The Failing Fuel Pump disrupts the flow rate of fuel to the engine leading to rough idle. Currently, we are moving toward injectors with a certain type of fuel pressure, between 35/65 PSI, that will guarantee the proper air-fuel mixture ratio. If the fuel pump fails to deliver this constant pressure, the engine will misfire, not burn fuel evenly and the engine will run irregularly at idle.
A failing pump usually result in fuel starvation. This inadequate fuel supply leads the engine to run lean: a mixture with more air than gasoline. With an unbalanced fuel signal, combustion can be compromised, often causing roughness or sputtering at idle. According to a 2021 study, cars with fuel pumps providing less than half of the pressure they need are twice as likely to encounter rough idle and stalling.
Another factor that can lead to rough idling is an electrical problem with the fuel pump system. The pump is reliant on a stable 12v power to work effectively. Intermitent power loss affecting regular fuel supply can be caused by corroded connectors, frayed wires or a fauilng relay. If voltage is an issue and the pump does not receive power consistently, it can be diagnosed with a multimeter test at the pump terminal.
And clogged fuel filters typically compound those problems. The filter, which needs to be changed every 20,000 to 30,000 miles, can restrict fuel flow to the pump, causing it to work harder and resulting in erratic performance. Changing a clogged filter — which usually costs $20 to $50 — is a cheap proactive way to protect the pump and ensure the car idles smoothly.
One real-world example illustrates this issue. In 2022, we encountered an idling dilemma in a compact SUV, which had a rough idle and constantly stalled out at traffic lights. Diagnostic tests showed the fuel pump was only doing 20 PSI, which was below the specs needed for the engine. The engine then idled smoothly after changing the pump, fuel efficiency increased by 15%.
As Henry Ford reportedly said, “Most people spend more time and energy going around problems than in trying to solve them.” Fixing a bad fuel pump is important to avoid other problems, such as potential damage to your catalytic converter or other engine components. And while replacing a failed pump will run $200 to $1,000 or more, depending on the car, it’s done for peace of mind.
Need to learn more about how to maintain your fuel pump and trouble shoot it? Head on over to Fuel Pump.