Fuel Pump Relay dying.

[Multiplicity]

Originally Posted by roger 04 rt

I can say with certainty that the fuel pump stays running, and that the Motronic sets the injector times to zero during OFC.

Your explanation of a voltage drop during OFC is interesting, certainly a possibility. During OFC, the engine is stalled! It is firing the spark plugs, but not injecting any fuel. So more than semantically, its not running, just being pushed by the rear wheel.

If you were in OFC, say decelerating from 5000 RPM, and at 2500 RPM pulled in the clutch, the engine has to catch with very little rotating inertia--only what is has from its own mass, the rear wheel isn't driving it. I'll have to try that today when I'm out riding.

It would be nice to know at what RPM it actually dies at. That would help paint a better picture

[roger 04 rt]

Originally Posted by Multiplicity

It would be nice to know at what RPM it actually dies at. That would help paint a better picture

That's true. Since under Ofc the engine is off till 1800 RPMs, did it come back on and stall or never restart?

[Scapadu]

Originally Posted by Multiplicity

I don't how your bike is wired, but if the relay is bad it could also be a physical relation to it loosing it's
ability to control output to the pump on decel. Inertia might be why it only happens on decel. All decel fuel control is done through the injection system, not by turning off the pump. I've had relays flake out with minor voltage changes. I even had one that would only fail when the brakes were applied. A voltage threshold could be why yours is/was acting the way it did. A drop in system voltage when the RPM's drop, coupled with the load from the brake lamp could be all it takes. You removed the suspected relay and installed a known working one and the problem has stopped. Could be you disturbed a faulty connection too. To many variables to know why without failure duplication while monitoring input/output signals

I will probably subcribe to that possibility and i will tell you why.
Several time the engine cut did happened, and i should say the more often time it happened, i was having the heated grips on. Matter of fact, as i noticed that, i did wonder what kind of relationship there could be between the engine cut (and fuel pump relay) and the heated grips and thought this was just co'incidences.
FYI my batterie is relatively new and in very good shape (motorbike sleeping in a warm garage).
But now with your explaination it could have happened that due to a bad relay connection and the heated grips on, the relay released itself because of a too low voltage during deceleration.
Now, because i have worked on the relay (swapped) it is possible that the loose connection has wanished and i can no more reproduce that failure again.
To tell the truth this is the best scenario i have seen for now on that failure and i really like it. All facts are matching together, deceleration, OFC, fuel pump relay released, heated grips on, engine cut.
BTW, the iddle speed of my engine is low, only 1000rpm, it works perfect but may be i will raise it a bit to 1100rpm. I mentionned that because it happenned once, that i had an engine cut while engine was at very low rpm, but with heated grips on .

Thanks a lot guys for your experiences , which i think, put me on the good track for getting the clue (knock the wood ) .

[Scapadu]

Originally Posted by roger 04 rt

That's true. Since under Ofc the engine is off till 1800 RPMs, did it come back on and stall or never restart?

For what i am concerned, i fact it was not a true full engine cut in most cases but the fact that when reaccelerating after decceleration and with rpm between 2500 and 3000 the OFC did not stop and engine did not restart at once but after 2 to 3 secs. However it finally always restarted while it still was above 1800rpm.
The only case where the engine completly died, i was not really more on deceleration but at very low RPM, most probably below 2000rpm.

[roger 04 rt]

Originally Posted by Scapadu

I will probably subcribe to that possibility and i will tell you why.
Several time the engine cut did happened, and i should say the more often time it happened, i was having the heated grips on. Matter of fact, as i noticed that, i did wonder what kind of relationship there could be between the engine cut (and fuel pump relay) and the heated grips and thought this was just co'incidences.
FYI my batterie is relatively new and in very good shape (motorbike sleeping in a warm garage).
But now with your explaination it could have happened that due to a bad relay connection and the heated grips on, the relay released itself because of a too low voltage during deceleration.
Now, because i have worked on the relay (swapped) it is possible that the loose connection has wanished and i can no more reproduce that failure again.

...

You've got an interesting intermittent problem.

While decelerating, even in OFC, the engine RPMs are high (above 1800) so your alternator should still be putting out full power.

I doubt it is your problem but BMW changed the panel warning light for the Alternator from 1.7W to 3W. The reason I mention this is because at low RPMs and just after starting, it is this Batt/Alt warning light that provides the field current to the Alternator to start running. On my 1150 I noticed that after starting the Batt/Alt light wouldn't go out until I blipped the throttle and increased the RPMs. That left the voltage low after starting, which led to the injectors putting out about 10% less fuel at cold idle until the Batt/Alt light went out.

In my case the Hi Beam bulb was 3W, the Batt/Alt was 1.7W so I just swapped them, problem solved.

[Scapadu]

Have done over 600km since i swapped the fuel pump relay, the engine cut no more happened. Looks to be fixed now.