1998 Chevy C-1500 P0300 Code: Random Multiple Cylinder Misfire and Hard Starting Solutions

Fuel system is the most likely culprit, though some aftermarket spark plug caps are known to perform poorly and contribute to misfires.

I recommend checking both ignition and fuel systems. The CPI (Common Rail) injection system in older 5.7L Vortec engines is notorious for causing intermittent misfires. Using a proper scan tool, you can test injector actuation and perform a fuel leak-down test. I've replaced several of these CPI injectors due to recurring missing issues. A aftermarket spider injector kit that relocates injectors directly to intake ports instead of the CPI unit may resolve this problem.

I have a 1997 Chevy C-1500 with the same symptoms, but it's equipped with a throttle body injection system on the 5.7L Vortec engine. The vehicle has over 180,000 miles and all ignition components are less than 10,000 miles old. This issue is frustrating and costly to diagnose and repair. Any advice would be greatly appreciated.