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Fuel Injection Technical Information
| ELECTRIC IN-LINE FUEL PUMP - The function of the electric fuel pump is to deliver pressurized fuel to the fuel injection system. The ECU activates the fuel pump relay to operate the fuel pump when the ignition switch is in the On or start position. The pumps are designed to match certain flow and pressure specification for the engine application. In TBI applications the fuel pump must supply enough fuel flow for the engine WOT output at 15 to 20 psi. In multi-port applications the fuel pump must be able to supply enough fuel at full engine load to maintain at least 43.5 psi at the fuel rail. At idle the fuel pressure regulator must be able to return the excess fuel to the tank and maintain the required system pressure. Most of the cars prior to 1987 use an in-line external electric fuel pump. |
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ELECTRIC IN-TANK FUEL PUMP - Almost all car applications after 1987 designed their fuel pump assembly inside the fuel tank. The advantage of having the fuel pump in the fuel tank is mainly lower noise, lower potential leakage problems, less mounting sensitivity of the pump with respect to lift of fuel from the tank is minimized. |
| The in-tank pump went through several designs evolving from a simple "pump on a stick" to a complex in-tank fuel sending modules. The new designs combine the high-pressure electric fuel pump, noise isolation and a fuel level sensor into one compact modular package.This new design also helps reducing hydrocarbon emissions. The hot gasoline returning from the fuel system is returned to the reservoir surrounding the fuel pump. By returning the hot fuel to the reservoir heating of the bulk fuel in the fuel tank is avoided, thus reducing the evaporation of the high volatile portions in the fuel. At present all fuel tank modules are designed and serviced as a complete unit. If the pump or fuel level sensor fails the entire unit will have to be changed. |
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| FUEL PUMP INLET FILTER - The function of this filter is to eliminate any impurities that might harm the fuel pump. In the in-line fuel pump type this filter is external to the fuel tank and is in a replaceable cartridge filter. In the in-tank fuel pumps the fuel filter is in the form of a sock and is directly attached to the pump in the "pump on a stick" version and attached to the fuel pump module in the module version. |
| MAIN FUEL FILTER - The function of this filter is to eliminate any contaminants after the fuel pump. These are either small enough to pass through the fuel filter of the pump inlet or are generated by the fuel pump. |
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| This fuel filter is also of the cartridge type but is designed to sustain much higher fuel pressures that the fuel pump inlet filter. |
| FUEL PRESSURE REGULATOR - Fuel system pressure is maintained by the regulator, while excess fuel is returned to the fuel tank. The regulator consists of two chambers separated by a diaphragm assembly. On the fuel side of the diaphragm a throttling valve is employed to expand or restrict fuel flow as the fuel pressure fluctuates. The other side contains a spring with an adjustment screw that is set at the factory for correct system pressure and flow. This chamber is connected to the intake manifold in MPFI systems to reference the vacuum in the manifold during engine operation. This pressure reference is required to maintain a constant differential pressure across the metering orifice of the fuel injector. |
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