“TPS” stands for “Throttle Position Sensor”.
With fuel injection, it is the part that tells the computer how far the throttle is open. When the throttle is closed, the TPS sends a certain amount of voltage, say .60 volts, to the computer, also known as the “ECU” or “Electronic Control Unit”.
The ECU already knows that when the TPS is putting out .60 volts, that the throttle is closed, or at zero percent open. It knows the bike is just getting enough air to start and idle and the ECU is pre-programmed to give the engine enough fuel for it to idle.
When the throttle is wide open, the ECU sees the throttle at 100% open. At 100%, on the 2012-16 EXC, the TPS is putting out a voltage of around 3.74 volts or a bit higher.
Basically, as the TPS's voltage output increases, the ECU thinks that the throttle is open further and gives the bike more fuel, to keep up with the extra air flowing past the butterfly or throttle plate.
The TPS is the main input to the ECU, other than the RPM pick up, to get the engine the right amount of fuel.
The TPS itself is adjustable (can be moved forward or back) on the 2012-16 EXC's and XCW's. This means that when you twist the TPS against the way the throttle opens, the voltage output is a bit higher at every throttle opening than it really should be. The ECU only see's the voltage number.
It gives the engine a little more fuel now than it gave it before, even though the amount of air is still the same. This is how you fool the ECU into providing the engine more fuel, with TPS turning, or "TPS Tuning", as it's known.
This is our TPS tuning tool below. It's a voltage source that puts exactly 5.00 volts into the TPS. This is how the factory sets the TPS, by putting 5.00 volts into it and then setting it's output voltage.
All the numbers of TPS voltage in your service manual are based on exactly 5.00 volts going into the TPS. If more voltage goes into the TPS, then the output number is higher. If less, then it's lower.
With fluctuating input voltage, you can never really correctly set or tune your TPS for desired performance.
Trying to tune your TPS by any other means then using a perfect 5.oo volt source, like this, with your bike NOT RUNNING, is the only correct way to evaluate the difference that increasing or decreasing your TPS output voltage has on your bike.
It's like trying a different tire every ride but with a different air pressure every time. You have too many things changing to really know what's better.
This is our TPS tool putting out exactly 5.00 volts.
By placing the little jumper wire between the red and yellow wire and turning the adjustment screw on the side, you can raise or lower the voltage coming out of the box, until you get to exactly 5.00 volts.
These tools come pre set so you don't need to worry about setting the output voltage too often.
This is your throttle position sensor here on the side of the throttle body below. It's under the rubber cover on the shifter side.
You can get to it with the tank on so you can loosen the screw holding it down, plug the tool in and change the output voltage on the side of the trail. Then tighten the screw down, disconnect the tool, plug your TPS clip back in and ride again.
An easy way to see if you like it better or worse.
The manual calls for the TPS on 2012-16's to be set at .58-.60. Many come at .57. Even if you do nothing else to your bike, setting the TPS at .60 makes a big improvement in ease of starting, idling and low end response and power.
You can turn a TPS up to about .78 or so for output voltage. Replace the exhaust tip with a BDSB cap and play around with the settings. You'll be surprised at the difference.
TPS tuning with a stock EXC or XCW fuel map in your ECU works better for performance and mileage than if you were to use a European map in your ECU.
Even if you do have a Euro map, the bike will still run better with the TPS fine tuned, so it's a valuable tool regardless.
After adjusting the TPS output, you may have to re-adjust your idle speed.
This round black knob here, on the upper, shifter side of the throttle body, is the knob that controls the idle speed.
If you turn it clockwise the idle will lower and if you turn counter-clockwise it will raise. Be sure the knob is pushed in when adjusting or the bike will just idle real high.
If you’re ready to get our TPS Tuner for your bike, you can do so below for only $99.95.