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In this tutorial, I would like to put forth few importants points on Electronic Fuel Injection system, with particular focus upon the sensors and actuators, and their inputs and outputs to and from the vehicle's ECM.
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Overview
Both the multi-point and the single-point systems operate in a very similar fashion, having an electromechanically operated injector or injectors opening for a predetermined length of time called the injector pulse width. The pulse width is determined by the engine’s Electronic Control Module (ECM and depends on the engine temperature, the engine load and the information from the oxygen (lambda) sensor. The fuel is delivered from the tank through a filter, and a regulator determines its operating pressure. The fuel is delivered to the engine in precise quantities and in most cases is injected into the inlet manifold to await the valve’s opening, then drawn into the combustion chamber by the incoming air.
The Fuel Tank
This is the obvious place to start in any full system explanation. Unlike the tanks on early carburettor-equipped vehicles, it is a sealed unit that allows the natural gassing of the fuel to aid delivery to the pump by slightly pressurising the system. When the filler cap is removed, pressure is heard to escape because the fuel filler caps are no longer vented.
The Fuel Pump
This type of high-pressure fuel pump (Fig 1.0) is called a roller cell pump, with the fuel entering the pump and being compressed by rotating cells which force it through the pump at a high pressure. The pump can produce a pressure of 8 bar (120 psi) with a delivery rate of approximately 4 to 5 litres per minute. Within the pump is a pressure relief valve that lifts off its seat at 8 bar to arrest the pressure if a blockage in the filter or fuel lines or elsewhere causes it to become obstructed. The other end of the pump (output) is home to a non-return valve which, when the voltage to the pump is removed, closes the return to the tank and maintains pressure within the system. The normal operating pressure within this system is approximately 2 bar (30 psi), at which the current draw on the pump is 3 to 5 amps. Fuel passing across the fuel pump's armature is subjected to sparks and arcing; this sounds quite dangerous, but the absence of oxygen means that there will not be an explosion!
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The majority of fuel pumps fitted to today’s motor vehicles are fitted within the vehicle’s petrol tank and are referred to as ‘submerged’ fuel pumps. The pump is invariably be located with the fuel sender unit and both units can sometimes be accessed through an inspection hole either in the boot floor or under the rear seat. Mounted vertically, the pump comprises an inner and outer gear assembly that is called the ‘gerotor’. The combined assembly is secured in the tank using screws and sealed with a rubber gasket, or a bayonet-type locking ring. On some models, there are two fuel pumps, the submerged pump acting as a ‘lift’ pump to the external roller cell pump.
Both the multi-point and the single-point systems operate in a very similar fashion, having an electromechanically operated injector or injectors opening for a predetermined length of time called the injector pulse width. The pulse width is determined by the engine’s Electronic Control Module (ECM and depends on the engine temperature, the engine load and the information from the oxygen (lambda) sensor. The fuel is delivered from the tank through a filter, and a regulator determines its operating pressure. The fuel is delivered to the engine in precise quantities and in most cases is injected into the inlet manifold to await the valve’s opening, then drawn into the combustion chamber by the incoming air.
The Fuel Tank
This is the obvious place to start in any full system explanation. Unlike the tanks on early carburettor-equipped vehicles, it is a sealed unit that allows the natural gassing of the fuel to aid delivery to the pump by slightly pressurising the system. When the filler cap is removed, pressure is heard to escape because the fuel filler caps are no longer vented.
The Fuel Pump
This type of high-pressure fuel pump (Fig 1.0) is called a roller cell pump, with the fuel entering the pump and being compressed by rotating cells which force it through the pump at a high pressure. The pump can produce a pressure of 8 bar (120 psi) with a delivery rate of approximately 4 to 5 litres per minute. Within the pump is a pressure relief valve that lifts off its seat at 8 bar to arrest the pressure if a blockage in the filter or fuel lines or elsewhere causes it to become obstructed. The other end of the pump (output) is home to a non-return valve which, when the voltage to the pump is removed, closes the return to the tank and maintains pressure within the system. The normal operating pressure within this system is approximately 2 bar (30 psi), at which the current draw on the pump is 3 to 5 amps. Fuel passing across the fuel pump's armature is subjected to sparks and arcing; this sounds quite dangerous, but the absence of oxygen means that there will not be an explosion!
efi_1-0.pngThe majority of fuel pumps fitted to today’s motor vehicles are fitted within the vehicle’s petrol tank and are referred to as ‘submerged’ fuel pumps. The pump is invariably be located with the fuel sender unit and both units can sometimes be accessed through an inspection hole either in the boot floor or under the rear seat. Mounted vertically, the pump comprises an inner and outer gear assembly that is called the ‘gerotor’. The combined assembly is secured in the tank using screws and sealed with a rubber gasket, or a bayonet-type locking ring. On some models, there are two fuel pumps, the submerged pump acting as a ‘lift’ pump to the external roller cell pump.
