TPS disco... unanswered questions

well, I am indeed a dumbass. I read my manual a little more carefully today and saw that the resistence is suppossed to change while testing using the black (or blue can't remember now) and the YELLOW wire.

I'm going to try it again. Thanks for the info grayracer!

After testing my TPS resistence from closed to open, my bike goes from 4400 to 1160 ohms. The change is smooth, but shouldn't the range be from 5000 to 0 (plus or minus1). Even if 4400 is a suitable closed resistence shouldn't the range also drop the lower resistence evenly by 600 in this case resulting in a definite 0? :cry:

Or can the plus/minus 1 be added or substracted at either end of the spectrum? (I'd still be .16 kilo ohms out of spec)? The manual goes on to state that the ranges can vary. Is the TPS only checking for a few throttle positions and not a smooth range? Does the black box adjust itself for varying resistence outputs?

All right enough questions. I await thy divine knowledge. :cry: :cry:

The values given in the manual for the full closed position is from O up to 2000 ohms, so your reading of 1160 is in spec. Also your reading of 4400 ohms for full open is in spec. Watching the VOM as you move the TPS, there should be no sudden rise or fall (or open/shorted) spots, and the change in resistance from one end to the other should be fairly linear. There may be a range of motion at either end that does not show a change in resistance in some cases.

It is important to be sure that you take these readings between the black and yellow leads. If you use the blue and yellow, your values will be reversed, and blue to black you'll get no change as you move the TPS. Your manual should have a schematic in the front of the section that may help understand this.

The readings you posted are fine and are well within tolerances. Most electronic devices are made to work at about a 10% precision level, so I don't know where the +/- 1 came from. According to the manual, they want any number between 0-2000 at one end, and 4000-6000 at the other. Only when one reading is outside of those ranges is it unacceptable.

I think you're over-worrying the issue a little. Remember that the ignition module is not reading resistance, it's comparing voltages at these wires, and you don't get to see the circuitry inside the box. Your TPS checks out OK.

Thanks grayracer513, your knowledge is much appreciated. I don't think my manual said the lower and upper ranges it just mentioned a range plus/minus 1.

I'm not going to worry about it then. I've been trying to track down a problem for a while now and I've eliminated everything except for my electrical and computer.

Once again, thanks! :cry: :cry:

I was working with a YZ450 manual. I see in my '01 250F manual that the specs are different for the closed resistance at idle, but they still run in a fairly wide range. Re-read yours to be sure of what they're telling you. Plus or minus 1 out of say 1000 is one tenth of 1% precision, which is both unachievable as well as totally unnecessary in modern digital electronics.

grayracer, my manual says the range is from 0 - 5 +- 1 kil ohms so the plus/minus one I think is referring to 1000 ohms. I tried it disconnected and connected and my stuttering problem persisted either way. I went on to disconnect my kill switch and that seemed to help quite a bit, but not completely. I went through all the electrical checks (listed in the manual at least) and found I had an incorrect reading for my secondary coil resistence. The manual says the range is 9.4 - 14.3 kilo ohms and mine is reading 21.6. Do you think this would be enough out of spec to give me ignition problems. I'm thinking it's either coil or CDI unit now.

Thanks in advance! :cry:

CORRECTION: oops, didn't pull the spark plug cap off before testing. I'm within spec (11.89). Damn, I was sort of hoping the coil was the problem. I've now speced out all the electrical tests and am left with the only possibility being the CDI unit (or possibly a frayed wire somewhere).

Anyone got a CDI unit (black box) for my bike, they'd sell?

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:

here's the link you're looking for


I have found zero long term effects to date from disconnecting the TPS. I have an Edelbrock carb on my 470 for over a year now. This carb does not have the TPS, or choke, or hot start for that matter.

I really can't comment on the effects this would have on power delivery, with the change in Carbs and other modifications I really never knew the difference if the TPS was unplugged or not.

I too disconnected the TPS on our 450 per the FFR findings and was pleasantly suprised with an additional 2 hp increase in the midrange (about where the "hit" starts) what appears to happen is the timing that is mapped through the TPS when connected is retarded at this operating range and then when full timing i.e.: full power is achieved the machine picks up noticeably, hence "the hit". When you disconnect the TPS you essentially default this map and I would presume take this ignition advance out of the equation and have full timing immediately and start making HP as well. The "hit" is the transition between the lower ignition timing / lower power to full ignition timing / higher power. When you run disconnected the engine makes more power sooner with no noticeable change ("hit") throughout the rev band, you are actually making more power and not noticing a "hit" but you will/should notice a better accellerating machine! :cry: Care to add anything Tryce?

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