Vehicle: 2008 Ford F-350 Super Duty, 2WD, V10-6.8L, Automatic Transmission
Problem: The truck hesitates and bogs on acceleration. Malfunction Indicator Light is on.
Details: : The tech pulled Diagnostic Trouble Codes P0306 and P0420. Checking PIDs with a scan tool, he found that the Fuel Trim adjustments (long- and short-term fuel trims combined) were Bank 1 = -7% and Bank 2 = +22%. He conducted an exhaust back pressure test on both banks and found high back pressure on Bank 1.
Confirmed Repair: Based on his findings, the tech concluded that since this truck had a converter on each bank, when one bank was restricted, no fresh air from intake went into that bank, causing the fuel trims to go negative. All the fresh air went into the other bank, causing the mixture to go lean and fuel trims to go positive. They tech found the catalytic converter was plugged. He replaced it and cleared the DTCs. The truck now runs normally.