A variety of fuel pump control circuits and controls have been used over the years. The following basic methods are:
• ON/OFF Control by Fuel Pump Switch.
• ON/OFF Two Speed Control with a Resistor.
• ON/OFF Two Speed Control with Fuel Pump ECU.
• ON/OFF Three Speed Control with Fuel Pump ECU.
The most accurate way of determining the type of fuel control circuit is to look up the circuit in the appropriate EVVD.
The following describes the basic methods of fuel pump control. An essential point to remember is that the fuel pump operates only when the engine is cranking or running.
ON/OFF Control by ECM
The following is an explanation of how the fuel pump circuit is activated. Engine Start
When the engine is cranking, current flows from the IG terminal of the ignition switch to the L1 coil of the EFI main relay, turning the relay on. At the same time, current flows from the ST terminal of the ignition switch to the L3 coil of the circuit opening relay, turning it on to operate the fuel pump. The fuel pump is now supplying fuel to the fuel injection system.
Note: The circuit opening relay in this example is ground side switched.
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