Throttle sensor


35 replies to this topic
  • grayracer513

Posted August 31, 2006 - 09:11 AM

#21

Here's the deal with the TPS. Most, if not all, electronically controlled ignition and fuel systems use one to gauge engine load. The more advanced ones add a manifold pressure sensor to get a more exact picture of the situation. They also use a tach signal to read the engine speed. With this info, the control module decides what the ignition timing should be.

The TPS is set up so that it sends a voltage back to the ECM that varies with the throttle opening, and all of them that I can think of right now are set up so that high voltage is a closed throttle, and low voltage is an open throttle.

What the normal response to a more closed throttle at higher speeds is is to advance the timing more than it would be at full throttle to improve part throttle power and fuel economy, exactly like the vacuum advance units on older car distributors did. While the max ignition advance on an engine might be something like 34 degrees at full throttle with the revs up, the max advance at cruise might be as high as 50-60 degrees. The reasons are a little complicated and relate to dynamic compression, but that's what happens.

If you unplug a TPS, the voltage returned to the ECM will be zero. The ECM will respond to that either by seeing it as a fault and entering a default mode of operation with fixed timing, or by simply seeing it as full throttle all the time, and going about its business as usual. Most modern systems react with a combination of the two; they complain about the fault, but continue to control what they can based on the information they have. The peak power increase that Tryce has shown indicates that YZF CDI clearly changes the full throttle timing when the TPS is unplugged, but you might get similar results by adjusting it. You could also make it ping at part throttle that way, though.

The choice to have an open (unplugged) TPS be full throttle is both deliberate and important. If the assumption is that the throttle is open, and full throttle requires less advance, the engine will still operate safely at full throttle, and only part throttle operation will be negatively affected because the timing will be retarded from the optimum levels.

As far as the '03 YZ450 specifically, I find it pretty interesting. I can't and won't argue with T-Dub's results; they are what they are. But my '03 does not have the dip in its power curve that it did when it was stock, and the TPS is still plugged in. I made it go away by putting the FMF Power Bomb on it. It comes back if I use the stock header with either the FMF or the stock muffler, although it's worse with the stocker. Based on my understanding of how the PB works, my guess is that there is a complex situation involving the exhaust system pressure levels during the overlap event at that speed that is helped by changing the advance curve slightly, and that is changed by the PB header, but I have no tools at hand to verify that.

I leave mine connected because I like the way it runs as is. If it did work so well, I'd fool with it.

  • motokid338

Posted August 31, 2006 - 11:18 AM

#22

well right now the one i have on there is broke anyways so im getting a new one and seeing what its like when its on...


I hope that i starts esaier with it on becuse i had the mechnic look over the whole bike for anything that might be causing so hard to start... he drained the carb bowl.... he put in a little bit smaller jets.... this is the last thing that i can think of that would cause the problem of terrible throttle response and extremley hard hot starting... i know it's a big four stroke but the dealer said it shouldent be this hard to start... the only way it will start once hot is letting it sit for 15-20 minutes. I have a hot start but it doesnt seem to do anything.... I hope that this is the problem becuse theres is absolutley nothing else wrong with the bike... the do have a pro circuit ti-4 system but that and the jets and hot start ore the only after market things on there. :thumbsup: :applause:

  • T H O R

Posted August 31, 2006 - 12:01 PM

#23

well right now the one i have on there is broke anyways so im getting a new one and seeing what its like when its on...


I hope that i starts esaier with it on becuse i had the mechnic look over the whole bike for anything that might be causing so hard to start... he drained the carb bowl.... he put in a little bit smaller jets.... this is the last thing that i can think of that would cause the problem of terrible throttle response and extremley hard hot starting... i know it's a big four stroke but the dealer said it shouldent be this hard to start... the only way it will start once hot is letting it sit for 15-20 minutes. I have a hot start but it doesnt seem to do anything.... I hope that this is the problem becuse theres is absolutley nothing else wrong with the bike... the do have a pro circuit ti-4 system but that and the jets and hot start ore the only after market things on there. :thumbsup: :applause:

This is kind of a over looked thing, but you're spark plug. I had my original one in all year, it was getting hard to start, so I changed it out, and it's starting right up, first kick.

  • motokid338

Posted August 31, 2006 - 01:52 PM

#24

i checked my spark plug and it sparks fine the only time it's hard to start is when it's hot (more than a normal four stroke) :thumbsup: I dident think that that the TPS had anything to do with this. :applause:

  • mj2412

Posted September 01, 2006 - 05:17 AM

#25

Hello,

try first an new spark plug and then a new spark plug connector. Maybe it isn´t fitting perfect anymore and a very hot spark plug will not work properly and then you have to wait until it cools down before you can start it again. At least a spark isn´t enough to tell you that it works. Most of the time when i flooded my bike, the spark plug sparks fine, but the bike wasn´t able to start. Still after cleaning it wouldn´t work, until i put a new plug in.

Luckily i flood my bike only once ore twice a year.

Martin

  • motokid338

Posted September 01, 2006 - 10:22 AM

#26

I put on a new spark plug so i hope it works but i dont see how the TPS would effect starting a hot bike :thumbsup:

  • motokid338

Posted September 15, 2006 - 12:36 PM

#27

Ok.. i got my back back from the dealer today with the new TPS.. they said that it starts when hot a lt better but it has a very low back pressure to the motor.. i dont know if it's becuse of the ti-4 wich im putting in new packing but thye ran every test that they could and every thing was perfect... the whole electrical system was also perfect.. so i get home and start it.. it starts on the first kick... then i let it idle for maybe 2-3 minutes and shut it off and try to start it again and it wouldent start back up... I am out of ideas so our the mechanics... :applause: :thumbsup: :applause: :applause:

  • grayracer513

Posted September 15, 2006 - 12:59 PM

#28

they said ... it has a very low back pressure to the motor..

They said what?

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  • motokid338

Posted September 15, 2006 - 01:05 PM

#29

It has low back pressure :thumbsup:..... im replacing the packing in my exhaust becuse they said that could cause that... but thats not why it wont start after it warms up.. i just got it started agian and as soon as a let go of the throttle or stop reving it it stalls out... but then when o go to start it agian it wont :applause:

  • grayracer513

Posted September 15, 2006 - 01:15 PM

#30

Backpressure has nothing to do with it. Get it running, get it to idle, and adjust the idle mixture to spec. Then see how it starts.

Are you sure they didn't say, "low compression"?

  • motokid338

Posted September 15, 2006 - 01:22 PM

#31

he said it has low compression due to low backpressure from the exahaust... i dont really want to put the stock back on but idk if ill have to :thumbsup:

  • grayracer513

Posted September 15, 2006 - 01:59 PM

#32

he said it has low compression due to low backpressure from the exahaust...

The first and most productive thing you can do, if you can't solve this on your own, is to find a different mechanic. The one you are currently using is...(I had to stop myself there)...um, less than totally competent. You need to go somewhere else.

It may be down on compression, but that has nothing to do with the exhaust pipe. Mine has the same exhaust on it, and if there's anything it does NOT lack, it's compression. Assuming a healthy electrical system, and a good spark plug, almost all hot starting problems with early YZ450's fall into one of two categories: idle improperly set (or a related carburetor problem), or operator error.

  • motokid338

Posted September 15, 2006 - 06:39 PM

#33

I thought i was doing everything right but im still not used of a really big four stroke yet :thumbsup:

  • grayracer513

Posted September 16, 2006 - 06:18 AM

#34

Up to the current year, big YZF's are very particular about the routine used to hot start them. The thing with 426's is that they all start pretty much the same way, and anyone who can start theirs will be able to jump right on someone else's and fire it right off. 450's are different, and each one has its own little personality.

My own '03 likes the throttle cracked very slightly open on warm restarts, and if it was shut off normally, it doesn't usually need the hot start. If I stall it or drop it, it's different. It then likes a couple or three times slowly through compression with the throttle half open, then a couple of kicks barely opened over idle with the hot start. But each one is a little different, and you'll have to experiment a bit.

Getting the idle right is very important to getting the bike to start. If it won't idle, why would it start with the throttle closed? The black knob on the left side of the carb is the idle speed. Turn it clockwise to raise the speed, counter clockwise to lower. Find the idle fuel screw and turn it all the way in until it seats gently, then back it out 1 3/4 turns. Once running, turn the idle speed in until it will idle, then adjust the speed 'til it sounds right. Your bike should then start somewhat more easily.

If you need help, find a different shop to go to.

  • motokid338

Posted September 16, 2006 - 06:58 AM

#35

I think i will just have to get used of that bikes starting routine... my old bike did have it's own little starting routine but it wasn't this involved...

  • ttxpc

Posted October 12, 2006 - 03:29 AM

#36

A friend of mine just bought a YZ426 and is having the same problem, just tonight he switched off and no kicking would revive the beast until about 10-15 mins had elapsed, would fire a little and die out, Even my old 96 Husky wr360 fires right up after 1 or 2 kicks even on todays 35 deg heat (celcius...) :devil:





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