Ameer Randolph
Some cars have two fuel pumps, which means there are two fuel pump relays, each with its own fuse. One pump is closer to the fuel tank, and the other is closer to the engine. When you turn the key to start the car, the ECM grounds the Fuel Pump Relay #1, closing it and sending 12 volts to the fuel pump motor for 2 seconds. If the engine is running, the ECM will close the fuel pump relay, sending 12 volts to the fuel pump motor continuously. If the fuel pump relay fails, there is an oil pressure switch that will close and send 12 volts to the fuel pump motor when the oil pressure reaches 4 psi or more.
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What You'll Learn
Fuel pump relays and fuses
The fuel pump relay plays a critical role in the "start cycle" of the combustion engine. It provides a small but consistent voltage to the fuel pump, ensuring its proper functioning. In some cars, there may be two fuel pump relays, each fused separately in the i/p fuse block, with an additional fuel pump fuse in the underhood fuse block.
It is important to regularly inspect and maintain the fuel pump relay as it can be susceptible to dirt and debris, especially when located in the engine bay where it is exposed to heat. Cleaning the relay is a simple maintenance task that can help ensure optimal performance. In the event of a faulty relay, it can be replaced, with costs typically ranging from $90 to $150.
Fuses are another critical component of the fuel pump system. They protect the electrical circuit by melting and breaking the circuit if there is an excessive current. Fuses are designed to be easily accessible and replaceable, and it is important to ensure they are in working order.
In some cases, the fuel pump may be integrated into the fuse box, with the Airbag Control Unit (ACU) responsible for shutting down the fuel pump in the event of an accident. However, this setup has raised safety concerns, as the PCM may not be able to shut off fuel flow during pressure loss or a collision.
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ECM and fuel pump motor
In cars, the ECM (electronically commutated motor) is an integral part of the fuel pump system. When the car key is turned to start the engine, the ECM grounds the Fuel Pump Relay #1, which closes and applies 12 volts to the fuel pump motor for 2 seconds. If the engine is cranking or already running, the ECM will continuously apply 12 volts to the fuel pump motor.
The ECM motor is a highly efficient component that eliminates rotor losses and achieves higher efficiency at full load, reduced speed, and torque loads. It does not require a magnetic field to function, which reduces the time lag experienced by standard motors, resulting in increased efficiency. Additionally, the ECM motor has permanent magnets, an electronic starting circuit, and no slip, which further enhances its efficiency by reducing heat and friction.
In the context of the fuel pump system, the ECM plays a crucial role in ensuring the reliable operation of the fuel pump motor. By applying the required voltage, the ECM enables the fuel pump motor to function optimally, providing the necessary fuel supply for the engine.
Some vehicles, such as those with GDI (Gasoline Direct Injection), may have two fuel pumps: a low-pressure or lift pump and a high-pressure pump. In such cases, the ECM's role in controlling the fuel pump motor voltage becomes even more critical, as it ensures the proper functioning of both pumps.
It is important to note that while ECM motors offer improved efficiency, they are not a cure-all for pump inefficiencies. The pump itself and its design also play a significant role in overall system efficiency. However, by combining an ECM motor with a well-designed pump, significant energy savings and performance benefits can be achieved.
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Oil pressure switch as a backup
In a car's fuel system, the oil pressure switch serves as a backup mechanism to the fuel pump relay. When the ignition key is first turned on, the Engine Control Module (ECM) grounds the Fuel Pump Relay #1, allowing 12 volts to be delivered to the fuel pump motor for 2 seconds. If the engine is cranking or running, the ECM will continuously apply 12 volts to the fuel pump motor.
The oil pressure switch comes into play as a backup if the fuel pump relay malfunctions. When the oil pressure reaches 4 psi or more, the switch closes, completing the circuit and providing 12 volts to the fuel pump motor. This backup mechanism ensures that the fuel pump continues to operate even if the primary relay fails.
The oil pressure switch typically has two wires: an orange wire and a red wire. Shorting the orange wire to the red wire will activate the fuel pump motor. However, caution is required when handling the orange wire as it remains live at all times.
While the oil pressure switch serves as a backup, some have questioned its effectiveness and safety. In certain cases, it has been reported to cause issues, leading to concerns about potential engine damage. It is recommended to consult a professional or refer to the vehicle's service manual for specific information regarding the oil pressure switch and its role in the fuel system.
The oil pressure switch is not a standard feature in all vehicles, and its presence may vary depending on the make and model of the car. It is generally advised to refer to the vehicle's documentation or seek advice from a qualified mechanic to understand the specifics of the fuel system and any backup mechanisms in place.
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GDI engines and multiple pumps
GDI engines, or Gasoline Direct Injection engines, inject highly pressurised fuel directly into each cylinder's combustion chamber. This technology has been used since the 1990s and has become increasingly popular due to its ability to meet stricter emissions and fuel economy standards. GDI engines require more highly pressurised fuel, which is where high-pressure GDI fuel pumps come in. These pumps are responsible for creating enough pressure so that the fuel fully atomises.
GDI engines typically have a low-pressure or lift pump and a high-pressure pump. The low-pressure pump is located in the fuel tank and supplies fuel to the high-pressure pump, which is typically driven by the camshaft. The high-pressure pump then generates the high pressures needed and delivers the high-pressure fuel to the fuel rail. The amount of pressure generated in the fuel rail is determined by an ECM-controlled fuel volume solenoid or a PCM-controlled integral fuel regulator, which is typically part of the mechanical pump.
The number of GDI pumps in a vehicle depends on the engine configuration. Most four-cylinder vehicles have one GDI pump, while V6 and V8 engines will likely have two pumps, with one pump for each bank of fuel. The high-pressure GDI fuel pumps require enough power that they need to be driven by the engine, and they are designed to keep the fuel pump closely aligned with the engine to ensure it always gets the right fuel pressure.
One potential issue with GDI pumps is that they are known to leak gasoline into the engine when they fail, which can cause fuel trim issues or engine failure due to oil dilution. Therefore, it is important to inspect and change the oil after a pump failure. Additionally, the most common issue with GDI fuel systems is carbon buildup in the intake and on the backs of the intake valves, which can be caused by incomplete combustion.
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Mechanical fuel pump fuses
A mechanical fuel pump fuse is essential to shut down the current to the pump. If you remove the pump, you will see a small fuse behind it. This fuse is not the same as the one in the fuse block; it is a special mechanical fuse.
In a car, there are two fuel pump relays, each fused separately in the I/P fuse block. There is also a fuel pump fuse in the underhood fuse block. When you first turn the key to run, the ECM will ground the Fuel Pump Relay #1. The relay closes, and 12 volts is applied to the fuel pump motor for 2 seconds. If the engine is cranking or running, the ECM will close the fuel pump relay, and 12 volts will be applied to the fuel pump motor all the time.
As a backup, if the fuel pump relay fails, there is an oil pressure switch that will close and apply 12 volts to the fuel pump motor when the oil pressure reaches 4 psi or more. This is an important safety feature to prevent the engine from running without a properly functioning fuel pump.
Some vehicles with GDI (Gasoline Direct Injection) engines have two fuel pumps: a low-pressure or lift pump and a high-pressure pump. One of these pumps is run by the engine, while the other runs on 12 volts. This configuration ensures that the engine receives a consistent supply of fuel at the required pressure.
If a fuel pump fuse blows, it could be due to a few reasons. One possibility is that the fuel pump is drawing excessive amperage due to being worn out or overheating. This can be caused by a faulty or old fuel pump. Another possibility is a short to ground in the wiring between the inertia switch and the fuel pump, which could be due to broken wire insulation or the fuel pump wires touching inside the harness.
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Frequently asked questions
There are two fuel pump fuses in your car because there are two fuel pump relays, and each one is fused separately. One fuse is in the i/p fuse block, and the other is in the underhood fuse block.
If one of the fuel pump fuses blows, you can try replacing the fuse and the fuel pump relay. If the new fuse also blows, there may be an issue with the fuel pump itself, the wiring, or the PCM (powertrain control module).
Your car may have two fuel pumps if it has GDI (Gasoline Direct Injection). In this case, there will be a low-pressure or lift pump and a high-pressure pump. One of the pumps will be run by the engine, while the other will run on 12 volts.
The location of the fuel pump fuses can vary depending on the car model. They are typically located in the fuse box, which may be in the engine bay or inside the car, often below the steering wheel. Refer to your car's manual or seek advice from a mechanic to locate the specific fuses.
A faulty fuel pump fuse may cause the car to not start or run erratically. The fuse may blow due to excessive amperage draw by the fuel pump, which could be a result of a faulty or worn-out fuel pump, or an electrical short circuit.
