Engine Backfires (Lean Fuel Mixture)
- Check for vacuum leaks (oil filler cap, oil dipstick, hose connections, PCV hose, PCV valve and EGR system).
- Check idle speed and ensure ignition timing is correct.
- Check airflow meter, coolant temperature sensor, throttle position sensor and air temperature sensor.
- Check cold start injector and cold start injector time switch.
- Ensure fuel system functions properly (pump, lines, filter and pressure regulator).
- Check for clogged fuel injectors.
- Check power to ECU via fusible links, fuses and EFI main relay.
- Check injection signal circuit.
- Check O2 sensor(s).