Hi k-world, sad day for my 86' k100 lt (2v)... we lost power while riding and she will not restart. Managed to get back to my garage found CF et tal awesome tutorials very helpful to narrow down the issue to the fuel pump and/or connection.

So the pump is working, bench tested and it squirts. However I cannot energize the pump through fuse #6, so I suspected the fuel pump to harness connector. Decided to replace it, removed the connector and energized pump direct through the brown and blue/yellow wires... nothing pump does not turn still.

Next I removed the petrol gauge from the tank and discovered the black wire to ground terminal on the gauge is oxidized and crusty. Would that be enough to kill it??

I'm thinking short in the tank or in the external wires connecting to the fuel gauge... my next idea is to energize the pump by powering from the connections on the gauge. Is there a better way to diagnose shorts that area? Anything else I should consider?? happy trails, k

kstar wrote:
Next I removed the petrol gauge from the tank and discovered the black wire to ground terminal on the gauge is oxidized and crusty. Would that be enough to kill it??

Oxidation can inhibit function of any electrical connection. How about posting a photo of your situation?

What is the condition of the earths under the fuel tank? They are bolted on to the central spine.

Laitch wrote:

kstar wrote:
Next I removed the petrol gauge from the tank and discovered the black wire to ground terminal on the gauge is oxidized and crusty. Would that be enough to kill it??

Oxidation can inhibit function of any electrical connection. How about posting a photo of your situation?

It is a new day! With fresh hope I conducted my experiment to isolate the short bypassing the suspected connection, low and behold, the pump energized!! For my own knowledge, is there a smarter way to have found this out? I am open to suggestions on other diagnosis if you think I should consider other diagnosis for no power to the fuel pump.

My conclusion is to replace the petrol gauge unit with the wire and connections... motobins has one for about $150 usd, yikes, better than OEM prices though. Secondary action I also want to check the HES, but had trouble finding the correct 12v LED to make my own...

For all with an interest up to this point I've completed the following:

1) cleaned and made bare metal connections on all grounds. Used deoxit products liberally.
2) a few weeks ago when the bike could run I hot gun tested Hall Sensor to about 400F, no change in running. No start issue began some time after.
3) checked power to FI relay pins and FI per forum members instructions helpful link https://www.k100-forum.com/t1686-fuel-pump-not-powering-up
4) tested #6 fuse, fuse OK, but could not energize pump through it.
5) bench tested fuel pump, runs with power direct to it.
6) removed pump, gauge and energized through various points to isolate short... photo 1
7) cleaned oxidized areas and will try to improve the ground point in photo 2 and 3... slim chance that may work.








Have a great weekend!! Safe riding out there!

kstar wrote:
For my own knowledge, is there a smarter way to have found this out?

Your test method was orderly; you didn't get distracted. The smartest approach is not to assume the system is fixed until it assembled and working repeatedly, and not to assume chances are slim if your experience with a part or system is limited.

A quiet evening scouring the fuel sender and its connections with Rammstein blaring through your earbuds and the family dog—iguana, python or possum—lying adoringly at your feet might save you some money as long as the cost of your labor is reasonable. Give yourself a discount.

Thanks for the photos.

I'm wondering about a statement in your first post:

Decided to replace it, removed the connector and energized pump direct through the brown and blue/yellow wires... nothing pump does not turn still.

So there is no blue/yellow wire on a standard K-bike. So, where did this wire come from? I don't see it in the pictures you posted either.

That being as it may, your diagnostic process seems sound. The soldered connections on the passthru connector and on the ground tab of the fuel level sender look very good. In fact, the sender looks in fine serviceable condition. The surface corrosion you see on the sender has no effect on the operation of the pump. It may possibly interfere with the correct fuel level sensing but you do use that feature of the tank.

So, is there reliable continuity on all the wires in the tank lead? Can you check by probing between the end of a given wire (say the Green/White pump power wire) and its corresponding pin to see if there is no broken wires? Maybe give the wire a wiggle and tug to make sure the problem is not an intermittent break.

The only wires that matter for getting the pump working are the Brown and Green/White wires, so concentrate on them. Your problem might be intermittent or lost contact inside the gas tight passthrough. If that is the case, then the only remedy is to purchase a new sender. But if not, you might be able to workout and repair the problem with your old sender.