2003 Chevrolet Silverado 1500 4.3L V6: P0172 and P0300 Codes - Engine Stumbles, Shakes at High Speed
I own a 2003 Chevrolet Silverado 1500 with a 4.3L V6 engine and automatic transmission. The OBDII check engine light activated while I was driving at 35-40 mph. After that, the vehicle began to stumble and shake noticeably. The light started blinking, which stopped only when I reduced my speed to about 15-20 mph. Every time I attempted to accelerate beyond 40-45 mph, the engine would stutter, shake, and the check engine light would blink again. During acceleration, I noticed inconsistent power delivery—sometimes a sudden drop in performance, followed by an abrupt surge. Initially, the only code displayed was P0300 (random misfire). I replaced the ACDELCO spark plugs and ignition cables. After driving a few miles, the vehicle seemed to run normally, but the next day the symptoms returned. Now, both P0172 (fuel trim bank 1 too rich) and P0300 are present. Additional details: Last year, I had new catalytic converters and oxygen sensors installed. I'm seeking advice on how to diagnose and resolve these issues effectively.
My two cents: A flashing check engine light (CEL/SES) is a serious warning—potential damage to the catalytic converter is likely. Most common causes involve excess fuel, such as a leaking fuel injector or a faulty fuel pressure regulator. Your codes indicate P0300 (random misfire) and P0172 (running rich on bank 1). To begin troubleshooting: - Use a fuel pressure gauge to measure overall fuel pressure. Check for proper pressure and perform a leak-down test—how quickly does the pressure drop after turning off the key? - Inspect the vacuum line connected to the fuel pressure regulator—there should be no fuel present. - Remove and inspect spark plugs, especially on bank 1, looking for wetness, dryness, black or tan deposits to identify potential faulty injectors. If you have an OBD2 scanner, check freeze frame data for key operating conditions. Always share additional details: other issues, existing codes, modifications, or use of aftermarket parts.