A bad Fuel Pump can directly cause engine misfires because it affects proper fuel delivery. A misfire happens when the air-fuel mixture in one or more of the engine's cylinders doesn't ignite properly, resulting in incomplete combustion. ASE estimates that up to 20 percent of all engine misfire problems reported on high-mileage vehicles are due to inadequate fuel delivery.
Many Fuel Pumps tend to lose pressure, generally about 40-70 PSI depending on the vehicle. When fuel pressure is too low or fluctuates, injectors receive inconsistent amounts of fuel, which can lead to lean conditions within the engine. Running lean, an imbalance of air-fuel ratio giving more air and less fuelling, results in rising chances of misfires and can lead to scorching or knocking of engine.
One of the most common symptoms associated with a bad fuel pump is engine hesitating when accelerating. As an example, when drivers accelerate, a weak or failed pump can’t provide the resultant increase in fuel demand, causing misfires. The 2020 Bosch Fuel Systems Report points out that fully 25% of fuel pump failures show up as engine performance issues, like hesitation, stalling and/or misfires, especially when loaded.
“Fuel delivery issues can accelerate into engine damage very quickly,” said John Davis, an automotive expert at MotorWeek. That's why you need to be mindful of misfires caused by an issue with the fuel pump early. An effective diagnostic step is to test the output of the pump using a fuel pressure gauge. If during operation the pressure dips below the manufacturer’s specifications, then the pump is likely in need of repair or replacement.
The problem gets worse with dirty or blocked fuel filters. When debris obstructs the flow of fuel, the pump has to work harder, which wears it out sooner and also lowers fuel pressure even more. According to the data of the U.S. Department of Energy, a clogged filter can reduce pump efficiency by 15-30%. Changing the filter every 30,000 miles can avoid these problems and ensure even delivery of fuel.
If misfires are the result of a bad Fuel Pump, the Engine Light may also report DTCs of P0300, which suggests random or multiple cylinder misfires. These codes and symptoms such as rough idling or poor acceleration often lead mechanics to pinpoint the fuel pump as the culprit.
In extreme instances, misfires due to lack of fuel could potentially damage other aspects of the fuel system or the engine. Extended misfiring places extra stress on the catalytic converter, which can overheat or otherwise fail, with repair bills topping $1,000 for the average car. Replacing a failing fuel pump when it needs it, minimizes these risks, and keeps the engine running as designed.
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