Fuel Pump Continuity: Why It's Important For Electric Vehicles

Whether or not an electric fuel pump should have continuity is a highly debated topic. Some sources claim that there should be some continuity, while others argue that there should be none. Most fuel pumps draw several amps and should ohm out with a fairly low resistance. However, if there is a short between windings in the motor, it can cause higher than normal current and more heat. This can result in the need for a new fuel pump. It's important to regularly replace fuel filters and inspect the in-tank sock to ensure it is not clogged or collapsed, as this can cause the fuel pump to draw more current than usual. While some sources suggest that a fuel pump with a draw of 6 amps should have a resistance of 2 ohms at 12 volts, others claim that the resistance should be higher, around 100 ohms or more. It is recommended to use a meter to measure the resistance and current flow to determine the condition of the pump accurately.

Electric fuel pumps should have some resistance

A fuel pump that draws 6 amps should have a resistance of 2 ohms at 12 volts. Most fuel pumps draw several amps and should ohm out with a fairly low resistance. The more amps a pump pulls, the less the resistance across the terminals. According to Ohm's law, at 12v, a 10-amp draw would show only 1.2 ohms.

It is recommended to have a common ground for the pumps and to use a thick enough wire from the relay to the pump. A 10 AWG wire is commonly used for this purpose. Additionally, it is important to ensure that the fuel filter is not clogged or collapsed, as this can cause the fuel pump to draw much more current than usual.

When measuring the resistance of a fuel pump, it is important to set the meter to measure resistance between the positive and negative terminals. A reading of at least 100 ohms across the + and - terminals is recommended to prevent excessive heat generation.

A short between windings in the motor can cause high current and heat

Electric fuel pumps should have continuity between the positive and negative terminals. This is because the fuel pump draws several amps and should have a fairly low resistance, which can be measured with a continuity meter.

When a short occurs, a large amount of motor winding is bypassed, and the increased current flow can lead to excessive heat. This heat can cause rapid deterioration of the winding insulation, reducing the lifespan of the motor. Therefore, it is important to identify and address any shorts or insulation breakdowns to prevent further damage.

To identify a short, a resistance measurement can be taken. A healthy fuel pump should have at least 100 ohms across the positive and negative terminals. If the resistance is lower than this, the pump may be faulty and drawing much more current than usual, leading to excessive heat. In this case, the fuel pump may need to be replaced.

A high-amperage pump will have lower resistance

Electric fuel pumps should have continuity between the positive and negative terminals. This is because there should be some resistance, not a direct short. The more amps the pump pulls, the less the resistance across the terminals. For example, according to Ohm's law, at 12V, a 10-amp draw would show only 1.2 ohms. Most fuel pumps draw several amps and should ohm out with a fairly low resistance.

Mechanically, the load on the pump may have increased, causing higher amperage. This could be due to increased bearing loading, causing the outside diameter of the bearing to cool and over-compress. It could also be due to incorrect lubrication levels, with too much lubricant in the bearing. Additionally, the starting procedure could be an issue, such as starting a radial flow pump with the discharge valve open, or an axial flow pump with the discharge valve shut.

Electrical issues can also cause higher amperage in pumps. For example, there could be a current imbalance due to a short in the motor windings or an imbalance in voltage. A site power factor change can also affect the power factor and circulate higher apparent power through the system.

It is important to note that each electric motor is wound differently depending on its design, so there is no exact measurement for the resistance of a high-amperage pump. However, as a general rule, a high-amperage pump will have lower resistance compared to a low-amperage pump.

A fuel pump that draws 6 amps should have a resistance of 2 ohms at 12 volts

In the case of a fuel pump, the voltage is 12 volts, and the current (or amperage) is 6 amps. Multiplying these values together gives us a resistance of 2 ohms. This calculation assumes that the fuel pump is drawing a constant current of 6 amps, and that there are no other factors affecting the circuit.

It is important to note that the resistance of a fuel pump can vary depending on various factors, such as the design of the motor and the presence of any parasitic losses. Additionally, the resistance of a fuel pump can change over time due to corrosion or other factors. Therefore, it is always a good idea to measure the resistance of a fuel pump using a continuity meter or a similar device to ensure that it is within the expected range.

According to some sources, most fuel pumps should have a fairly low resistance, and a measurement of 100+ ohms may indicate an issue with the fuel pump or the circuit. However, it is worth noting that the resistance of a fuel pump at rest can be different from the resistance while the pump is running. Therefore, it may be necessary to measure the resistance under different conditions to get an accurate understanding of the pump's performance.

A high-resistance pump may still work

A fuel pump should light up the continuity meter, and it should have low resistance. However, a high-resistance pump may still work. For instance, a user on horsepowerjunkies.com shared that their Holley blue pump had 120 ohms across the terminals, while an Aeromotive A1000 had 160 ohms, and both worked.

Another user on the same forum shared that their Walbros pumps measured 0.8 ohms each, which is closer to the expected resistance. They also mentioned that if the pump were run longer, the resistance would likely drop further due to corrosion on the contacts.

On the ScannerDanner forum, a user questioned how their Kubota BX25 tractor's fuel pump could be functioning despite high resistance (2.75 M ohms) and an unusual continuity reading. The user was unsure if the gelled diesel or the pump was causing the issue and sought assistance in interpreting the readings.

It is important to note that while a high-resistance pump may function, it can also lead to higher than normal current and more heat. This can cause the relay to get extremely hot. Therefore, it is recommended to check for any issues such as a clogged fuel filter or a collapsed in-tank sock, which can cause the fuel pump to draw more current than usual.

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