Performed furnace safety check; I cycled the system on and first performed a powder test on the heat exchanger and did receive blowback from all 3 cells, I then ohmed out the igniter, lastly performed a combustion test and did get high levels of CO and excess air in the exhaust. At this point this system is unsafe for operation. Due to age, condition, and cost to repair replacement of the system is recommended. Job complete second opinion scheduled with Dan F