Replaced transition assembly. Performed furnace clean and tune; removed and cleaned burners along with the flame sensor did find a couple spots chipped in the flame sensor, I ohmed out the igniter and that tested week, I then did a powder test on the heat exchanger and did get blow back from left cell I removed coil patch to get a better look at the heat exchanger and did find a large amount of rust on that left side but no crack, I then cycled the system on and ran a combustion test verifying no CO in the airstream, lastly I came across a section of exhaust that was not glued I glued this section to prevent any issues. I recommend replacement on both the igniter and flame sensor. This sytem is currently operating normal at this time job complete