TPS disco... unanswered questions

28 replies to this topic
  • redrider77

Posted October 05, 2004 - 05:12 PM


I posted this in the WR forum, but only got two replies, both kinda vague.

***I know this is a very controversial topic, and after doing gobs of searching and reading, I can't tell what the latest concensus is on disconecting the TPS. I played around with disconecting mine today, and it was happiest unplugged.

I hear that there are some possible negative side affects, such as dry mouth, insomnia, sexual side effects... wait, that's Celebrex :cry: Predetonation and associated piston damage seemed to be the worst in particular that I found, but that was "a theoretical possibility".

Anyone know of any factual instances when running their bike unplugged (TPS) led to something bad? I'm trying to seperate the fact from the fiction here.***

Hopefully some more insight can be had over here. Thanks guys.

  • Fastest1

Posted October 05, 2004 - 05:31 PM


FFR or RHC would probably be able to give you any technical info, but from what I understand there are no side effects. It is smoother, I believe it has a slight amount more power and Tim Ferry's 426 never had one! :cry:

  • SteadySeniorRide

Posted October 05, 2004 - 05:40 PM


Hi Red.
Somewhat apples vs oranges, because I ride a DRZ400-S, but get this: Every piece of TPS information I'v read, from various web sites & not just TT, has said the same thing... that unplugging it had no adverse affect. I usually feel pretty secure when an opinion develops into a consensus.
Feel the power curve, feel the throttle, listen to the bike, look at the plug. If all systems are go...then go have fun.
For more accurate info on your specific model, maybe check in with one of the Yamaha Gurus on TT. Also, do a bunch of TPS searchs in your bikes forum class. Patch the bits & pieces of info together, and it's amazeing what you can somethimes learn.
Just trying to be helpful, not authoritative.
Good luck.
SSR :cry:

  • redrider77

Posted October 05, 2004 - 05:53 PM


Thanks SSR. I did search the WR forum pretty extenisvely (when I probably should have been studyin for class) and came up with the conclusion that everyone says/thinks something different. The one thing I didn't come up with is someone who could say "yes, i know of an actual instance when someone unplugged their TPS, and their bike exploded... or at least ate a piston." :cry: So far mine likes to be unplugged, but I will keep looking. :cry:

  • yzf450jack

Posted October 05, 2004 - 06:56 PM


I leave mine pluged in It has control of your timing to maxamize your horsepower I like the hit :cry:

  • SteadySeniorRide

Posted October 05, 2004 - 07:12 PM


Interesting. If so, I did not know it worked in conjunction with your timing. But then again I'm on the Z400S, and have felt no ill effects. I also admit, I'm not a final authority. Thanks 450jack.
SSR :cry:

  • Chris_from_Oz

Posted October 07, 2004 - 05:32 AM


I leave mine pluged in It has control of your timing to maxamize your horsepower I like the hit :cry:

If you read FFRacing's original posts about the TPS, you would better understand his findings at the time. I couldn't find the actual posts to put up a link here, but basically the dyno' charts indicated that the bike with TPS connected had what was construed as a noticable 'hit' in the powerspread. Then when the TPS was disconnected, the 'hit' seemed to be gone/reduced, leading people to think (by seat of the pants dyno') that the bike wasn't making as much power. The facts as I recall them were; just prior to the 'hit' on the dyno' chart with TPS connected, there was a noticable 'dip' in the power, only a brief dip, but a dip none the less. Then when the power picked up where it left off, it created an illusion of a big 'hit' in the power, when in actual fact, it was only because the power dropped momentarily, then abruptly resumed, that it seemed to have a hit. When FFR ran a dyno' run with TPS disconnected, the 'dip' in the power was gone, therefore no false feelings of a 'hit', just smooth seamless power right through the rev' range. This was quite a while ago that I read this, but I beleive I remember the facts correctly. After reading it I disconnected the TPS on my 426, and have had no drama since, just a nice, uninterrupted spread of power. Even smoother since fitting the 450 cam. :cry: Hope this helps :cry:

  • YZFan

Posted October 07, 2004 - 06:14 AM


Just my 2 cents! Mine has been unplugged for over a year now (installed an Edelbrock carb no TPS mount) no problems and couldnt be happier. Good luck

  • SteadySeniorRide

Posted October 07, 2004 - 08:53 AM


To Chris, in the land of somewhat "down-under."
Helluva good post, re: the TPS. :cry:
SSR :cry:

  • SureBlue

Posted October 07, 2004 - 11:24 AM


Chris, would I benefit the same unplugging TPS on my 450?
I have a 2-hour race coming saturday and would need some softer power. :cry:

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  • Fastest1

Posted October 07, 2004 - 11:32 AM


The only way you will know is to try it. It takes seconds to do and if you dont like it, plug it back in. I would test it before a race though. FFR also tried it on the 450, but I cant remember the results.

  • RippinInColorado

Posted October 07, 2004 - 12:42 PM


I recall the FFR posts just like you described, Chris, unplugging the TPS eliminated a dip at 4000-5000rpm or so. I disconnected mine and left it that way for the past few months. I recently read something that said the TPS's primary goal/effect is to eliminate detonation near the rev limiter. I plan to plug mine back in for this weekend's ride. The difference is so slight that I'd rather be safe than sorry.

  • yzf_rider400

Posted October 07, 2004 - 05:41 PM


I've got a question as well regarding the TPS. I tested mine today and it was putting out a resistence of 4.7 kilo ohms (within spec) but it would not change at all when the throttle was twisted (did the same test with the TPS on and off the carb). The manual says to replace the TPS, but I'm not sure I really need a new one. I've got it disconnected now.

The ohm resistence is suppossed to go from 0 to 5 (plus or minus 1) from closed to open throttle. If the TPS is removed does the ohm resistence increase infinitely?

If yes, have you heard of anyone setting it to 0 by using a wire bridge between the positive and negative terminals on the wire coupler (harness/black box) side?

Any specifics or additional information would be extremely appreciated! :cry:

  • grayracer513

Posted October 07, 2004 - 09:46 PM


I don't know where your information came from, but the TPS coil resistance listed in the manual between the blue and black leads is 4000-6000 Ohms. The resistance from either of these to the yellow is variable, but not specified. You are probably confusing the 4-6 VOLT output fed to the TPS at the blue lead. (all these specs and wire colors are true for a '03 YZ450)

In general, a TPS works like this: The TPS is a potentiometer, a type of variable resistor. The ignition module sends a 5 volt reference signal to the TPS and reads the voltage at the other end of the circuit when it comes back. If it sees 5 volts, it assumes a closed throttle. If it sees zero, it assumes full throttle. The third wire of the TPS is connected to the throttle so that a variable amount of electricity is shunted to the yellow wire, instead of passing from blue to black (using YZ colors). The module reads this changing voltage and uses it to determine throttle position. This information, combined with the tach signal, is what the module uses to vary the ignition timing. Voltage or voltage drop can be read at any one of 3 points, depending on how the system is set up, but that's the general idea.

When the TPS is disconnected, the module simply assumes the throttle is always wide open, and sets the timing accordingly, or goes to a base timing routine using RPM only, depending on the module's firmware. Don't do the trick with the resistor.

Additionally, disconnecting the TPS has never been cited as an improvement to any bike other than the '03/'04 YZ450F, so the mod info doesn't apply to earlier bikes such as yours, but you could try it

  • SureBlue

Posted October 07, 2004 - 10:13 PM


Some riders rob power from TPS for their lights, they put a halogen headlight and LED taillight that allows them pass the requirements to enter an enduro competiton where lights are must. Cheap way compared to a new stator.
Does this confuse the normal TPS function?

  • yzf_rider400

Posted October 07, 2004 - 10:35 PM


I'm using a manual.

The manual says that the TPS resistence should be between 4000 and 6000 and that the resistence should change between 0 - 5 +- 1 when the throttle is twisted (gruadual change).

So the resistence should be at 5000 when the throttle is closed? Does that mean the timing goes from a retarded timing state to a "regular one" as you twist the throttle?

Any more information is appreciated!

My TPS was not changing resistence it stayed at 4700.

  • Fastest1

Posted October 08, 2004 - 06:33 AM


gr513, It was stated by FFR, he even had dyno sheets on the runs back to back and it was for 426's also. :cry:

  • Chris_from_Oz

Posted October 08, 2004 - 07:14 AM


Chris, would I benefit the same unplugging TPS on my 450?
I have a 2-hour race coming saturday and would need some softer power. :cry:

Yep, FFRacing has done the mod' on both the 450, and the 426 I believe, with similar results. :cry: As 'Fastest 1 posted;

It was stated by FFR, he even had dyno sheets on the runs back to back and it was for 426's also.

I have had mine disconnected for well over a year now, and haven't experienced any ill effects at all, no detonation, it's all good :cry: IMO the majority of tuning problems with these engines are jetting related initially. Once you have your jetting dialled in, it's just a matter of playing with the fuel screw (fit an adjustable one like a Kouba/or similar for quick adjustments) to suit temp'/altitude. My point here is, if anyone who has disconnected their TPS is having ridability issues, it's more likely to be jetting/carb' setting related, than the TPS mod'. Simply my opinion of course :cry: :cry:

  • SureBlue

Posted October 08, 2004 - 07:43 AM


Thanks Chris, loaded the bike already in my van, leaving morning at 6. I have the adj. fuel screw and opened it a quarter turn, it's gettin chilier here already. Will try disconnecting TPS before nxt practice, don't want to do it right prior to race. Never had any jetting issues though, bike always starts easy, even after a stall :cry: or dive :cry:

  • Chris_from_Oz

Posted October 08, 2004 - 07:46 AM


Good luck for your race meet :cry: :cry:

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