2000 GMC Astro Van P0300 Misfire: Fuel Pump Replacement, Cap/Rotor Issues & Coil Diagnosis
At 135,000 miles, my 2000 GMC Astro Van experienced a fuel pump failure. The first replacement was an aftermarket O'Reilly unit, which immediately triggered a P0300 misfire code. After removing it and installing a genuine GM AC Delco fuel pump, the van ran smoothly until reaching 142,000 miles when the P0300 code returned. Since the vehicle has never had a tune-up, I replaced the spark plugs, distributor cap, rotor, and installed a new fuel filter. During this process, I discovered that the wiring harness for cylinders 2, 4, and 6 runs across the valve cover and was deteriorating—this likely contributed to intermittent misfires. The van ran well until approximately 144,000 miles when the P0300 code reappeared. I noticed a noticeable shuttering sensation at cruise speed (around 70 mph), along with activation of the SES light and P0300. After several drive cycles, the code would clear for a week before returning—now it sets within about 10 miles on the freeway during steady cruising. I am currently investigating the coil pack as a potential cause. Given that cylinders 2, 4, and 6 are not shielded where they cross the valve cover, I expect misfires to appear as P0302, P0304, or P0306 if wiring insulation is compromised. As part of my ongoing diagnostics, I am re-wrapping the 2-4-6 spark plug wires, inspecting the cap and rotor, and replacing them with factory OEM parts—specifically a GM AC Delco unit—to eliminate arcing issues common in aftermarket components. This issue highlights the importance of proper spark component quality in older Vortec-powered Astro vans.
A factory distributor cap is highly recommended for your 2000 Vortec-powered Astro Van. These engines, especially those with the 'cross-fire' cap design, are prone to internal arcing in cheaper aftermarket caps. If a dealer isn't accessible, consider using a Wells brand cap—known for reliability and better construction suited to this engine type. Also note that fuel pressure regulators can leak, causing misfires on one bank of cylinders. Additionally, grounding issues near the fuel pump connector or problems with EGR valves and exhaust converters at higher mileages may contribute to erratic performance. While coil packs are worth checking, start with replacing the cap as a primary step. Could you share your van's year and current mileage?