Throttle Position Sensor

There has been plenty of discussion about this device with the exception that nobody has talked about how it functions. I am going to assume that is advances or retards ignition timing? From what to what? Evidently it is not critical to operation as I believe the YZs don't have this on their carbs, additionally it seems that many have disconnected it. From what I've picked up here one way to diagnose a problem with it is to do just this.

Can anybody here shed some light on the subject.

Thanks, Ron

The throttle position sensor give's the computer feedback on how fast the throttle is opening or closing as well as the position of the throttle. There are other sensors that work in conjunction with this sensor to help the computer figure the best ignition timing and injector spray duration for the demands put on the motor.

Why do some people run with this disconnected? Don't know.

Why does the bike continue to run? This is a function of the map that the computer reads to calculate ignition timing and injector duration based on all the feedback from all the sensors. A well design system will realize that the sensor is not functioning and have an alternate map of values (via open loop) to use to calculate ignition timing and injector duration (It may also be the throttle position sensor does not have much weight when figuring the overall equation). I've worked on a number of cars and trucks with fuel injection, but never had a bike that had this type fuel system. Fuel injection is great, but still I like a simple carb for my bike. Of course, I'm still the type of guy that prefers to have a kick start on my dirt bike.

Edited by t_bois

After re-reading your post -

There is another system that uses a carb and a computer, which I hate. It was used for a short time in the auto industry. Hopefully this is not a system that is being deployed in dirt bikes as it is junk. It's like taking the worst of 2 worlds to create one!

With this system, a carb will be outfitted with a number of solenoids that get modulated with an on/off pulse generated by a computer. The computer (via the solenoids) will allow the fuel mixture to be modified by changing the open/close duty cycle of the solenoid, which will allow for a more quicker change in fuel mixture when demands require.

The reason I hate this system is that adds another point of failure with little or no gain in performance.

But to get back to your question, the throttle position sensor serves the same purpose here as what was stated about. It gives input to the computer to help determine when the mixture needs to be a bit more rich or lean by detecting how fast the throttle is being opened or closed. Some compare it's function to that of an accelerator pump.

Edited by t_bois

Only the 2010 YZ 450 is FI, all the other bikes use TPS to select the appropriate ignition map only as they are all carbs.

The reason people disconnect it is to quick test it.Disconnected, the bike reverts to a RPM based map and ignores TPS signal. In this 'limp mode' if the bike runs better, that typically confirms something is wrong with the TPS. Next step is to get a meter and the manual and go through the tests to see if it is defective or simply out of adjustment. Left disconnected, perfiormance drops off severly.

Most motorcycles have few sensors, the weight gain and increased electrical draw outweigh their benefits. Typically, the TPS, a MAP and and RPM, some do have temp sensors and that is about it. Big bikes tend to have a few more as well as lamda A/F sensors.

Interesting. So, if you removed the TPS or the MAP would it react the same way?

Is the YZ fuel system similar to port injection or thottle body?

You are mixing things up and not being clear. On a CARB'D bike (2009 and earlier YZ450, all WR450s as of right now), the TPS being disconnected is a test method for poor TPS operation. No MAPS on a FCR.

On a 2010 YZ450FI (fuel injected) , the bike will still run with the MAP unplugged (albeit real poorly), it will not run with the TPS disconnected. It will idle but that is all.

Similar to port injection though the injector is right near the butterfly, which is right next to the port.

TPS on a carb'd bike only adds data. It is not critical, it meely enables the CDI to fine tune the ignition timing. TPS is critical on a FI machine as the machine has no way to know how wide open the throttle is otherwise, it could only guess based on RPM. If the bike were idling and you opened the throttle, the bike would stall as there is not enough fuel at idle mode to enable higher RPM. Theoretically, if you could get the RPMs up, the system could guess the fuel needed, but a stall is the typical result.

You gotta love this site. Thanks for the info.

The TPS on one of my WR426s was disconnected when I purchased it and seems to run fine. I rode it 1 or 2 x a week for about a year. Should I connect it up again?

I don't really understand a whole lot about what it does. I get the basic idea ...



If... the TPS is in good condition, properly adjusted, you will get more power.

TPS is usually guilty of bike running poor/stutter at steady throttle, I run my 07'WR in supermoto trim mostly on the road and have it disconnected, runs like a dream at any revs

Then you would love the WR, because it isn't fuel injected, and it has a kickstarter if you choose to use it.

I don't believe this sensor has any ability to alter the fuel mixture. But specifically I would like to know about the sensor in this particular machine. All the rest of this is interesting, but I have read post after post after post about the surging at a constant throttle position going down the road. It's certainly tolerable, but if there is no performance gain I could do without it. I suspect what is happening is the timing is jumping back and forth????

There is a performance gain, not sure how you're missing that in what everyone is saying in this and the other threads. The TPS on this, and well every, machine measures throttle position and alters the ignition map based on where, when and how the throttle is changing values, ie how you twist the throttle.

If you pull it, the bike will in fact run, however it will default to a "limp" mode with a reduced snap and general peppyness feel to it.

When I bought my bike I went dual sport road riding with my dad on his DRZ and I noticed the pulsing. So we pulled over, I unplugged the TPS and the surging went away but with a less "lively" feel to the bike. Plugged it back in and the bike felt better power-wise but still surged. All is in spec with the sensor so I just live with it surging a little.

Ymmv, however.

The bike is built for racing, is it not? That would mean it is not meant to be held at a fix thottle position for long periods (especily at the lower to mid RPM range); the bike is meant to accelerate hard, brake hard, then accelerate hard and so on.

From what I'm reading, this must be a common problem and obviously the manufacturer has overlook this as a problem. Do all WRs have this issue?

kloss450 i also done the same thing on my wr426, its moto trim and use it through my town and on ride outs, when connected it was a pain as it was a bugger for stuttering etc and not smooth, whereas as its disconnected it has full rev range with no stutter i can be at same throttle positions and its smooth with no sign of stuttering or anything, i have set mine to a switch for when i do back twisty roads i have it on and when through town and straight lines i have it off.

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