INTAKE AIR SYSTEM

This above is a simplified diagram of the intake air system. The intake air system consists of (following the air path) the air filter box, the Air Flow Meter (AFM), the air funnel, the throttle body (which houses the throttle plates), the dynamic air chamber, and the intake manifold. Bypass air to control idle is not discussed here (see the bypass air section).

AIR FLOW METER (AFM)

The Air Flow Meter (AFM) is of the "flapper" type. When no air enters the engine, the measuring plate is closed. As air enters the engine, the measuring plate opens. By connecting the measuring plate to a potentiometer (variable resistance), the Engine Control Unit (ECU) is able to determine the volume of air entering the engine at any time. An air intake temperature sensor is integrated into the AFM. This enables the ECU to determine the air mass from the air volume. The AFM has also a built-in switch to turn off fuel pump operation when the measuring plate is closed (engine not running). This is a safety measure (see fuel system).

THROTTLE PLATES

This above shows the throttle plates (primary and number 2 secondary plates) after having removed the air funnel. The primary plate is at the bottom. The secondary plates are at the top. There are two sets (of two) secondary plates. The number 1 secondary plates are on the same plane as the primary plate. They are behind the number 2 secondary plates in the drawing above. The number 1 secondary plates are tied mechanically to the primary plate. They open when the primary plates have reached a certain angle.

The number 2 secondary plates are open unless enough vacuum (200mm Hg or 7.87in Hg) is applied to the double throttle diaphragm, in which case, they are closed. Vacuum to the diaphragm comes from the intake manifold via a heat activated water thermo valve. Opening of the number 2 secondary plates is dampened by the double throttle diaphragm, in other words, if vacuum becomes low enough to make the plates open, they will open slowly.

This above is the Factory Service Manual (FSM) test to check for proper operation of the water thermo valve. Port A is connected to the double throttle diaphragm. Port B connects to a vacuum source in the intake manifold. Port C is open to atmospheric pressure. When the water temperature is below 60 degrees Celsius (engine cold), vacuum passes from intake manifold to the double throttle diaphragm. When the temperature is above 60 degrees Celsius, the diaphragm sees no vacuum because the valve vents to the atmosphere, meaning that the plates are open. There is a delay valve in the vacuum line connecting the water thermo valve to the double throttle diaphragm. The purpose of this delay valve is to slow down (by a few seconds) the vacuum drop at the double throttle diaphragm. To sum it all up, when engine is cold, the number 2 secondary plates are closed when vacuum is high (e.g., at idle). When the accelerator pedal is pushed down, the intake manifold vacuum drops causing the number 2 secondary plates to open with a delay (thanks to the delay valve). When engine is hot, the number 2 secondary plates are always open.

AUXILIARY PORTS

The auxiliary port valve system allows a better flow of intake air by opening an auxiliary port in addition to the primary and secondary ports. The opening of the auxiliary port is controlled by the auxiliary port valve. At low engine speeds, the auxiliary port is closed. When the engine speed is high enough and under certain conditions, the valve starts opening the auxiliary port.

This above describes the operation of the auxiliary port valve system. The pressure line going from the air pump to the actuator exists only on the mazda rx-7 89-91. On the 86-88, the pressure line to the actuator is teed into the split air pipe (see emissions section under secondary air injection). When the auxiliary port valve rotates, the auxiliary port opens. The more the valve rotates, the bigger the actual port opening becomes. The rotation of the valve is controlled by an actuator which is itself pressure controlled.

This above shows the split air pipe and the pressure line to the actuators on the mazda rx-7 86-88. The actuators see a pressure equal to the sum of the pressure in the split air pipe (coming from air pump operation) and the pressure in the exhaust pipe itself (at the level of the main converter). It appears that air is injected into the split air pipe only under medium load (below 3,500 rpm). This means that under any other condition, the pressure needed to activate the actuators comes from exhaust pressure only.

This above is the Factory Service Manual (FSM) test to check for proper operation of the actuators. The actuator begins to turn the auxiliary port valve when the exhaust pressure reaches 1.2 psi. The valve is fully turned when the pressure reaches 2.1 psi.