Misfire help please!

[Brokenraven]

I am having big trouble with my 2010 gmc sierra 5.3. It started 1 day driving home stabilatrack came on truck ran really rough. Took it to autozone to have the codes read it was a p0306 i also have a oil sensor code that has been there for some time. Also a throttle pedal position sensor wich instead they sold me a throttle position sensor i changed for no reason. 2 years ago i had the same misfire but on 1 it was a smoked spark plug so i was assuming that was it again but it wasnt. So far i have changed the plugs on 6 twice. swapped coils and wires to see if the code chased. Listened to injector to see if it was firing it was. Did a compression check on that side of motor all were at 145 except 6 wich was 115. So next step i pulled valve cover to see if the afm lifter is collapsed and the rockers were tight and all of them move on crank. No issues. Does anyone have any other ideas? Also the spark plug on 6 smelled of gas when i pullled it. The exhaust smells of fuel as well. Truck has been sitting for 2 months now. Thanks for any help!

[CamGTP]

Cylinder 6 being at only 115psi is pretty bad compared to the others.

 

Have you done a leak down test yet?

[Brokenraven]

Thanks for the reply. I have not done a leak down test yet. 

[swathdiver]

Stuck or leaky injector wiped out cylinder walls which is causing blow by, probably have gas in oil.  Once this is all fixed, expect the cat(s) to fail; see it all the time on here.

 

You might get by with pulling piston and rod out of that cylinder, honing it out and putting new rings on piston if still good.  Before doing that, I would test full functionality of AFM system with scan tool and do leakdown test.

[Brokenraven]

Damn i was hoping it would be something simple but i knew it wasnt going to be. That was the theory i was having today if it could be a injector and now its caused bigger problems.