1999 Buick Regal P0303 and P0171 Codes: Misfire and Lean Mix Issue After Plug and Injector Replacement

Model: 99 Buick Regal Fault Code: P0171 Posted: 2007-12-26 20:18

I'm completely stuck with my supercharged 1999 Buick Regal. The vehicle is experiencing a misfire and has stored both P0303 (cylinder 3 misfire) and P0171 (system lean condition) diagnostic trouble codes. I've already replaced all spark plugs and ignition wires, the #3 fuel injector, and swapped the coil pack coils to test if the issue moves to another cylinder. No vacuum leaks have been detected during inspection. Despite these efforts, the problem persists. Any insights or troubleshooting steps for this specific combination of codes in a supercharged 1999 Buick Regal would be greatly appreciated.