2006 Cobalt 2.2L misfire

[dakotart]

Backgroud: 2006 Cobalt 2.2L

 

Back in December 2018 - Previous issue: Leaking/bent valves - this car got a new head, timing chain, water pump, etc.

 

Car doesn't get driven very much since then but starting around March I was told it wasn't running right. Was told that after driving it for awhile, it would start running fine. No misfire, engine running smooth.

 

As of today:

Codes: P0301 (misfire cylinder 1); P0171 (Bank 1 system too lean)

 

Drove car to my house and pulled plugs. Cyl 1 plug was wet.

 

Compression test: Cyl 1 = 30psi; Cyl 2-4 190-200 psi

 

Leak down test (if I did it correctly); Pressurize cylinder and can hear air leading from dip stick tube and valve cover hose that goes to air filter tube).

Harbor Freight leak down tester says Cyl 1 = 100% loss; Cyl 2-4 are in the red for loss - 80% I think). This indicates issue is with the rings.

 

Looking for ideas as it doesn't make sense to me that this issue resolves itself if driven for a distance.

[Cordell]

Things expand and seal up better when hot, certainly could be rings. Hard to say without tearing it down at this point. You’ve proven a mechanical issue with cylinder 1, unless you just want to put an engine in it all you can do is pop the piston out and look.

[Geeto67]

Something I have seen in motorcycles but not really in cars, is that when they sit for a while the rings will stick inside the piston groves. This will cause a low compression situation but will usually free up after heat cycling, only to happen again once it sits. usually this also means blow by of gas into the oil, pull the dipstick and see if it stinks of gasoline.

 

Scott is 100% spot on though - all you can do is pull the piston out and inspect the rings and cylinder wall. you could also try driving it regularly and see if it clears up on it's own.