System diagnosis
Another important feature of microcomputer engine control systems is their ability to diagnose failures in their control systems and alert the operator. Sensor and actuator failures or mis-adjustments can be…
Automatic system adjustment
Another important feature of microcomputer engine control systems is their ability to be programmed to adapt to parameter changes. Many control systems use this feature to enable the computer to…
Evaporative emissions canister purge
During engine-off conditions, the fuel stored in the fuel system tends to evaporate into the atmosphere. To reduce these HC emissions, the fuel tank is sealed and evaporative gases are…
Closed-loop ignition timing
The ignition system described in the foregoing section is an open-loop system. The major disadvantage of open loop control is that it cannot automatically compensate for mechanical changes in the…
Electronic ignition control
An engine must be provided with fuel and air in correct proportions and the means to ignite this mixture in the form of an electric spark. Before the development of…
EGR control
A second electronic engine control subsystem is the control of exhaust gas that is recirculated back to the intake manifold. Under normal operating conditions, engine cylinder temperatures can reach more…
Idle air control
A block diagram of a simplified idle speed control system is shown in Fig. b. Idle speed is detected by the RPM sensor, and the speed is adjusted to maintain…
Idle speed control
Idle speed control is used by some manufacturers to prevent engine stall during idle. The goal is to allow the engine to idle at as low an RPM as possible,…
Deceleration leaning
During periods of light engine load and high RPM such as during coasting or hard deceleration, the engine operates with a very lean air/fuel ratio to reduce excess emissions of…
Closed-loop control
Perhaps the most important adjustment to the fuel injector pulse duration comes when the control is in the closed-loop mode. In the open-loop mode the accuracy of the fuel delivery…
