Tandem Control System (Civic Standard)
The tandem valve is employed on throttle body injected Civic models to improve fuel atomization. This is accomplished by regulating venturi vacuum (to tandem valve actuating diaphragm) through an ECU controlled solenoid valve. When valve is deactivated, vacuum is not applied to diaphragm and valve is nearly closed. The reduced side clearance caused by closed valve creates an increase in intake air velocity. See Fig 1 . This promotes a more complete atomization of fuel from main fuel injector, regardless of airflow rate. Venturi vacuum is allowed to activate diaphragm when coolant temperature is greater than 160°F (70°C) or engine speed is greater than 1500 RPM (auto. trans.) or 2000-2800 RPM (man. trans.), depending upon atmospheric pressure.