K1100RS intermittent starting

[Bunny]

Hi all - new to the forum so firstly Hello from the UK




Have a 93 K1100RS which had been stood for 10 years
Completed a service - new plugs, oil, filter, fuel filter, fuel !!, fitted new tyres and suspension - ran beautifully
Done about 700 miles, bike started missing
Got her home - started fine, ran for a couple of mins then cut out
When I turn the ign off and then back on, if the fuel pump primes and then stops, the bike starts and runs - sometimes great - sometimes as if on 3 cylinders
If the pump primes but then keeps running (don't think it did that before) the bike will not start.
There is fuel returning to the tank through the pipe at the top near the cap


Is the priming time activated on a timer or by fuel pressure ?


Checked fuses , relays , connector to fuel pump from loom


thanks for any help


Bunny

[Laitch]

Welcome! Post some photos of the offender.  :yes How many miles are on the odometer?

When the bike is in neutral, on the center stand and the side stand is up, will it start?

[Bunny]

Bike has done 36800 miles

All the above was done with the bike on the centre stand in neutral with the side stand up
If I put the side stand down the fuel pump will not work at all

Will post some pics when I work out how :-)

[Scott_]

When the key is turned on, the pump prime time is controlled by the Motronic. If the pump is staying on, and you can turn it off without pulling the fuse, it's looking like an issue with the HES sensor inputs(telling the motronic to turn on/keep on the fuel pump) or an issue with the Motronic itself, or the ground wire from the relay to the Motronic.

So when the pump is staying on and not starting, how are you stopping it-- Key switch, Kill switch, Fuse?
Have you DeOxit cleaned the Motronic connection.
Have you checked for any fault codes.

[Bunny]

Hi Scott,


I am turning off with either the key or the kill switch


So if the priming time is controlled by the Motronic  which sensor sends a signal for it to stop priming ? I thought it was a fixed time or set pressure that stopped it


Have tried to read fault codes but diagnostic fails to connect - comes up with an open circuit failure - which may be connected to the fault or not ?

[Laitch]

. . . if the fuel pump primes and then stops, the bike starts and runs - sometimes great - sometimes . . .

When the key is turned on, the pump prime time is controlled by the Motronic. If the pump is staying on,. . .

So if the priming time is controlled by the Motronic  which sensor sends a signal for it to stop priming ?

I don't understand these statements and I've had a half liter of coffee this morning. The fuel pump shouldn't stop.

I thought the only signal the pump received was in the form of current to start it or to stop—not to prime or not prime. Priming is the act of the pump's restoring fuel pressure after the bike has been shut down and fuel pressure has lessened. It does this by running up to full speed as it intakes fuel and fuel pressurizes the lines. That takes a few seconds. What should follow is ignition and the pump will just continue running at full speed to keep the system pressurized for management by the fuel pressure regulator. It's like any other one-speed sump pump. It has a different pitch note, or sound, when the system is pressurized. Usually it's quieter after pressurization. When the pressure is up, it just keeps on running. It plays a one-note samba right up until shut down for dismount and sack time.

Will some clarify for me this idea of the pump's stopping as a normal circumstance while the bike is running? I still have more coffee.





 

[Scott_]

The motronic activates the pump for a short 2-3 seconds to pressurize the fuel rail. It then stops the pump until it sees signal from the HES sensors that the engine is turning. It will continue to energize the pump as long as it sees signal that the engine is turning.

Sent from my SCH-R970 using Tapatalk

[Bunny]

So, is the sensor that tells the motronic the engine is spinning a crank sensor ?
There is no continuous fault - sometimes the fuel pump "primes" for 2 secs, then drops out until I hit the start button at which point the pump restarts, other times the fuel pump is continuously on with the ignition - regardless of whether the engine is turning or not.
Also it only fires up sometimes now, even if the pump stops before I press start.
It was starting every time the pump "primed"- even if it only ran for a while.
Is there a manual/wiring diagram for a pre 94 bike available ?
thanks

[Scott_]

So, is the sensor that tells the motronic the engine is spinning a crank sensor ?
There is no continuous fault - sometimes the fuel pump "primes" for 2 secs, then drops out until I hit the start button at which point the pump restarts, other times the fuel pump is continuously on with the ignition - regardless of whether the engine is turning or not.
Also it only fires up sometimes now, even if the pump stops before I press start.
It was starting every time the pump "primed"- even if it only ran for a while.
Is there a manual/wiring diagram for a pre 94 bike available ?
thanks

yes, it is a crank sensor. It's at the front of the motor behind the "T" shaped cover.

Sent from my SCH-R970 using Tapatalk

[Laitch]

The motronic activates the pump for a short 2-3 seconds to pressurize the fuel rail. It then stops the pump until it sees signal from the HES sensors that the engine is turning. It will continue to energize the pump as long as it sees signal that the engine is turning.

Thanks, Scott_. Your explanation identifies the primary and secondary signal for fuel pump operation and increases my general understanding.The K1100 pump in this case should only operate for a few seconds after the ignition-on key switch position unless the engine is being cranked or running, then it continues running full speed. In the K75, the pump starts running when the starter button is pushed. Both bikes depend upon Hall Effect sensor signals to continue fuel pump operation.

Cleaning the Motronic plug would be my choice of direction now. It's a simple plan.

Is there a manual/wiring diagram for a pre 94 bike available ?

Look in the Repair Guidance section's Master List. There is one in the Electrical Wiring Diagrams section.