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h21 overview of AIS air intake sys.pdf

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H21 OVERVIEW OF AIS AIR INTAKE SYS
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Overview Of The Air Induction System The purpose of the air induction system is to filter, meter, and measure intake air flow into the engine. Air, filtered by the air cleaner, passes into the intake manifold in varying volumes. The amount of air entering the engine is a function of throttle valve opening angle and engine rpm. Air velocity is increased as it passes through the long, narrow intake manifold runners, resulting in improved engine volumetric efficiency. Intake air volume is measured by movement of the air flow meter measuring plate or by detecting vortex frequency on engines equipped with L type EFI. On engines equipped with D type EFI, air volume is measured by monitoring the pressure in the intake manifold, a value which varies proportionally with the volume of air entering the engine. The throttle valve directly controls the volume of air which enters the engine based on driver demand. Additionally, when the engine is cold, it is necessary for supplementary air to by-pass the closed throttle valve to provide cold fast idle. This is accomplished by a bi- metallic or wax type air valve or by an ECU controlled Idle Speed Control Valve (ISCV). EFI #2 - AIR INDUCTION SYSTEMPage 1 ? Toyota Motor Sales, U.S.A., Inc. All Rights Reserved. Air Induction System Components Vane Air Flow Meter (L Type EFI) The vane type air flow meter is a commonly used air volume measurement device on Toyota EFI engines. The meter consists of a measuring plate, which is spring loaded closed by a return spring, and a potentiometer attached to the plate, which varies an electrical signal to the ECU as the position of the plate changes. Air volume entering the engine is directly proportional to the amount of movement detected from the measuring plate. Additionally, the air flow meter incorporates a fuel pump enable contact which breaks the ground circuit of the circuit opening relay if the engine stops running. The air flow meter is placed in series between the air cleaner and the throttle body, thereby measuring all air which enters the engine. Integrated with the air flow meter is an intake air temperature sensor and an idle mixture by-pass passage. Idle Mixture Air By-pass Circuit For proper calibration of the engine air/fuel ratio at idle speed, an idle mixture air by-pass circuit is incorporated into the air flow meter. A screw is used to adjust the amount of air which by-passes the measuring plate. This screw is adjusted and sealed at the factory to discourage improper adjustment and tampering. There are no provisions or specifications for field adjustment. After factory calibration of the air flow meter, a two-digit number is stamped into the meter casting near the idle mixture adjusting screw. This number indicates the distance from the casting to the flat surface of the screw and can be used as a reference if the idle mixture screw has been tampered with. The calibration number can be interpreted by referring to the examples in the following chart. EFI #2 - AIR INDUCTION SYSTEMPage 2 ? Toyota Motor Sales, U.S.A., Inc. All Rights Reserved. Fuel Pump Circuit Control A fuel pump switch is incorporated into the air flow meter to prevent the fuel pump from running unless the engine is running. Any movement of the air flow meter measuring plate will cause the fuel pump switch contact to close. When the engine is not running, the measuring plate forces the fuel pump switch contact open, preventing the circuit opening relay from operating. For more information on the fuel pump electrical circuit, refer to section 3, “Fuel Delivery and Injection Control.“ Karman Vortex Air Flow Meter (L Type EFI) The Karman vortex air flow meter is used only on limited applications (7M-GTE and Lexus 1UZ-FE rod extends ? ECU turns VSV OFF on deceleration; rod allows throttle to close slowly ? Engine OFF; rod extends, holding throttle open slightly EFI #2 - AIR INDUCTION SYSTEMPage 5 ? Toyota Motor Sales, U.S.A., Inc. All Rights Reserved. Air Valves There are two types of non-ECU controlled air valves used on some engines to control cold engine fast idle. These valves, the electrically heated bi-metal type and the coolant heated wax type, vary the amount of air bypassing the closed throttle valve during cold engine operation. Bi-metal Type Air Valve This gate valve operates on the principle of a spring loaded gate balanced against a bi- metal element. The tension of the bi-metallic element varies the position of the gate as its temperature changes. The bi-metal element is heated by an electrical heater coil and by the temperature of the ambient air surrounding it. The air valve assembly is installed on the surface of the cylinder head to keep the gate valve closed during hot soak periods. EFI #2 - AIR INDUCTION SYSTEMPage 6 ? Toyota Motor Sales, U.S.A., Inc. All Rights Reserved. Heater current for the air valve is supplied by the circuit opening relay power contact, the same circuit which feeds the fuel pump. Air valve operation can be quick checked by pinching off a supply hose and observing the rpm drop. When checked with a warm engine, the drop should be less than 50 rpm. When the engine is cold, the rpm drop should be high. EFI #2 - AIR INDUCTION SYSTEMPage 7 ? Toyota Motor Sales, U.S.A., Inc. All Rights Reserved. Wax Type Air Valve The wax type air valve is integrated with the throttle body and varies an idle air by-pass opening as coolant temperature changes. The valve works on the principle of a spring loaded gate valve balanced against a coolant heated, wax filled thermo valve. When coolant temperature is cold, the wax filled thermo valve retracts allowing spring A to push the gate valve open. This allows air to flow from the air cleaner side of the valve to the intake side of the valve. As coolant temperature rises, the wax filled thermo valve expands allowing spring B to gradually close the valve (spring B is stronger than spring A). This causes engine rpm to decrease as air flow to the intake is decreased. The wax type air valve should be fully closed by the time engine coolant temperature reaches approximately 80'C (176'F). ? Cold engine, large rpm drop ? Fully warmed engine!~100 rpm drop EFI #2 - AIR INDUCTION SYSTEMPage 8 ? Toyota Motor Sales, U.S.A., Inc. All Rights Reserved. A good quick check for the wax type air valve is to observe engine rpm throughout the warm up cycle. Look for high rpm upon initial startup and gradual reduction to normal curb idle speed as the engine reaches normal operating temperature. On D type EFI, the valve operation can also be checked by removing the air inlet pipe at the throttle body and blocking the fresh air port inside the throttle bore. When the engine is cold, engine rpm should drop greater than 100 rpm. Once the engine reaches normal operating temperature (~~ 176'F), rpm drop should not exceed 100 rpm. Intake Air Chamber manifold pressure is applied to the other side of the chip. As the chip flexes, the mechanical movement is converted into a variable voltage signal by the sensor. There are several different names used in reference to the Manifold Absolute Pressure sensor, depending on the publication you read. Two other common names used to refer to this sensor are PIM, or Pressure Intake Manifold, and Vacuum sensor. For more information about operation of the manifold absolute pressure sensor and its signal characteristics, refer to “Electronic Engine Controls.“ EFI #2 - AIR INDUCTION SYSTEMPage 10 ? Toyota Motor Sales, U.S.A., Inc. All Rights Reserved.
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