An accelerator pump is a component on a carburetor. It is commonly found on many older vehicles that are equipped with carburetors. The accelerator pump is responsible for providing the momentary additional fuel needed under heavy acceleration conditions. When the pedal is suddenly pressed, the throttle will suddenly open, immediately adding additional air for additional power. That additional air requires additional fuel, especially in the precise moments after the throttle is opened, this is the fuel the accelerator pump provides. When the throttle is rapidly opened, the accelerator pump will squirt a small amount of fuel into the throat of the carburetor so that the engine can continue running smoothly under increased load. Usually when the accelerator pump is having issues, it will display a few symptoms that can alert the driver that there may be a problem that should be inspected.

Rough acceleration

One of the most common symptoms that the accelerator pump is having a problem is rough or sluggish acceleration. The accelerator pump is supposed to provide additional fuel needed during acceleration. If there is any problem with the pump, then there will be a problem in the fuel mixture during acceleration. Usually, a faulty accelerator pump will result in a momentary lean condition, which can result in rough or sluggish acceleration, and even misfires.

Engine sputtering or stalling

Another symptom of a faulty accelerator pump is engine sputtering or stalling. The sputtering is caused by the lack of fuel that is supposed to be provided by the accelerator pump when throttle is rapidly pressed. In more serious cases of accelerator pump failure, rapidly pressing on the gas may cause the engine to stall, again due to the lean condition that can be created when the accelerator pump is not working.

A faulty accelerator pump will typically produce a noticeable effect on the engine performance when it fails or is having a problem. If you suspect that your accelerator pump may be having an issue, have the vehicle diagnosed by a professional technician, such as one from YourMechanic. If necessary, they will be able to replace your accelerator pump for you and restore proper performance to your vehicle.

This article originally appeared on as Symptoms of a Bad or Failing Accelerator Pump and was authored by Eduardo Ruelas.

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