What does the TPS actually do?

[Red ones]

As per the title.

[tom_e]

It tells the engine the position of your throttle.

https://en.wikipedia.org/wiki/Throttle_position_sensor

[Eulaca]

Within the ECU is a table of timings for the fuel injectors. Along one axis of the table is throttle position, along the other axis is rpm. So when your engine is at 3000 and the throttle sensor is at 40% the ECU knows to spray the injectors for X seconds for every timing signal it receives.

The above is an over simplification as other sensors modify what's on the table (air or engine temp for example).

[Red ones]

I had deduced with my Sherlock like skills that the Throttle Position Sensor actually just senses the position of the throttle. But why does that matter?

And furthermore why do they set at the factory that it changes at 3,500 RPM?

[yorkie_chris]

The sensor is proportional.... depends how many bits but probably something like 0-100% throttle is 0-5V divided into 1024 values.

The block that moves up at 3500rpm is just an indicator not an actual step-change in value.


Because you've got this satans sneeze setup of fuel injection rather than a proper set of carbs... the ECU needs to know how much air the engine is getting so as to squirt the right amount of fuel.

When TPS is moving the block at 3500rpm this means your initial throttle take up is going to be a bit lean... moving the TPS "signal" down to 1200rpm or similar gets it back in line... the ECU "sees" the right amount of beans being given, and delivers enough fuel early enough in throttle travel to smooth things out.

[Sid Squid]

It isn't set to 3500rpm at the factory. See my posts on the subject as to why this isn't so.

TPS function:
The simple answer is true: the TPS is a device that tells the FI/Ignition system the position of the throttle. This makes no decisions on behalf of the system, it merely informs of whether you want less, the same or more power than presently. When the FI/Ignition system is informed of what you want, it makes decisions on fueling and ignition settings based on that, and the information from other sensors; temperatures, pressures, speeds and positions, with reference either to a multi axis map, or, in certain circumstances, according to further sensor/s such that some settings can be made in real time rather than empirically.
One important throttle position is shut, there are settings in the system that ensure smooth, reliable idle, and least emissions when you don't want any power, such as at coastdown.

[Red ones]

On that basis, why the jerkiness we all remove by adjusting the TPS? Is the mapping just carp?

[Sid Squid]

It's not a particularly sophisticated system it's true, but no, it's not crap, far from it.
As mentioned above, an important throttle position is shut, and the settings that give a nice smooth, reliable idle and emissions friendly coasting are not really suitable for running otherwise, but the problem is not that exactly, it would drive perfectly smoothly (if not to best effect) on those settings if they didn't alter, but the jerkiness is felt as the transition between the two happens. When set correctly the throttle position is indexed to transition immediately the throttle is cracked, if it's set wrong (and wear will always cause the TPS to lag) the transition won't occur until you've got some revs in and the clutch out, hence the lack of smoothness.

Originally Posted by Red ones

I had deduced with my Sherlock like skills that the Throttle Position Sensor actually just senses the position of the throttle. But why does that matter?

And furthermore why do they set at the factory that it changes at 3,500 RPM?

It matters 'cos it tells the bike whether you wanna go faster or slower innit!






Ignore me, I have no knowledge to add unlike these fine people, I'm just yanking your chain!