i have a 03 avalanche 5.3l , it started missing the other day, comes to find out, the 4 left cylinders have no combustion, they coils are firing, i thought my fuel rail was clogged, the mechanic said the rail was clear, any suggestions ?

 

found the problem, left cataletic converter was plugged up, hope this info will help someone else

 

I was thinking either that or the sensor on that side.