See Figure 1
The Bottom Feed Port (BFP) injection system is used on the 1995-97 2.2L OHV (VIN 4) engines.
The function of the fuel metering system is to deliver the correct amount of fuel to the engine under all operating conditions. In this system, fuel is delivered to the engine by individual bottom feed type multi-port fuel injectors mounted in the lower intake manifold near each cylinder.
The Powertrain Control Module (PCM) pulses the fuel injectors in pairs. Alternate pairs are pulsed every 180° of crankshaft revolution. This is called Alternating Synchronous Double Fire (ASDF) injection. The PCM uses two injector driver circuits, each controlling a pair of injectors. The current in each circuit is allowed to climb to a peak of 4 amps and then is reduced to 1 amp to hold the injector open. This happens very quickly.
The main control sensor of this system is the Oxygen (O 2 ) sensor, located in the exhaust manifold. This sensor indicates to the computer control module how much oxygen is in the exhaust gas, and the PCM changes the air/fuel ratio to the engine by controlling the fuel injectors. The best mixture to keep exhaust emissions to a minimum is 14.7:1 which allows the catalytic converter to operate most efficiently. Because of the constant measuring and adjusting of the air/fuel ratio, the fuel injection system is called a Closed Loop system.