(mal)adjusting the TPS

Tech-types -- this question is related to the thread in Technical/Mechanical Problems about the '07 stumbling on acceleration problem. What if? the tps was set to a different value than stock? Would the cpu be tricked into thinking the throttle butterflys were, say, more open than they actually were and tell the injectors to feed more fuel? Is an adjustable tps a tuning device?

If this has been covered previously, I apologize (haven't seen it) -- please link.

If any of you 'knowledgeable ones' know or care to speculate....tia.

Would mess with the ECM's calibrations. For example, the ECM sees 15-17 as idle, sets mixture appropriately. Get over 17, starts looking for map sensor inputs and uses motorvation mix settings since the bike would be in motion at this point under normal circumstances, the TPS shows desire, the MAP workload, and the Crank Sensor (or Tach) actual rpms. Since all are taken into account, erroneous signals from any of the sensors starts skewing the system, with sometimes predictable, but rarely pleasant, results.

I see Rad's back!! Since I was writing this as Rad was posting, I will add it anyway

What if?...Would the cpu be tricked into thinking the throttle butterflys were, say, more open than they actually were and tell the injectors to feed more fuel? Is an adjustable tps a tuning device?

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Reader's Digest Condensed Version: Yes. No.
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The rest of the story:

The TPS job is to tell the Electronic Control Unit (ECU a.k.a. computer) what the throttle is doing. The TPS sits on the throttle body rack and is coupled to the throttle plates so that the TPS shaft rotates in lock-step with the throttle plates. The TPS has a fixed span (difference between minimum resistance and maximum resistance), only the location of the wiper can be varied by twisting the body of the TPS during calibration. Before adjusting the throttle position sensor, the engine idle speed must be properly adjusted. If you set the TPS wiper so that it is indicating the throttle is open more than it really is, then it will tell the ECU you are at wide open throttle before you are actually there, negating fuel enrichment over last several degrees of throttle rotation.

The ECU supplies GND and +5 volts to the TPS. Picture a resistor with 5 volts on one end and ground (0 volts) on the other end. At idle there is a contact (wiper) touching the resistor *almost* on the ground end of the resistor. As you twist the throttle the contact slides up the resistor toward the 5 volt end such that the voltage climbs linearly as the throttle is twisted. The ECU does a conversion so that 0 volts = 0% throttle and 5 volts = 100% throttle. At idle you need a bit of throttle to keep the engine running -- which is done by the throttle stop adjustment. The throttle stop adjustment also moves the TPS wiper up the resistor a small amount, enough to produce .75 volts. When you see 15 on the diAG screen you are seeing 15% of the 5 volts or .75 volts on the wiper of the potentiometer (the resistor); at 50% there is 2.5 volts on the wiper; at 97% there is 4.85 volts on the wiper.



You can see how the TPS is constructed here.

Edited to add:

(mal)adjusting the TPS

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Accurately said!! You would be mal (in Spanish = badly) adjusting the TPS. This is diffrent from (MIS)adjusting the TPS :blink: :lol:

Thanks, I liked the Reader's Digest version. But seeing the expanded version gave me great comfort to the credibility of the abbreviated answer.

Don't mess with this. I guess you could add a bias voltage or slightly adjust to make the ECU think the plates are more open, but clearly the maps we put in our PCIII's do not indicate that an even richening is needed.

Why piss uphill? Get a PCIII and your worries go away forever. Don't think of it as additional money. Just add it to the price of the bike and be happy mon!

-BD

BrunDog said:

Don't mess with this. I guess you could add a bias voltage or slightly adjust to make the ECU think the plates are more open, but clearly the maps we put in our PCIII's do not indicate that an even richening is needed.
Why piss uphill? Get a PCIII and your worries go away forever. Don't think of it as additional money. Just add it to the price of the bike and be happy mon!

-BD

Click to expand...

A good engineer could make piss run up hill.

B)

Thanks guys for the good, insightful, advice. We'll let you know what happens. We don't want to make anything (that's not supposed to) run uphill -- but, are going to solve this driveability issue.

We don't have an '07 shop manual, yet -- and the part number of the '07 computer is different from the '06 cpu part #. And, we all know the system is totally diff. -- gen 1 to gen 2.

Yesterday I, coincidentally, had lunch with a friend who rides a V-Tec VFR and he said it had 'un-solveable' driveability problems that were only resolved with the installation of a PCIII: plug it in -- all 'goodness and light' from then on.

So, BD, as much as I resist going aftermarket -- the dictates of the EPA may be forcing this?

Thanks again, all.