Generally speaking, a fuel pump cuts out at higher speeds due to either low fuel pressure or an impending problem with the pump itself. A modern fuel pump supplies fuel pressure in a small window from the governing of the vehicle in question, roughly estimated between 40 to 60 psi. At higher speed, the engine requires more fuel to maintain power and efficiency. If that quantity of fuel is not successfully provided by the pump, then it may begin to cut out. This can result in stalling or failure of power.
One major common complaint with regard to a fuel pump cutting out at high speeds is related to a blocked fuel filter. The fuel filter burdens with particles, and over time, it limits the fuel flow, especially when the engine is most stressed at higher speeds. Bosch, a major automaker's parts supplier, recommends replacement of the fuel filter every 20,000 to 40,000 miles as particles in the fuel build up and clog the filter, therefore impeding the normal flow of fuel. Depending on the driving conditions, they claim that up to 30% of fuel pump efficiency can be lost due to a clogged filter; the pump then has a hard time supplying sufficient fuel at high speeds.
Another possible cause is a failing fuel pump relay or an electrical problem. The relay basically controls the flow of current into the pump. When faulty, it can result in intermittent losses of power to the pump, particularly when the car is moving faster. In fact, Ford recalled over 50,000 vehicles in 2018 due to fuel pump relay issues that caused fuel pumps to intermittently cut out during driving at high speeds and cause engines to stall.
The fuel pressure regulators are also very important in maintaining proper fuel pressure. A faulty regulator will not sustain the pressure once the car is at higher speeds, hence starvation kicks in. Depending on the car, the replacement cost ranges between 150 and 300 dollars, which, though expensive, will deter fuel delivery problems in high-speed driving.
Sometimes, it's the fuel pump that is malfunctioning due to wear and tear. The life of a fuel pump is usually estimated to be around 100,000 to 150,000 miles, but running on fumes or very low-quality fuel can easily shorten this. When the pump approaches the end of its service life, it sometimes cannot maintain proper fuel delivery, especially when the engine is under more power demand. It shows that according to the AAA, issues with the fuel system, like failing fuel pumps, account for nearly 7% of roadside breakdowns.
Running on low fuel is also likely to make the pump overheat, especially in high-speed driving. The fuel in the tank cools the pump, so when levels get too low, the pump may overheat and cut out. For example, General Motors suggests keeping at least a quarter tank of fuel in the tank to ensure the pump is submerged and properly cooled, especially for long-distance driving or at high speeds.
Thirdly, a weak fuel pump will not be able to deliver proper pressure to maintain a constant, correct fuel-to-air ratio. In that case, the engine would run lean at high speed. The lean state of the mixture, meaning too little fuel in it, might be the reason behind engine misfiring or power loss, giving a feeling as if the pump cuts out.
Fuel Pump explains how to service a fuel pump and offers troubleshooting guidance for common problems.