Upon inspection found heat exchanger cracked with high levels of carbon monoxide as much as 156PPMs . Per AGA ( American gas association ) the only two options given to fix this issue are replacement of the heat exchanger or replacement of the furnace. Also found gas pressures not regulated per manufacturer specs at manifold pressures is 4.00inWC , Manufacturer requirements are 3.0-3.8 max at manifold. Upon further inspection found p trap without overflow safety, no secondary overflow safety as well as the drain line installed incorrectly per manufacturer specs . Build and presented estimate to customer, customer accepted estimate for the heat exchanger replacement at this time.