If fuel pump pressure declines, engine output will likewise suffer promptly. In the case of an engine, most operate optimally when fuel pressure is between 40 to 60 psi. Even a simple 10% drop in fuel pressure can result in problems like rough idling, stalling, or hard starting. If there is not enough pressure, the engine is deprived of fuel/air mixture and can start to misfire or hesitate under acceleration. Just 5 psi below the recommended level causes a measurable loss of engine power - up to 15%.
The fuel injectors need a steady supply of pressure in order to atomize the droplets of fuel being sprayed into the combustion chamber. If this pressure is disturbed, it may create a situation in which the right amount of fuel may not be delivered to the injectors which can result in incomplete. In fact, by 20%, in such severe cases, the engine can stall, particularly under significant loading or in high-speed operation. In one high-profile case from 2016, faulty fuel pumps that led to a drop in pressure were responsible for a significant automotive recall, stifling of the automotive systems.
When fuel pump pressure drops, fuel economy takes a hit. This is why the engine starts running richer (burning a bit more gas to achieve the same performance, though) as it has to overcome this mounting deficiency of fuel demand. As a result, fuel consumption can increase by 10-20%, and with it costs to the driver. With time, this imbalance can accelerate the deterioration of engine parts like pistons and valves prematurely by several thousands mile.
Less fuel pressure will result in fuel pump overheating also. Fuel pumps count on a consistent fuel flow for cooling and when pressure is low, the pump can overheat leading to premature failure. This is especially prevalent when the vehicle has been driven on a nearly empty fuel tank. So if you have a low level of fuel then studies suggest this can reduce the lifespan of a fuel pump by up to 30% particularly in hotter climates.
Also, extended periods of low fuel pressure can ruin the catalytic converter. When an engine is running with excess fuel, with not enough oxygen to burn it all before leaving out the exhaust, unburned fuel enters the exhaust system where it can ignite and cook the catalytic converter. This alone is a very expensive result of allowing the symptom of fuel pressure problems to linger without taking action as replacing a catalytic converter can cost you anywhere from $1,000 up to $2,500+.
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