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h22 fuel delivery inject control.pdf

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H22 FUEL DELIVERY INJECT CONTROL
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Overview of the Fuel Delivery System The fuel delivery system incorporates the following components: 1) Fuel tank (with evaporative emissions controls) 2) Fuel pump 3) Fuel pipe and in line filter 4) Fuel delivery pipe (fuel rail) 5) Pulsation damper (many engines) 6) Fuel injectors 7) Cold start injector (most engines) 8) Fuel pressure regulator 9) Fuel return pipe Fuel is pumped from the tank by an electric fuel pump, which is controlled by the circuit opening relay. Fuel flows through the fuel filter to the fuel rail (fuel delivery pipe) and up to the pressure regulator where it is held under pressure. The pressure regulator maintains fuel pressure in the rail at a specified value above intake manifold pressure. This maintains a constant pressure drop across the fuel injectors regardless of engine load. Fuel in excess of that consumed by engine operation is returned to the tank by way of the fuel return line. A pulsation damper, mounted to the fuel rail, is used on some engines to absorb pressure variations in the fuel rail due to injectors opening and closing. The fuel injectors, which directly control fuel metering to the intake manifold, are pulsed by the ECU. The ECU completes the injector ground circuit for a calculated amount of time referred to as injection duration or injection pulse width. The ECU determines which air/fuel ratio the engine runs at based upon engine conditions monitored by input sensors and a program stored in its memory. During cold engine starting, many engines incorporate a cold start injector designed to improve startability below a specified coolant temperature. EFI #3 - FUEL DELIVERY consult the repair manual for actual specifications and procedures. CAUTION: Perform this test only long enough to determine if pressure rises above minimum specification; risk exists of blowing coupler hose off of pump. This test is only necessary if other pressure tests indicate lower than normal fuel pressure. Fuel Injectors The fuel injector is an electro-mechanical device which meters, atomizes and directs fuel into the intake manifold based on signals from the ECU driver circuit(s). All Toyota engines used in the U.S.A. position the injectors, one per cylinder, directly behind the intake valve. The injectors are installed with an insulator/seal on the manifold end to isolate the injector from heat and to prevent an atmospheric pressure leak into the manifold. The fuel delivery pipe serves to secure the injector in place. Fuel is sealed on the delivery pipe end by an O-ring and grommet. To reduce the possibility of vapor lock, which tends to occur during high temperature operation, the 3S-GTE and 2TZ-FE engines use a side feed injector. This type of injector seals with an upper and lower O-ring. O- rings and insulators should always be replaced when injectors are removed; they should never be re-used. EFI #3 - FUEL DELIVERY & INJECTION CONTROLPage 10 ? Toyota Motor Sales, U.S.A., Inc. All Rights Reserved. Air Assist System To promote better fuel atomization, the 3VZ- FE engine uses an air assist system which meters air from the Idle Speed Control (ISC) valve directly to the nozzle of the fuel injector. An adaptor for the air assist system is added to a standard two-hole type injector to provide an air distribution gallery. Air is mixed with fuel in the chamber formed by the injector insulator grommet and the lower O-ring. EFI #3 - FUEL DELIVERY & INJECTION CONTROLPage 11 ? Toyota Motor Sales, U.S.A., Inc. All Rights Reserved. Types Of Injectors In Use Toyota currently uses four different types of fuel injectors depending on engine application. These can be broken down into pintle type and hole type (cone valve and ball valve), high resistance and low resistance. Pintle Type Injector - This was the original design used on early Conventional and EFI/ TCCS engines. This injector gets its name from the type of valve used to control fuel atomization and flow. It offers good atomization of fuel but is susceptible to deposit buildup on the pintle valve. Deposits cause restriction to fuel flow promoting lean fuel delivery and altered injector spray pattern. Hole Type Injector - Hole type injectors were introduced on later model EFI/TCCS engines to reduce concerns with injector deposits. The inject.on valve is recessed from the tip of the injector and fuel is delivered through holes drilled in a director plate at the injector tip. The hole type injector offers good fuel atomization while demonstrating better resistance to deposit buildup compared to the pintle design. There are currently three designs of hole type injectors in use, including a side feed injector used on the 3S- GTE and 2TZ-FE engines. High And Low Resistance Injector Windings There are two different types of injector coil windings used depending on the type of drive circuit used and whether or not an external resistor is being used. Low resistance injectors, which typically range between 2 - 3 W @ 70'F, are used with an external resistor in a voltage controlled driver circuit. Low resistance injectors are also used without an external resistor in a current controlled driver circuit. High resistance injectors, which typically run about 13.8 W @ 70'F, do not require the use of an external resistor in a voltage controlled driver circuit. EFI #3 - FUEL DELIVERY & INJECTION CONTROLPage 12 ? Toyota Motor Sales, U.S.A., Inc. All Rights Reserved.
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