Throttle position sensor voltage drops after engine start

Rafal · 3. September 2011

Hello!

I checked TPS voltage on my K1100. On ignition on the voltage is 3,6V - in the window. Yet after engine is started, the voltage drops to 3,2V. That is something strange to me. Can any one tell if it is normal, or TPS should be set on running engine, because vacuum change butterflies position (close them)?

Best regards,

ReneZ · 4. September 2011

Good question! Not an easy answer I guess.
IIRC when the bike starts and the 'closed throttle' signal is received there seems to be a little fuel enrichment controlled through the ECU. I wonder if that is what you measure. Off course where the TPS is connected to the ECU you don't measure only the TPS resistance, but also the connected electronics.
Alternatively, is there a way to see/measure if the throttle shaft moves? Where the iddle has been set with the bypass screws and not with the set screw I can imagin that a bit of movement would be possible.
More importantly, what doesn't work as expected that made you look at this?

Rafal · 7. September 2011

Hi ReneZ!
I had to think about the answer to your question. Well the TPS check is related to rich engine running issue. My bike runs to rich mixture it could be TPS set up or vacuum leak or injectors failure, or pressure regulator ;). I decided to start with the easiest accesses system.
I could replace TSP with some resistors to start an engine and then measure resistance to see if the TBs shafts moves under vacuum pressure.

Best regards,

ReneZ · 10. September 2011

Hi Rafal, what changed or when did you notice your bike suddenly running richer?

You could indeed look at what you listed, but alternatively could the ECU be in the 'home coming mode'? I guess we're talking about the 1100, not the 75.

Rafal · 19. September 2011

ReneZ - good point, yet I don't know how to determine if engine works in "home coming mode".
Rich running, well: the smell of gasoline after start, black smoked exhaust, a bit to big fuel consumption and CO level problem on diagnostic.
Or all above can be caused by air leak?

Best regards,
Rafal

ReneZ · 28. September 2011

Hi Rafal, I don't have a 1100, but understand that you should be able to read the ECU somehow. Maybe ask your question on K11OG forum?

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Throttle position sensor voltage drops after engine start

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