Firstfives.org

Of all the cars I remember having in my time, when the key is put to the "on" position (not the start position), the fuel pump engages and pressurizes the line.

Tell me this also holds true for an '80 528i. If youve followed any of my previous threads, Ive been trying to track down a starting problem that is fuel related. When I turn the key to the ON position, the pump does nothing, its brand new. When the car is running, I can hear it working.

When I pop off the air filter to expose the AFM flap, if the key is in the ON position and I open that flap maybe less than a 1/2 inch, I can also hear the fuel pump engage.

I only ask to clarify.

Clarification correct.

There is a miniature simple contact switch that breaks contact for energizing the fuel pump in the completely closed flap position. This was a fuel safety design engineered into the L-jet system to keep fuel from running in the system in the event of a collision, where the key would be in the 'on' position but the engine not running - the fuel system is under significant pressure, and a potentially ruptured fuelline would spew fuel virtually insuring a fire.

It is supposed to work that way. Engine off, no fuel pump operation. Two things energize the fuel pump - 1) the aforementioned flap switch and 2) the combo relay, in the key 'start' position. When the engine fires, then the flap opens, closes the switch and keeps the pump(s) energized until the key is switched off, or the engine stops running (for whatever reason).