A car may stutter or hesitate when accelerating due to a bad fuel pump because this component is responsible for supplying fuel to the engine at the correct pressure. Inconsistencies in the delivery of fuel, brought about by a faulty fuel pump, disrupt the performance of the engine. A report from the National Institute for Automotive Service Excellence (ASE) claims that 5-10% of all problems related to poor engine performance can be traced to the fuel pump. Hesitation, stalling, or the inability of the car to accelerate, especially under load when more fuel is needed, may also be some of the other effects.
When a fuel pump is not working correctly, it cannot support the correct fuel pressure inside, which is usually between 30 and 60 psi for most vehicles, depending on the type of engine. Due to this, the engine may not get the right amount of fuel to run smoothly, which can be manifested by stuttering or misfires. For instance, a 2010 Honda Accord may develop stutter at less than 35 psi fuel pump pressure, where poor fuel atomization can occur and cause rough idling and hesitation upon acceleration.
The fuel pump itself can also be a potential cause of stutter, which might result from possible debris, corrosion, or wear and tear over time. When a pump starts failing, it may work on occasion, but drops in pressure cause an engine to sputter-a lot-especially on uphills or when a heavy throttle is required for highway speeds. A prime example of this was found with a 2016 Chevrolet Silverado that had stuttering symptoms from a clogged fuel filter, making the fuel pump work harder until eventually it completely failed.
Additionally, a malfunctioning fuel pump can disrupt the fuel/air mixture ratio. If the fuel pump is not able to provide the required quantity of fuel, then the engine’s computer may act to adjust the air-fuel mixture accordingly. The result is an engine that is running too lean-in other words, not enough fuel-which causes the stuttering sensation. This is most evident when quick acceleration or high speeds are involved.
When the car stutters, it can be that the fuel pump is struggling to meet the demand and the engine loses power for some time. Most fuel pumps last a long time-between 100,000 and 150,000 miles-but over-usage, low-quality fuel, or contamination can easily shorten that time. This problem has to be dealt with as quickly as possible before it completely ruins the motor and other parts of the fuel system.
Sometimes, diagnostic tools can report low fuel pressure, which is a sure sign that the fuel pump is the likely culprit behind the stutter. Other symptoms such as engine misfires, poor starting, or bad fuel economy will also help confirm a faulty fuel pump.
For a detailed guide on how to diagnose and replace a faulty fuel pump, refer to Fuel Pump.