Synchronous Injection
WARNING: This page is about a different car, the 2004 Pontiac Vibe. However, it is still accessible from the selected car via links, so may be relevant.
When starting the engine, the fuel injectors inject the fuel simultaneously and synchronously at every camshaft position (CMP) sensor signal. When the engine is starting at a cold state, the amount of fuel is determined by the engine coolant temperature (ECT) sensor and is divided and injected.
Once the engine is running, the fuel injection occurs in a cylinder only when the cylinder is in the exhaust stroke. The PCM detects the compression stroke of cylinder 1 through the CMP sensor signal.