How Digital Engine Management Systems Control Ignition and Fuel Injection

Digital Engine Management System: Ignition and Injection

The integrated digital ignition system and the UEC injection system use digital 1s and 0s, and a filter circuit converts interference signals from the analog sensors into digital signals that the microprocessor can process. The conversion takes place in two stages:

• Quantification: represents the magnitude of the signal as a finite number of values.
• Encoding: represents each quantified value as a binary code.

Fuel Pump Control

The electric fuel pump is powered by a relay with a pump contact. When the ignition is switched on, the UEC receives a positive signal for one second. If the UEC does not receive engine speed (rpm) signals from the crankshaft sensor, it cuts the pump circuit and does not energize the pump again.

Injection and Air Metering

The UEC receives signals from the coolant temperature sensor, the air flow meter, and the throttle position sensor. The injection time is calculated from these inputs and can be modified through the basic settings stored in memory. If the air filter or air intake is restricted, the signal from the air flow meter changes and the UEC adjusts the injection accordingly.

Cold Start and Idle Control

During cold start, the UEC activates the cold-start injector and extra fuel enhancement for a set duration, depending on engine temperature. The idle speed is regulated by an idle air control valve, which bypasses air around the closed throttle. When the engine is cold, this increases idle air to speed up warm-up and stabilize the engine.

Throttle Position and Idle Stabilization

The throttle position sensor, a potentiometer mounted on the throttle shaft, sends a voltage proportional to the throttle angle to the UEC. The UEC uses this information, together with engine speed, to stabilize idle and to detect acceleration, deceleration, and full-load operation.

Knock Control and Ignition Timing

The knock sensor detects vibrations in the engine block in the frequency range of 8 to 12 kHz. The UEC filters out unrelated vibrations and evaluates whether the knock level exceeds a set threshold. If knock is detected, the UEC retards ignition timing by approximately 0.5 degrees per event, and advances it gradually when knock is no longer detected. This protects the engine while maximizing power and efficiency.

Service Signals

The UEC uses signals from the sensors to adjust idle air, ignition timing, and injection. When the engine is started, the UEC emits an ignition pulse through the output amplifier to the primary coil, which provides accurate idle regulation. The UEC also reads additional signals from the vehicle, and when the UEC box is connected, it receives automatic rpm signals for diagnostics and monitoring.