I have a 6890N GC with dual FID. The back column has a much higher flow rate than the front column. The two columns are identical and the setup for inlet, column and detector are identical. I have also swapped the EPC's between the two detectors. Seems no matter what I do the flow is much higher on the back column than the front column as evidenced by very short retention times and at least 3X higher readings on a flow meter. The pressures displayed on the GC all look normal! I know the flow on the front column is correct as the retention times match well with prior data on this GC and is a good match with other GC's we have in the department. Is there a component that can fail and cause higher flow rates without an indication of higher pressure on the front panel?