Renix Throttle Body Fuel Injection (TBFI), Early Type System

Fig. 1 Renix throttle body fuel injection system, early type:

This throttle body fuel injection system, Fig. 1, is a pulse time system that injects fuel into the throttle body above the throttle blade. Fuel is metered to the engine by an electronically controlled fuel injector.

Injection is controlled by an electronic control unit according to sensors that detect coolant temperature, crankshaft position, exhaust gas oxygen content, manifold absolute pressure and throttle position.

When the system is activated by the ignition switch, the fuel pump is activated by the electronic control unit and operates for approximately one second unless the engine is running or the starter is engaged. All engine sensors are then activated and begin providing inputs to the control unit. The EGR solenoid is activated to block vacuum to the EGR valve when coolant temperature is below 110°F.

When the engine is started, the fuel pump is activated for continuous operation. The idle speed control motor will control idle speed if the throttle position sensor is closed. The ignition advance shifts from base ignition timing to the control unit programmed advance curve. The fuel pressure regulator maintains fuel pressure at approximately 14.5 psi by returning excess fuel to the tank.

The electronic control unit continuously receives and uses sensor outputs for barometric pressure, engine coolant temperature, engine speed, intake manifold absolute pressure, intake manifold air temperature and throttle position.

The ECU provides a ground for the injector and precisely controls the opening and closing time to deliver fuel to the engine.