1996 Silverado 5.7L Vortec P0300 Misfire: Shaking at 65+ MPH and Flashing Check Engine Light
I own a 1996 Chevrolet Silverado with a 5.7L Vortec engine. When I drive over 65 mph, the truck shakes noticeably—similar to having a tire out of balance—and the check engine light flashes intermittently. A diagnostic scan shows a P0300 code indicating multiple cylinder misfires. The issue only occurs at higher speeds; driving in town or during city traffic is fine. This problem started about a few weeks ago. A year ago, I replaced the distributor, ignition coils, spark plugs, and plug wires—all new parts. Despite these upgrades, the issue has returned. I'm wondering if this could be related to fuel quality, sensor issues, or engine timing. Does anyone else have experienced this on a 1996 Silverado with a Vortec engine? Any suggestions for troubleshooting? Key details: - Vehicle: 1996 Chevrolet Silverado (5.7L Vortec) - Symptom: Shaking at speeds above 65 mph, flashing check engine light - Fault code: P030 T00 (Multiple Cylinder Misfire) - Previous repairs: New distributor, plugs, wires, ignition system
P0300 is a common diagnostic code, especially in older Vortec engines—many users report similar issues. A flashing check engine light strongly suggests potential damage to the catalytic converter, which may be linked to fuel quality or delivery problems. Are there any other related codes (e.g., P0171/P0174) present? Vehicle is stock? No modifications? Basic troubleshooting steps: - Perform a fuel pressure test using a gauge—please share the PSI reading. - After turning off the engine, observe how quickly fuel pressure drops—post your results. Additional questions: - Why were the distributor and ignition components replaced last year? - Were AC Delco spark plugs used? - What does 'new ignition' mean? Does it refer to the ignition coil or the ignition switch?