The fuel pump will not be able to produce a sufficient amount of fuel pressure to the engine, and it sure can cause you hard starting problems when the fuel pump relay goes bad. The fuel pump relay sends electrical power to the fuel pump, which in turn runs to pressurize the system. If the relay fails it will cut off or only give one half a cycle of power to the fuel pump and the cars computer may have delayed the fuel delivery. The fuel system generally needs 40-to-60 psi to start the engine reliably. If the relay is failing, it enables fuel, but with a longer delay to get this pressure, hence hard starting is a common symptom.
This prevents the fuelpump to prime the system when the ignition is turned on if thereis a problem with relay engagemant. As this power is affected intermittently, the fuel pump will at times have to be tried numerous times to help start the vehicle. According to technicians, 10-15% of hard starting issues are connected with problems in the fuel system electrical and many times these situations revolve around a bad fuel pump relay.
An inconsistent power supply to the pump can also come from a bad fuel pump relay. If voltage changes because of corroded relay contacts or sloppy wiring, for instance, the pump may not run at maximum output, thus keeping it from pressure up to specification. A mere voltage drop of 1 to 2 volts can quickly decrease (or starve) the fuel pump, causing long cranks and difficult starts.
In a few high-profile incidents, faulty fuel pump relays have also prompted some manufacturers to recall hundreds of thousands of vehicles. For example, in 2019, Nissan issued a recall for thousands of vehicles for faulty fuel pump relays that led to difficult starts and even engine shut-offs - showing how important the relay is to the operation of the fuel system.
Another problem related to an unreliable power supply is the reduced lifespan of the fuel pump, because the ineffective relay forces it to work harder than required. This can take 20% off the life of the fuel pump, making repairs/replacements more frequent. In this case, technicians recommend fuel pump relay testing with a multimeter to confirm continuity through the relay due to proper voltage and replacement of a malfunctioning relay being far cheaper than replacing an entire fuel pump.
To end, a quote from automotive pioneer Henry Ford: “Quality means doing it right when no one is looking”. Something as minor as a fuel pump relay can greatly affect the way the car starts, and solving these problems in advance will be crucial to having a well-running vehicle or one that may not even work!
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