electrical problem fuel pump -90 K75RT

The K was running when parked 5 years ago in a dry garage. not set up for long term storage. installed a new fuel pump kit w/hoses & screens. pump doesn't seem to be getting power, will not prime lines. normally you can hear the pump building pressure when you 1st turn the key on. that is why I replaced the pump to begin with. the bike will run/sputter if you spray some starting fluid in the air filter. where else can I look for an electrical problem on the fuel pump. fuse is good (not blowing fuses) thanks

madmatt said:

The K was running when parked 5 years ago in a dry garage. not set up for long term storage. installed a new fuel pump kit w/hoses & screens. pump doesn't seem to be getting power, will not prime lines. normally you can hear the pump building pressure when you 1st turn the key on. that is why I replaced the pump to begin with. the bike will run/sputter if you spray some starting fluid in the air filter. where else can I look for an electrical problem on the fuel pump. fuse is good (not blowing fuses) thanks

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On a K75 the pump does not come on when the key is turned on. It is activated for a few seconds when the starter button is pushed, and is then kept on when the ECU is signaled from the Hall Effect (crankshaft position) sensor.

To make the pump run just stab and release the starter button. If it doesn't come on check the fuses. Fuse 6 I think but am not sure.

If the inside of the tank deteriorated badly while the bike was idle, you may need to replace the sensor assembly, since that is what conducts power from the external connector to the internal pump wiring. I have seen corrosion on it that kept power from getting to the pump.

Overall, though, you need to follow the voltage remembering that the pump only runs when the engine is turning. Power at the connector plug? If so, power at the wires on the pump? If not, power at the fuse? And so forth. The tank connectors are notoriously flaky.

I went through this. There are two places the fuel pump commonly loses power on K Bikes. The four pin connector under the tank, and the plastic pass-through that holds the float assembly.

Start with the four pin connector since it is most likely. Clean the contacts and make sure they connect well. The female side tends to open up, so just gently close the slot with a small screw driver. Plug it in and see if it starts.

If not, check the continuity between the tank side of the connector and the fuel pump with an ohm meter. The pump wires should connect to two of the terminals on the connector. If not, the pass through is open and needs replaced. BE CAREFUL, the tank is full of gasoline vapors!

If they are good, then check the pump wires on the connector (bike side) are getting 12V when you hit the starter.

Sorry, I do not remember the wire colors off hand.

Good luck,
Scott

https://forums.bmwmoa.org/showthread.php?72833-Fuel-Tank-Pump-Level-Sensor-Wiring-All-Early-Kbikes

These old K bikes don't store well unless prepared for storage.
That being said, I bought a 1990 K75rt about 2 years ago. Ran great for about 50 miles then quit and would not re-start. Towed it home and parked it in te garage. The next morning started as if nothing was wrong. Replaced the fuel pump and filter. Made it 30 miles on the next ride. Went through te bike cleaned every electrical conector I could find, still no joy. Checked the fuel sender (float) in the tank and found it would short out when the engine got hot. Replaced the sender and no issues in the last 500 miles. The Sender is the weak point in the system. It's also expensive about $200.00 from EME.

CNRed said:

These old K bikes don't store well unless prepared for storage.
That being said, I bought a 1990 K75rt about 2 years ago. Ran great for about 50 miles then quit and would not re-start. Towed it home and parked it in te garage. The next morning started as if nothing was wrong. Replaced the fuel pump and filter. Made it 30 miles on the next ride. Went through te bike cleaned every electrical conector I could find, still no joy. Checked the fuel sender (float) in the tank and found it would short out when the engine got hot. Replaced the sender and no issues in the last 500 miles. The Sender is the weak point in the system. It's also expensive about $200.00 from EME.

Click to expand...

EME ??

madmatt said:

EME ??

Click to expand...

http://www.euromotoelectrics.com/Default.asp

So after a month, have you determined that the pump is getting that couple seconds of power when you first push and release the start button?

Did you get the polarity right on the pump?

Without further info, odds are your injectors are plugged. We need more info.

The sender assembly does not usually fail during storage. I would not recommend throwing parts at it. Do some basic troubleshooting to find the problem. We can help with that.

Finally got around to looking at the K75

Not being much of a mechanic I was quite apprehensive about tackling the repair. After removing the float gauge found one of the wires passing thru the bottom of the tank had rusted off. It WAS one of the wires going to the fuel pump. Installed a new "fuel float level gauge" (a new gasket comes with the assembly so don't order one separate like I did). When I got the K some of the fuel lines inside had dry rotted and broke apart, I wasn't sure what line went where, uTube helped there. Still won't start. fuel pump is working. I'm thinking the pump lines have a leak in the tank. I can see fuel swirling in the tank so it must be a leak and can't pressurize. put in new spark plugs (broke 3 plugs trying to tighten in cyl #1, the porcelain). pretty frustrated, I'll get back to it in a couple days. Daughter's coming in from the West coast to visit.

Good thing I have a K12GT also.

Fuel swirling in the tank is not necessarily a sign of something wrong. The return from the fuel pressure regulator will cause that.

Is the arrow on the fuel filter pointing away from the pump? Is the filter new?