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FUEL PUMP SPEED CONTROL OPERATION [L3 Turbo]

id0140b6102500
• Controls the fuel pump speed control relay according to the fuel amount required by the engine.
• The required fuel amount is determined by the engine speed, the ECT and MAF.
• When the required fuel amount exceeds the fixed amount, the PCM turns the fuel pump speed control relay on.
• The fuel pump speed is switched by the demand fuel injection amount and the battery voltage.
• At cold engine start, the cranking speed may decrease. When the engine coolant temperature is low, the fuel pump speed control relay is turned on during cranking, and fuel flow is promoted.
• At warm engine start, bubbles are easily formed in the fuel. If the intake air temperature and the engine coolant temperature are high, the fuel pump speed control relay is turned on during cranking and the fuel line pressure (low-pressure) is raised.
• The circuit driving the fuel pump switches by the fuel pump speed control relay turning on or off.
When Fuel Pump Speed Control Relay Off

  - Electric current flows from the fuel pump relay to the fuel pump through the fuel pump resistor. Excess load on the fuel pump is reduced because voltage to the fuel pump is reduced by the fuel pump resistor.

When Fuel Pump Speed Control Relay On

  - Electric current flows from the fuel pump relay to the fuel pump through the fuel pump speed control relay. Voltage to the fuel pump flows from the battery because the voltage does not flow through the fuel pump resistor. Due to this, the fuel delivery amount increases by the increase of fuel pump drive force.

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1 | Main relay
2 | Fuel pump relay
3 | Main relay
4 | Fuel pump speed control relay
5 | To PCM
6 | Condenser
7 | Fuel pump unit
8 | Fuel pump resistor
9 | Check connector
10 | To PCM

## Operation Conditions

During cranking
• During cranking, the fuel pump turns on for improved startability.
At low engine speed
• As less fuel is required, the fuel pump speed control relay is turned off.
At high engine speed
• At high engine speed, the fuel pump speed control relay turns on because the required fuel amount increases.