On vehicles with a 3.1 liter engine (V6) injection unit (TBI) replaces the conventional carburetor above the intake manifold. Cars with a 3.8 liter engine are equipped with a multipoint injection system (PFI). TBI systems are controlled by the ECM, while PFI systems are controlled by the PCM. The ECM/PCM systems monitor engine operation and regulate the proper fuel/air mixture delivery (a complete description of the ECM/PCM control systems is contained in chapter 6).
An electric fuel pump, located in the fuel tank with a fuel gauge, forces fuel into the system through the fuel supply line and fuel filter.
Note. The 3.1L engine has a dual turbine pump (provides medium pressure), while the 3.8L engine is equipped with a vane pump (provides high pressure). In addition, the 3.8L engine is equipped with a pulsator (see illustration 7.8) to equalize pressure fluctuations during pump operation.
The pressure regulator maintains a constant fuel pressure. Part of the fuel is returned through a separate line to the fuel tank.
The TBI basic block consists of two main cast blocks: a throttle body with an idle air booster spool (IAC), airflow control, and throttle position sensor (TPS), monitoring the angle of rotation of the damper. The injector body consists of a fuel supply meter with a built-in pressure regulator and a fuel injector for supplying fuel to the engine.
The injector is a solenoid based device controlled by the ECM. The ECM activates a solenoid that lifts the valve off the seat. Pressurized fuel is injected above the throttle valve. Fuel not used by the injector passes through the pressure regulator before returning to the fuel tank.
On systems with distributed injection (PFI) The throttle body has a valve to control the amount of air entering the engine. The throttle position sensor is located on the throttle body (TPS) and IAC valves.
The distributor tube is located on top of the engine. It distributes fuel to individual injectors.
Fuel is supplied to the tube through the fuel supply line and through the distribution tube enters the pressure regulator. The regulator keeps the pressure at the injectors constant.
The rest of the fuel is returned to the gas tank.