To further improve fuel distribution, the fuel injection cycle on MPI configurations can be timed to occur as the engine’s intake valve opens, which further reduces the wet flow effect in the intake ports and cylinders.
As the federal government mandated stricter exhaust emissions and fuel economy standards, MPI became the fuel system of choice for all domestic and import manufacturers. To reduce wet flow and thus improve cylinder-to-cylinder fuel distribution, domestic auto manufacturers introduced multi-port injection (MPI) on a limited number of higher-end vehicles.
The resulting “wet flow” or stream of liquid fuel following the intake passages created an uneven distribution of fuel among the engine’s cylinders. Fuel was delivered to the engine by an in-tank fuel pump and regulated by a fuel pressure regulator built into the TBI assembly.Īlthough TBI was extremely simple, fuel droplets separated from the air stream as the intake charge followed the curved outer circumferences of intake passages. A throttle position sensor (TPS), coolant temperature sensor (CTS), manifold absolute pressure (MAP) and oxygen (O2) sensor, were the primary sensors needed to establish accurate fuel control on the engine.
TBI required a simple computer capable of operating one or two fuel injectors that sprayed directly into the air stream entering the intake manifold. The basic idea behind TBI is to make a fuel injection system that could easily replace the carburetor on existing engine designs. Most parts professionals recall that throttle body injection (TBI) was one of the first domestic fuel injection systems to enter the market.
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