A fuel pump has a direct impact on starting power since it supplies the first fuel required to ignite the engine. In most fuel-injected engines, the fuel pump increases the pressure of fuel lines to 30-60 psi before ignition so that from the very beginning, the correct mixture of air and fuel would be provided to the engine. If the fuel pump has to work harder for this sort of pressure, then that could mean longer cranking times where the engine cranks but the flow of fuel is just not there. Often, this serves as a sign of a weak pump-inconsistent delivery of fuel, especially on cold starts.
Low fuel pressure also makes the engine fail to sustain initial idle and stall-out as the pump cannot support the necessary pressure. Statistics reveal that 15% of start-up problems in vehicles with high mileage are indeed traced back to inefficiencies in the fuel pump. The problem occurs in engines with over 100,000 miles since the wear and tear of pumps render them incapable of supplying the necessary rate of fuel delivery for a healthy start.
Fuel pumps running on low levels of fuel more often stand a greater chance of compromising starting power. Running a fuel tank at less than a quarter full can result in overheating of the pump because fuel is normally used to cool it. If that were to happen for a very long period, it would reduce the life span of such a pump by as much as 30%, resulting in a drop in pressure of fuel when the engine is started hence affecting its performance. Pro car technicians say that at least a quarter of it must be filled up to avoid overloading of the fuel pump.
Other symptoms that are related to a defective fuel pump that would influence the power of starting-up would be sputtering and intermittent stalling shortly after ignition. These symptoms may be signs that the pump is not always supplying fuel continuously to the engine. According to mechanics, addressing these symptoms early will avoid expensive repair to the engine due to lean fuel mixtures or incomplete combustion at startup.
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