P0304, Low Compression, 2009 2.2 - Chevy Cobalt Forum / Cobalt Reviews / Cobalt SS / Cobalt Parts
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post #1 of 2 (permalink) Old 09-04-2016, 06:05 PM Thread Starter
Join Date: Sep 2016
Posts: 6
P0304, Low Compression, 2009 2.2

Hey Y'all,

Looking for advice and tips, been reading thru the various reports on P0301 ~ 04 codes. Here is the deal with mama's little crusier. It is a very stock 2009 LS with the 2.2 ecotec, sitting about 105K. About six months back it started spiting a P0304 code, intermitantly. At 102K it started to set more frequently, so I replaced the plugs. That seam to help for about a week, then the code came back HARD. All this time it still runs smooth, fuel economy still good. Swapped the coil packs, with no effect, figured I would take it to the dealer, I didn't want to mess with the fuel injectors.

Dealer comes back with low compresion on #4, reading 30psi, rest are at 150psi. They immediately want to pull the head. I politely refused at that point, wanted to check my options. When I got to the dealership to pick it up, I asked the service writer if they had oiled the cylinder to eliminate the rings, he looked at me ilke I had grown a second head all of a sudden.

Long story short, I ran the compression test myself, along with a leakdown test. Found that the #4 exhaust valve are leaking. Found a great troubleshooting video here:

Remember this is a stock mom car, what do I need to think about on a head rebuild. A local shop I called quoted me 180 to run the head. Timing Chain? Thermostat? Any tips or tricks would be greatly appreciated. My last rebuild was 25+ years back. Thanks for reading!
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post #2 of 2 (permalink) Old 09-05-2016, 05:27 PM Thread Starter
Join Date: Sep 2016
Posts: 6
Heads off!

Getting the belt off this thing is a BEAR! Rent the special belt tool, even that didn't work. Hooked the tensioner and just pulled like hell.

Rest of the head pull was pretty straight forward. Drained the coolant, but still ended up filling the cylinders with the smelly pink stuff.

Confirmed #4 exhaust leaking. Did a bubble test like Ivan in the video, leaking like a sieve. Off to the machine shop...
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head r and r , low compression , misfire

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