Fuel Injection Control

The ECU calculates base injection pulse width by processing signals from the crank angle sensor and airflow meter. After receiving signals from each sensor that detects various engine conditions, the ECU adds enrichments, which are preprogrammed into the control unit, to the base injection width. This makes the optimum mixture available throughout a wide variety of conditions. Fuel enrichment is always available under the following conditions: during warm-up, starting, after idle, under heavy load and when cylinder head temperature is high.

This fuel injection system incorporates mixture ratio feedback. It is designed to maintain the mixture ratio a precise point. Through the use of an exhaust gas sensor located in the exhaust manifold, the ECU can determine whether to richen or lean out the air/fuel ratio to precisely control exhaust emissions. This takes place during closed loop operation and continuously monitors itself to stay within an acceptable emissions output range. However, this system is overridden and will operate under open loop when one or more of the following conditions exist: starting, engine and exhaust sensor are cold, driving at high speeds or under heavy load, at idle, exhaust gas sensor monitors a too lean condition for over 10 seconds, fuel shut-off in operation, exhaust gas sensor is malfunctioning or pressure regulator control system is in operation.

Two methods of fuel injection are used. They are simultaneous and group injection. In simultaneous injection, fuel is injected into all 6 cylinders at the same time. In group injection, the 6 injectors are divided into 2 groups and fuel is injected into each group of injectors separately. When any of the following conditions are met, fuel injection shifts from group to simultaneous: engine speed more than 300 RPM, cylinder head temperature is below 140°F (60°C) and during starting.