What is the engine starting process?

[Rylee]

When the key is turned to the ON position, the ECU powers on. Once the ECU is powered, it supplies electricity to the corresponding sensors through various pins and retrieves sensor information to control the engine's operation. At the same time, the fuel pump in the tank powers on and operates for 3-5 seconds to provide sufficient pressure to the fuel supply system. Many people often say to wait for the self-check before starting, but this is actually unnecessary. However, some cars may have issues with the fuel pump pressure relief valve or fuel injector leakage, which can cause a drop in fuel system pressure after prolonged parking. If started directly, the fuel pump may not have enough time to build sufficient pressure, leading to an extended starting time. When the key is turned to the START position, the solenoid coil on the starter is energized and engages. Through lever action, the starter drive gear is pushed outward to mesh with the flywheel ring gear. While the drive gear is pushed out, the other end of the lever closes the circuit contact of the starter motor, allowing the starter motor to power on and begin rotating, driving the flywheel. The starter drives the flywheel to rotate, which in turn drives the crankshaft. The crankshaft moves the pistons back and forth via connecting rods, while also driving the timing gear through a timing belt or chain to control the intake and exhaust valves inside the cylinder head via the camshaft. Simultaneously, the crankshaft position sensor continuously sends crankshaft angle data to the ECU, which determines which cylinder should receive fuel injection and ignition. For a specific cylinder, when the piston moves downward, the camshaft opens the intake valve and closes the exhaust valve. The ECU, based on the crankshaft position sensor signal, decides to supply fuel, so the fuel injector solenoid opens, spraying atomized gasoline toward the back of the intake valve at the end of the intake manifold under fuel system pressure. The strong intake airflow carries the gasoline into the cylinder. When the piston reaches bottom dead center, it begins the compression stroke. At this point, both intake and exhaust valves are closed, and the piston compresses the air-fuel mixture in the cylinder. The airflow inside the cylinder continues to move, further atomizing and evaporating the gasoline. When the piston nears top dead center, the ECU detects the ignition timing via the crankshaft position sensor signal, energizing the ignition coil to produce a spark plug arc, igniting the mixture for combustion. During cold starts, due to low temperatures and poor gasoline evaporation, the ECU increases fuel injection to ensure enough gasoline evaporates for a sufficiently concentrated mixture, guaranteeing a successful start. This results in some unburned gasoline, leading to a noticeable gasoline smell from the exhaust during cold starts—a normal phenomenon that disappears as fuel injection decreases after startup. Once each cylinder can achieve stable ignition, the engine generates enough torque to sustain its own operation. At this point, releasing the key returns the ignition switch to the ON position, cutting power to the starter. If the key is released too late, the flywheel may back-drive the starter, producing an unpleasant noise. After a successful cold start, the engine speed will be much higher than idle due to the fast warm-up function. At this stage, the engine is fully started.

[Madeleine]

I haven't been learning to drive for long, and I still find it magical every time I start the engine. Get in the car, insert the key or press the start button, first turn to the ACC position to light up the dashboard, then turn all the way to the start position. At this point, the battery releases current to the starter motor, and the small gear engages with the large ring gear of the flywheel, causing it to rotate. The flywheel drives the crankshaft to rotate, and the pistons in the cylinders move up and down, drawing in a mixture of air and fuel. Then, the spark plug emits an electric spark to ignite the gas, and the combustion generates force to push the piston, causing the engine to hum and start running. Cold starts in winter might be a bit slower because the oil is too viscous or the battery is weak, so you might need to press the accelerator a bit more or warm it up for a few seconds. I remember my instructor said not to start the engine more than three times in a row to avoid damaging the battery. During maintenance, checking if the terminals are corroded can help with smoother starts. Nowadays, new cars with push-button start work on a similar principle but are much quieter. Before hitting the road, I always like to warm it up for a while to let it run smoothly.