Underhood: Timing The BMW N53 And N54
Make sure the springs and guide rods are not damaged when the new unit is lowered into the tank. Sponsored by Carter.
On this fuel pump assembly module, the bottom part of the unit that contains the pump and pick up is held against the bottom of the tank using these rods and springs. Why?
The answer is plastic tanks. On older vehicles with steel tanks, the fuel pump was a hanger style with a pick up pressed against the bottom of the tank.
Due to the rigidity of the tank, the tank does not change shape as the fuel quantity or internal pressure changes. With a plastic tank, it can change shape under certain conditions. Remember, gasoline weighs 6.3 pounds per gallon. So a full tank can weigh as much as 130 lbs.
The fuel tank could see pressures as high as 15 psi and low as -5 psi. This can change the height of the bottom of the fuel tank.
This is why some fuel pump modules have these rods and springs to push the bottom of the tanks. Without them, the pick-up could become uncovered, and the fuel pressure could drop. Also, the sender could give inaccurate readings. Can they fail? Yes, the most common failure mode is when the plastic housing the rods and springs cracks and can’t move freely, or there is no tension.
When installing this type of pump, make sure the springs and guide rods are not damaged when the new unit is lowered into the tank.
This video is sponsored by Carter Fuel Systems.