Engine Systems Control Unit (Mas)

The MAS functions as fuel pump relay, A/C compressor control, O2 sensor heating control, air injection control, malfunction memory and diagnostics input for CIS-E control unit, and maximum engine RPM limiter (6450 RPM). The MAS monitors and signals CIS-E control unit for the following:

• A/C compressor engagement. CIS-E control unit responds by increasing engine idle speed.
• O2 sensor heater is at operating temperature. Based on voltage signals from O2 sensor, CIS-E control unit controls fuel mixture to maintain a 14.7:1 air/fuel ratio. If O2 sensor fails, CHECK ENGINE light will illuminate to indicate malfunction code is stored in CIS-E control unit and MAS.
• Air injection system is operating or not operating so CIS-E control unit will monitor input from O2 sensor correctly.
• Malfunction memory for and diagnostics input to CIS-E control unit as alternate test unit to compare diagnostic data and as a buffer unit to protect CIS-E control unit circuitry.
• Maximum engine RPM limiter senses engine speed based on impulses from diagnostic terminal of ignition switching unit (EZL). CIS-E control unit uses information to govern engine speed by changing electrical current to Electrohydraulic Actuator (EHA), which in turn controls fuel pressure regulator. When engine reaches maximum RPM (6450), CIS-E control unit signals EHA to increase vacuum pressure at fuel pressure regulator, causing an interruption in fuel supply to injection valves and resulting in a leaner fuel mixture. Maximum engine RPM signal also causes fuel pump relay to interrupt contact between circuits No. 30 and 87 and shut off fuel pump.