1997 Chevrolet Silverado P0305 and P0300 Misfire Diagnosis - Fuel or Ignition Issue?
This is my first time posting on the forum, so I'm hoping for some expert advice. I have a 1997 Chevrolet Silverado K1500 4x4 with a 5.7L engine. Last weekend, I replaced the fuel tank, installed new fuel lines (halfway to the engine), a new fuel filter (both supply and return), and a new sending unit. The truck ran smoothly before all these upgrades. After reassembly, I started it up — it fired right up, but the check engine light began flashing. A scan tool revealed two codes: P0305 (misfire in cylinder 5) and P0300 (random misfires). I haven't replaced the spark plugs yet, though I did install new spark plug wires and a distributor cap. The issue seems to be related to ignition or fuel delivery. Could this be due to something simple like a defective distributor cap? Or is there another underlying cause? Any guidance on how to troubleshoot this step-by-step would be greatly appreciated.
P0305 indicates a misfire in cylinder 5. P0300 suggests random or multiple cylinder misfires. Possible causes: 1. Ignition system: spark plugs, wires, coil packs 2. Fuel delivery: injectors, fuel pressure, clogged or stuck injectors 3. Mechanical issues: compression loss, vacuum leaks Recommended steps: - Check if the spark plug is firing — use a noid light to verify injector pulsing. - Inspect spark plugs for fouling (black or wet deposits); use only AC Delco plugs. - Test fuel pressure; with the engine off, check pressure and observe any drop over 5 minutes under KOEO conditions. Start by ruling out ignition and fuel issues. If those are fine, proceed to compression testing and vacuum leak checks — these are common culprits in misfires. The flashing check engine light points strongly toward an ignition or fuel system problem.