1. Faulty spark plugs or ignition wires: A popping noise during startup can be caused by faulty spark plugs or ignition wires. These components are responsible for delivering the electrical spark that ignites the air/fuel mixture in the engine. If they are damaged or worn out, the spark may not be properly transmitted, which can result in a popping or knocking noise.
2. Bad engine mounts: The engine mounts are rubber cushions that hold the engine in place and absorb vibrations. Over time, these mounts can wear out and crack, allowing the engine to move excessively. This can also cause a popping noise during startup.
3. Damaged starter: The starter is responsible for engaging the engine's flywheel and starting the engine. If the starter is damaged or faulty, it may not be able to engage the flywheel properly, resulting in a popping noise.
4. Transmission problems: A popping noise when starting the Expedition could also be due to a problem with the transmission. This could be caused by low transmission fluid, worn-out gears, or a faulty torque converter.
