Why Does My Car Struggle to Start with a Bad Fuel Pump?

A failing Fuel Pump will greatly affect a vehicle’s ability to start, as it carries fuel from the tank to the engine at the proper pressure. Most Fuel Pumps run around 30-80 PSI depending on design for that engine, so if a pump can not achieve enough pressure you’ll get either hard starts or no start at all, since that engine won’t be getting the proper volume of fuel for combustion.

A malfunctioning Fuel Pump can fail to adequately provide fuel to the engine due to a number of factors, such as component wear and tear, damaged parts or contamination. The fuel filter can clog with time or fuel pump relay can fail, thus a insufficient supply of fuel to run. In fact, more than 40% of breakdowns associated with the fuel system according to a report from Consumer Reports 2019 were caused by defective Fuel Pumps, and many of these failures would typically cause difficulty in starting the car and in the cold start, specifically.

For instance, a worn-out Fuel Pump may not be able to deliver sufficient pressure level to pump fuel through the system properly. This also causes the engine to be starved for fuel at startup, as everything from the tank to the fuel rails need primed and pressurized. A weak Fuel Pump will fight to build this pressure quickly enough, resulting in the engine not being able to start. At times, the engine may crank but not fire up, or may start after multiple tries.

Inconsistent delivery of fuel can also be caused due to malfunctioning of Fuel Pump. If the pump intermittently fails to deliver fuel at the correct pressure, the engine will stall or struggle to start if it is not getting the right mixture of air and fuel. According to a2017 study by AutoWeek, 20 percent of all engine stalls can be attributed to Fuel Pump related failures, often due to corrosion or contamination of the fuel pump assembly.

Normally, in addition to fuel supply issues, the Fuel Pump is often linked in conjunction with the vehicle’s fuel pressure regulator which regulates the flow and pressure of the fuel. If the pump fails to deliver fuel at the correct pressure, the regulator cannot compensate sufficiently, and that, in turn, will make it even more difficult for the engine to start.

Hearing experts such as veteran wrench Scotty Kilmer often note a bad fuel pump can also create vapor lock, which they say is especially prevalent in older vehicles. Vapor lock happens when your fuel vaporizes due to too much heat, which can prevent fuel from reaching the engine. This can make the car stutter or not start at all, especially after refueling or in high-heat conditions. In fact, vapor lock is more prevalent in vehicles with over 100,000 miles, especially when the Fuel Pump had not been properly maintained, according to AAA.

A fuel pump failure can even activate warning lights on the car’s OBD-II system, signaling a loss of fuel pressure. For example, the P0087 (Fuel Rail/System Pressure Too Low) DTC codes can point directly to problems with the Fuel Pump and are typically a good early warning sign of the impending failure of the pump.

In short, a car/vehicle will have trouble starting with a bad Fuel Pump because the engine does not receive the right kind of fuel delivery (be it low pressure or sporadic fuel feeding to the engine, or lack of pump/placing altogether). IMPORTANT: Regular maintenance and replacement of a faulty Fuel Pump will keep the obstruction of starting the engine to a minimum and will continue to keep the engine running smoothly.

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