What happens to the fuel pressure when the standby fuel pump is off?

When the standby fuel pump is off, the fuel pressure decreases. This is primarily due to the fact that the standby fuel pump is designed to maintain fuel pressure within the system when the main fuel pump is not operating or when additional fuel flow is required. When the standby pump is engaged, it helps to ensure that fuel is consistently supplied at the necessary pressure to the engine, which is critical for maintaining performance and efficiency.

When the standby fuel pump is turned off, the only pressure regulation comes from the main fuel system and any existing pressure within the fuel lines. However, without the additional support and pressure that the standby pump provides, there can be a drop-off in fuel pressure, especially if the engine demands increase or if there are any leaks or restrictions present in the system. Thus, the overall effect of turning off the standby fuel pump leads to a reduction in fuel pressure.