XC70 L5-2.5L Turbo VIN 59 B5254T2 (2003)
Fuel Pressure Regulator: Description and Operation
Fuel Pressure Regulation (Only Vehicles With Demand Controlled Fuel Pumps)
General
Fuel pressure regulation for demand controlled fuel pumps (DECOS-DEmand COntrolled fuel Supply) means that the fuel pressure is controlled
steplessly by varying the output of the fuel pump. The design of the system allows a greater maximum pressure (approximately 6.5 bar) in the fuel pump.
This pressure is used in extreme situations, such as heavy engine load for example.
The following components are used for fuel pressure regulation:
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engine control module (ECM)
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the fuel pump control module
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a fuel pressure sensor with a fuel temperature sensor
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a fuel pump (FP) with a by-pass valve.
The time taken for the engine start procedure can be reduced by rapidly increasing the pressure in the fuel rail when the engine control module (ECM)
receives a signal about the position of the ignition switch from the central electronic module (CEM).
The engine control module (ECM) is better able to calculate the injection period because the signal from the fuel pressure sensor gives information about
the fuel pressure. This particular improves the cold starting characteristics of the engine.
The advantages of varying the output of the fuel pump so that it is not always at full power are:
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the total power consumption of the fuel pump (FP) is reduced, reducing the load on the power supply system
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the service life of the fuel pump (FP) is increased
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fuel pump noise is reduced.
Control
The engine control module (ECM) calculates the desired fuel pressure. A signal is then transmitted to the fuel pump control module indicating the
desired fuel pressure. Serial communication between the engine control module (ECM) and the fuel pump control module is used to carry the signal. The
fuel pump control module then operates the fuel pump unit to obtain the desired pressure using a pulse width modulation voltage on the ground lead. The
fuel pump (FP) can be controlled steplessly by changing the pulse width modulation (PWM) signal. Only that pressure which is required at that specific
time will then be released to the fuel rail/injectors. The value of the pulse width modulation (PWM) signal is a measurement of the operational load of
the fuel pump (FP) (% duty, 100% = maximum pressure).
