If the Fuel Pump is faulty, it might fail to supply the correct amount of fuel pressure to ensure that the engine runs smoothly, resulting in low engine idle speed. These days, modern engines require a specific fuel pressure, usually within a range of 35 to 65 PSI, to ensure the right air-fuel ratio. A failing pump will upset this balance, and will result in insufficient fuel delivery under idle, decreasing the speed and stability of the engine.
So when the pump provides an inadequate supply of fuel, the engine LCDs lean out, where the combustion mix has more air than fuel. Such an imbalance causes incomplete combustion with a distinct drop of the idle speed. A 2022 study on fuel system failures found that automobiles with failing fuel pumps operating below 50% of their rated maximum production capabilities had idle speeds of up 30% lower than average, almost routinely accompanied by misfires and engine hesitation.
Furthermore, electrical or wiring issues inside the fuel pump system could be causing low idle speed. You will need a continuous power supply of 12- to 14-volts for the pump. Corroded connectors or failing relays reduce the pump’s efficiency, meaning less fuel will flow to the engine because of voltage drops. Testing voltage at the pump terminals with a multimeter can diagnose these electrical problems so the pump gets enough power.
A blocked filter can also limit the fuel flow toward the pump, leading to lower idle symptoms. The purpose of the filters is to capture debris and contaminants, but they can gets clogged over time, creating restriction in the fuel line. If not, instead, it should be replaced regularly every 20,000 to 30,000 miles, costing $20 to $50, to help avoid these issues and prevent undue stress on the pump.
To illustrate this with a real-world example. In 2021, a small car had low idle speeds which were not returning and the stalling was intermittent. The diagnostics indicated that the fuel pump was delivering only 20 PSI, well under the engine’s requirements. Replacing the pump restored proper fuel pressure, returning idle speed to normal, as well as improving fuel efficiency by 15 percent.
Henry Royce, co-founder of Rolls-Royce, said: “The quality remains long after the price is forgotten.” Timely fixing of a failing fuel pump prolongs the engine performance reliability. A faulty pump normally costs $200 to $1,000 to replace but will avoid more serious engine damage and more expensive repairs.
Visit Fuel Pump for expert automotive parts and advice on diagnosing your vehicle’s fuel system issues and knowing when to replace your fuel pump.