1997 Chevrolet C1500 4.3L Manual Transmission P0300 Misfire - Cold Weather Hesitation After Replacing All Spark Components
My 1997 Chevrolet C1500 with a 4.3L V6 manual transmission is throwing a P0300 code indicating multiple cylinder misfires. The truck runs smoothly in neutral and can rev up to 2000 RPM without issues, but when driving at around 2000 RPM, it begins to hesitate noticeably. This issue worsens under cool outdoor temperatures. I've already replaced the distributor, coil, spark plugs, ignition cables, mass air sensor, intake air sensor, cam position sensor, and crankshaft position sensor. All components were tested using a digital multimeter (DMM) according to the factory manual, yet no root cause has been identified. The misfire seems to be intermittent and temperature-dependent. I'm now seeking advice on potential underlying causes beyond ignition system failures.
Check fuel pressure first, then perform a KOEO (Key On, Engine Off) test to observe any pressure drop—ideally, it should not drop more than X psi within five minutes. Also verify the ECT (Engine Coolant Temperature) sensor reading using an OBD2 scanner. Ensure there are no additional diagnostic trouble codes (DTCs) stored in the ECM.