No start...looks like no power to fuel pump?

[canada karl]

I suspected bad wiring or a bad fuel pump so I replaced the pump. Put 10 litres of fuel in the tank. Put a hose from the pump outlet to a jar to see if the pump was pumping fuel or if I had the unmarked wiring reversed. Turned the key,starter cranking ...no fuel coming out of the pump? Changed out the fuel pump relay with two different spares. No change? How do I proceed from here? Odd thing is when I turned the key on the fuel gauge would register 1/4 tank. Now when I turn the key on the gauge needle dosn't move? Any ideas most appreciated.

[528i-1981]

Karl - I learned from Lock that "there are no coincidences" but in this case, if it were me, I'd ignore the gas gauge symptom initially and focus on the pump. I think that trying to find a common cause for both faults brings you back to the ignition switch, and first you should find out if the fuel pump wiring is faulty. Did you verify that the replacement pump works? I would disconnect it from the harness and connect it directly to 12V and verify is turns. Note that these pumps are cooled by the gasoline flowing through them so don't let it turn for long, just make sure it's alive. If it is alive then I would wire it into the car and first inspect where the aftermarket black wires are tied into the factory harness and ensure the connections are good.

The main pump and the in-tank lifting pump are energized by the same wire (Grey/violet). The inlet hose to the main pump should receive at least some fuel when the circuit is energized by the lifting pump, if it's in working order. But with only 1/4 tank and because the in-tank pump gets feeble with age, maybe not. But you can hear it easier if you pull the trunk carpet out and remove the round covering plate.

Next I would test if the pumps activate by depressing the AFM flap with the ignition ON. You'll need to remove the airbox or the bellows between the airbox and the AFM. If this fails then I would jumper the combo relay terminal block to turn on the fuel pumps. I don't know which terminals off the top of my head and I'm away from my sources. You can find the answer online if nobody chimes in.

If neither of these activate the pumps (you should be able to hear it turning if the ^%!@#$%^ key warning buzzer is off), then
i think at this point you'll need to trace the wiring, including the ignition switch. If either works then you'll be able to narrow the issues knowing the wiring is good.

These are just what comes to mind, certainly not exhaustive and others may have some suggestions.

Good luck and let us know how it works out.

[528i-1981]

As Robert Bondi pointed out on another thread, the '77 did not have an in-tank lifting pump. This correction posted for posterity.

[canada karl]

Well the issue was that I had the fuel pump wires hooked up the wrong way around so I could hear the pump when I opened the AFM door but that was why I was was not getting fuel. Also the 3 wire connections at the top of the tank(for the fuel gauge) were rust corroded and one was broken off! I removed the fuel tank assembly metal sending unit from the 76 parts car. In 77 BMW switched to a side filler gas tank instead of the earlier rear type. They also changed the top plate of the sending unit. The 76 sending unit top is a spin on type with a rubber O ring as a sealer. The 77 is held down by 6 small bolts and has a rubber gasket. Well I needed to put the the 76 unit into the 77 . There was a bit of a gap when I dropped the unit in so I used both O ring and rubber gasket to take up the gap. Since the 76 unit did not have the 6 holes for the bolts(I wasn't about to drill holes in the gas tank) I determined that because of the indent in the the 8" cover plate it should be able to put enough pressure on the inlet and and outlet hoses to to force the sending unit down tight on to the gaskets by tightening the 3 screws. Seems to work . Going for a test drive to see if it's sealed.