In a fuel pump,… Fuel pumps are designed to work in one direction that helps maintain an uninterrupted & uniform supply of gas from the tank to engine. You cannot just run the Pump backwards again, because the Fuel Pump contains check valves and impellers that are only designed to operate in one direction. These are long-travel type components by design that want to push fuel forward, not be compressed sideways and reversals can result in considerable mechanical resistance which adds impeller load [inefficiency] as well increases the chance of pump damage. Testing shows that trying to reverse the operation of a fuel pump can reduce its performance by almost 50%, causing incorrect engine-performance-ruining fuel-pressure levels.
Electric Fuel Pumps - An electric motor drives an impeller in a much similar way to centrifugal pumps, which creates pressure that moves fuel in one direction typically-used modern cars. The design helps avoid backflow and guards the engine against fuel starvation, which can cause stalling or misfiring. Over the years, engineering studies proved that reversing an electric fuel pump can wreck havoc in fuel pressure which is more than sufficient to drop its baseline value of 40-70 PSI usually down towards very close or even zero - not enough to sustain proper injection on all cylinders. This fall can wreak havoc on vehicles which need a steady fuel pressure for safe performance, including large engines and those augmented with turbochargers.
Reversing operation in mechanical fuel pumps, especially those fitted to older carbureted engines can lead to the diaphragm and check valves anti-draining being out of alignment with one another as they are calibrated for unidirectional flow. Trying to spin these pumps in reverse is likely to stress fine internal parts, potentially causing a failure. Consumer Reports states 8 percent of fuel pump failures in classic cars are �due to installation problems or mechanical abuse, such as trying to backflow the fuel.
As automotive engineer Carroll Shelby once said, “The answer is in the details. In fuel system design terms, this meticulous return on attentiveness ensures that pumps supply fuel air-tightly and constantly — in the right direction. Maintaining the Fuel Pump as intended not only keeps a typically 100,000- to 150,000-mile life on the pump but also guards against any engine disturbances due to poor or irregular fuel delivery than can ultimately degrade overall vehicle performance and reliability.