Injection Timing: Description and Operation

The ECM contains the memory for basic discharge duration at various engine speeds and manifold pressures. The basic discharge duration, after being readout from the memory, is further modified by signals sent from various sensors to obtain the final discharge duration.
By monitoring Long Term Fuel Trim, the ECM detects long term malfunctions in the fuel system, and will set a Diagnostic Trouble Code (DTC) if the malfunction occurs during two consecutive trips.