I'm trying to diagnose an issue with plugged fuel filter and/or air leak into my fuel system. I know that the lift pump operates when the key is turned to glow plug position. Once the motor starts, does the lift pump continue to operate, or does suction from the high pressure injector pumps pull the fuel in without a lift pump? (Neither owners manual nor service manual is 100% clear on this, though there's a slight hint in the troubleshooting that the former is the case.) If it's actually the latter, does anyone know for sure whether the secondary pump is under negative pressure or positive pressure?
In a related question/comment, if the lift pump continues to operate when the motor is running, I assume that the excess fuel continuously recirculates back to the fuel tank, continuously polishing the fuel. Is that correct based on your understanding? (Note that this is an M35BC model.)
In a related question/comment, if the lift pump continues to operate when the motor is running, I assume that the excess fuel continuously recirculates back to the fuel tank, continuously polishing the fuel. Is that correct based on your understanding? (Note that this is an M35BC model.)