1993 BMW K75S - fuel pump not running when starter button pushed. PROBLEM SOLVED

[gibohobo]

Please help.  I have 0.09 volts on the fuel pump when I hit the starter button.  The pump runs when power is jumped to the #6 fuse.  I have tried cleaning the starter brushes.  I have also purchased and installed a new sending unit.  I  still can't figure out where the voltage drop is occurring.  I have 10 volts to the plug pin before going into the sending unit.  I have checked continuity on all of the pins to the sending unit and everything is good.  I am perplexed.  I would appreciate any help I can get with this issue.  I am a long time lurker on the site, first time poster.

[Laitch]

I am a long time lurker on the site, first time poster.
I have 10 volts to the plug pin before going into the sending unit. 

It looks like you're a 10th-time poster. 

On which side of the 4-pin connector—the pump side or the relay side—are you getting a 10V reading?

[gibohobo]

relay . I am getting the .09 on yellow wire on pump

[Laitch]

relay . I am getting the .09 on yellow wire on pump

Your connector's pump-side component could be faulty. Cleaning the receptor thoroughly with a emery cloth and DeoxIT contact cleaner might restore the full connection, if that's the problem. Consider replacing both sides with a new waterproof connector like this one; however, there are many aftermarket connectors from which to choose.

[gibohobo]

I just ordered a new conneector. But still wonder why when I jump power to the sixth fuse the pump runs

[Laitch]

I just ordered a new conneector. But still wonder why when I jump power to the sixth fuse the pump runs

Describe exactly the points being jumped.

[gibohobo]

straight jumper wire from positive of battery to sixth fuse down . I got that from somewhere else on Motobrick for testing pumps.By the way I hardwired from sending unit to harness and it still reacts the same

[Laitch]

By the way I hardwired from sending unit to harness and it still reacts the same

What is the it—the multimeter reading of 0.09 or the pump's running ok?

[gibohobo]

When I jump straight from battery to sixth fuse the pump runs. When all proper connections are made I only get .09 at pump and it of course does not run. When I disconnect the connection at tank, I get 9 to 10 volts on the connection pin. I'm unsure how I get voltage drop when pump is under load.

[Scott_]

When I jump straight from battery to sixth fuse the pump runs. When all proper connections are made I only get .09 at pump and it of course does not run. When I disconnect the connection at tank, I get 9 to 10 volts on the connection pin. I'm unsure how I get voltage drop when pump is under load.

Voltage drop under load is usually caused by a weak/bad/dirty connection. It is good enough to allow voltage potential with no load, but is not good enough to pass current under a load.

[gibohobo]

It was FI relay,I did not think of changing it out sooner because I had voltage to sending unit.I Switched it  out with load shed relay and pump now runs.Both relays are the same and with the relay that was previously in fi now in load shed the turn signals do not work.Just ordered new one from Euro MotoElectrics.

[Laitch]

It was FI relay . . .

Good work. Thanks for the followup. 

[volador]

Amazon Lime Relay



FI relay 5blade 61368373700

Load shed 4blade 61311459677   Relay, K75 - K1100LT; R80R - R100MYS. This relay is assigned to multiple uses. Including: fan, starting load shed, horn, Motronic, and fuel pump on selective models.