Abstract: An air fuel ratio management system having a calibration correction for the pressure differentials between the exhaust and intake manifolds of the engine is disclosed. The differential calibration corrects the air/fuel ratio of the system for the variable internal exhaust gas recirculation occasioned by changing restrictions to flow found in the intake and exhaust manifolds. In one implementation a differential pressure sensor communicates with both the intake and exhaust manifolds to develop a differential pressure signal. The differential pressure signal is thereafter applied to a function circuit which generates a pressure correction signal. An electronic control unit receives the pressure correction signal and utilizes it to modify the air/fuel ratio calibration according to the functional conversion. In the preferred embodiment the function circuit comprises a voltage controlled linear current source.

Abstract: Disclosed herein is a start enrichment circuit for an electronic fuel control system when the engine temperature is above or below its nominal operating temperature range. The circuit produces a start enrichment signal having an initial temperature dependent value while the starter is being energized which decay as a function of time after the engine starts. The preferred embodiment also provides a start enrichment signal within the nominal engine temperature range when the exhaut gas recirculation valve is in an activated state.