Fuel pump no power

[fastxl]

After replacing fuel pump, plugs, refurb fuel injectors and a bunch of other stuff bike ran great for about 100 miles. Started it Friday morning let it warm up, shut it off, came back a few minutes later and no start. No Fuel Pump sound. Drained the fuel today, check voltage at the fuel pump and got no reading. Pulled the connector that connects the fuel tank and check voltage but putting one lead on the brown wire and one on the green/white wire and I get voltage when I hit the start button. Is this telling me there's something wrong with the fuel level thing in the tank?

[Laitch]

. . . came back a few minutes later and no start.. . .Drained the fuel today, check voltage at the fuel pump and got no reading.

Cranked but wouldn't start, or wouldn't even crank? There's only voltage at the fuel pump when the engine is cranking.

[fastxl]

Cranks over just fine, will even sputter but since the fuel pump won't come on it will not start running. No voltage at the fuel pump while cranking. From what I am reading, I suspect the fuel level sending unit.

[daveson]

Could be the four pin connections are loose, it's often the fore pin. Maybe the pump will run with a battery connected to the other half of the fore pin.

[frankenduck]

Not uncommon for the fuel tank connector to fail internally on Ks.

You can use ring terminal connectors to jump 12V power directly to the fuel pump in order to diagnose if that is the  problem.

The smaller diameter terminal with the yellow wire going to it is 12V+.

[The Mighty Gryphon]

The connector for the fuel tank is a common problem area.  That you see power on the harness side of the connection but the pump is not running tells us that your connector is not making good contact. 

I would suggest that you check continuity from the pins on the connector to the fuel pump.  If there is good continuity the problem is in the connection between the male and female connectors. 

There are several approaches to correcting the problem.  First is to give it a shot of Deoxit and work them in and out a few times to clean up any corrosion that may be present.  Second is to distort the pins and the sockets to help make better contact.  The third and most extreme is to replace the connector.  This last approach usually yields the best long term results.

[fastxl]

I am going to say it is something with the fuel level unit. I check continuity (I think) and I get this reading on the green pin to the + side of the fuel pump.


BMW-1.jpeg (105.43 kB . 768x576 - viewed 372 times)

While the Yellow and Brown show this.


BMW-2.jpeg (63.5 kB . 432x576 - viewed 368 times)

[daveson]

You haven't got good continuity for power, could be the plug, level sensor, pump or wiring. If the pump runs with a battery to it, that's OK. If you push the probe through the insulation just behind the fore pin plug green/white wire and the continuity is good, then it's the four pin. The pin might be loose from the wire. Sometimes the wires to the pump are brittle, the wire could be broken along its length and feel soft and weak there.

Use the probe at a few points to isolate where the problem is (for example, is the continuity good from both ends of the yellow wire)

[rbm]

White and Yellow wires have nothing to do with the pump.  They are related to the level sender, which is a completely isolated circuit.  Concentrate on Green and Brown.

[daveson]

Maybe I should have said the positive wire in the tank from the pump to the level sensor which is shown as yellow in the wiring diagram I was looking at.

[frankenduck]

White and Yellow wires have nothing to do with the pump.  They are related to the level sender, which is a completely isolated circuit.  Concentrate on Green and Brown.

The green and white 12V wire becomes a yellow wire once it enters that tank.

[fastxl]

The green wire from the plug to the level sender seems to be the problem. The yellow wire from the sender to the fuel pump is good from what I can tell. Anyway to replace the wire going from the plug to the sender? Looks sealed with some sort of epoxy.

[fastxl]

So I caved in and bought a new level sender from Euromotoelectrics. Installed and fires right up and runs well. However the low fuel light is on and I have plenty of fuel in it. Even moving the level arm up and down in the tank with a coat hanger doesn't shut the light off. Looks like I have to trouble shoot this now.

[rbm]

Should be easy.  Low fuel is a wiper on the sender that contacts  copper pad when the fuel is low.  It sends a ground signal to the cluster that turns on the light.  Pull the tank plug and use an ohmmeter to test White and Brown pins on the sender side of the connector.  If there is no continuity (which there should not be if your tank is filled beyond the low fuel threshold), then the sender is ok - you might have a ground short in the harness or the cluster.   If you show continuity with the above test, the sender is not working properly.  You'll have to remove it an troubleshoot what's going on. See my writeup "Messing with the In-tank Fuel Sender"

[Laitch]

See my writeup "Messing with the In-tank Fuel Sender"

But don't spend time searching for it here. It's more easily found at this link. Possibly it's just out of adjustment and following instructions with the link will get it working.