was in there i replaced the valves, springs, and associated hardware for all 4 valves in that cylinder. I also replaced the head gasket and vale cover gasket too. After replacing the valves, i stacked up the springs side by side, and alas the one with blow by was shorter than then other 3. The spring had failed.
Replacing the valves was childs play with a spring compressor. By far the hardest part was re-timing the engine, which i figured out a clever way to do. If you all have any more questions, let me know, ill walk you through what i did. The dealership would have charged me more than $3,000 for this repair. I did it for $400 (including the cost of the service manuals). Total time spent, about 12 hours, because i am a fucking noob mechanic. Good luck all.
Chopper8176
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That might be exactly the problem, when I took off the air duct work to throttle body. I flipped it open with a bright light I seen what looked like oil drip in there and it smelled of motor oil. The compression test was my next step. Thanks a bunch for posting your outcome
Timing is easy, just gotta line up the colored links.
Chopper8176
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Well, compression test results were identical. Became up with 110 psi in each cylinder. Engine light hasn't been for a while. I go over a mountain every other day. It usually comes on as I am going up, will see if it comes on today, on my way back
It sounds like you have a weak valve spring at this point. The next step is to perform a cylinder leak down test on the cylinder that has the misfire. You have to remove the camshafts, or at least lift them up enough so the valves are all in the up position. Attach the pressure hose and gauge and fill the cylinder with compressed air. If you notice a drop in pressure fairly quickly, this means a valve is bad. You can listen to the intake and exhaust for a leak. If there is no leak, this is an indication of a weak valve spring. This is not too painful of a job.
Chopper8176
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Never got around to do the leak down test. I did do a coolant pressure test, that passed. I noticed when i give the gas pedal a hard but quick push. It sounds almost like i have a CAI (sucking or harsh blowing), i have stock air box with drop in k&n filter. I have yet to trace down the sound. When i try to listen close, looks as if TB or intake man. Car hesitates, doesn't want to exceed 4k rpm's. I'll take off air intake duct, see if i can narrow down that sound.
I did spray carb cleaner around parts of the intake manifold and TB i could access at the time. Then i stopped, thinking i have a hundred miles to drive, i don't want the engine catching fire.
Also, when i fire up the car when it after it sits for a couple hours or more, a heavy tapping comes on for about 3 seconds, then it goes away. Changed purge valve as well, with n I results.
I did spray carb cleaner around parts of the intake manifold and TB i could access at the time. Then i stopped, thinking i have a hundred miles to drive, i don't want the engine catching fire.
Also, when i fire up the car when it after it sits for a couple hours or more, a heavy tapping comes on for about 3 seconds, then it goes away. Changed purge valve as well, with n I results.
Last edited:
Michael DY
Junior Member
Hi, my name is Michael I'm new here and I've purchased a 2010 cobalt from Craigslist today and it ended up having a misfire long story short I did a compression test and cylinder 1 had lower psi then the rest of the cyclinders it read 60 psi the rest were around 150 psi , now I invested the majority of my money on This vehicle so now I must fix it I'm no stranger to tools and I do basic mechanic work but I'm up for the challenge that you have accomplished can you please help me and walk me through it I'm invested in this project . Thank you in advance really would appretiate the help !
Michael, I assume you did a dry compression test. I see that it failed. Did you do a wet compression test on that cylinder? Basically you squirt some oil down in the spark plug opening, recommend the test gauge and run that compression test.
Basically when you have a loss of compression you can narrow it down to a list of culprits: head gasket, valve, spring, piston rings.
I have done two valve jobs on my cobalt in two years. The first time it was a failed valve spring. Tore the valve head off and inspected the #1 cylinder. Saw blow by on one of valves. So clearly the valve wasn't seating fully, this the blow by, and loss of compression. Changed all 4 valves and springs. Stacked all the springs next to each other and the one was visibly shorter than the other two.
The hardest part of the whole evolution was re-timing, which was lining up timing marks on the crank shaft and can shafts. Feel free to email me if you like [email protected]
Basically when you have a loss of compression you can narrow it down to a list of culprits: head gasket, valve, spring, piston rings.
I have done two valve jobs on my cobalt in two years. The first time it was a failed valve spring. Tore the valve head off and inspected the #1 cylinder. Saw blow by on one of valves. So clearly the valve wasn't seating fully, this the blow by, and loss of compression. Changed all 4 valves and springs. Stacked all the springs next to each other and the one was visibly shorter than the other two.
The hardest part of the whole evolution was re-timing, which was lining up timing marks on the crank shaft and can shafts. Feel free to email me if you like [email protected]
