Fuel Injection Control

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

This fuel injection system incorporates mixture ratio feedback. It is designed to maintain a precise mixture ratio. Through the use of an exhaust gas sensor located in the exhaust manifold, the ECU can determine whether to enriched or lean out the air/fuel ratio to precisely control exhaust emissions and engine performance. This function takes place during closed loop operation and continuously monitors itself to stay within an acceptable emissions output range. However, this feedback system can be overridden and will operate in open loop when one or more of the following conditions exist: starting, engine and/or exhaust sensor 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 solenoid activated, exhaust gas sensor malfunctioning or pressure regulator control system in operation.

Two methods of multi-port fuel injection are used. They are simultaneous and group injection. In simultaneous injection, fuel is injected into all 4 or 6 cylinders at the same time. In group injection, the 4 or 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 exceeds 300 RPM, cylinder head temperature is below 140°F (60°C) and during starting.