Undoing an electronic TPS reset on a non linear TPS model - in this instance an ST4S

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An issue that comes up with the 59M and 5AM ecu models is the electronic TPS (Throttle Position Sensor) reset capacity the diagnostic tools for these ecu have.  The electronic TPS reset is specifically for linear TPS models.  It has no place for non linear TPS models, but is often performed when it shouldn't be by people who have no idea what they're doing, and can cause issues as it overrules the underlying throttle opening to TPS output relationship to some extent.

How I don't actually know, I don't have the knowledge to understand what the software does when things that shouldn't be done are.

For those who aren't aware of the differing TPS styles and setting procedures, there's some info here:

4V Non linear TPS setting
4V Non linear TPS setting video 
2V Non linear TPS setting
2V Non linear TPS setting video
Linear TPS setting

On to the story - A fellow from interstate emailed me about his poor running ST4S.  The ecu had been reflashed by a Rexxer agent for the previous owner.  He had had it back to the Rexxer agent, who had performed a TPS reset via a diagnostic tool as he had also done when it was originally flashed.  It was no better afterwards.  In my experience the ST4S 59M Rexxer file is pretty good, so there should have been improvement to be had.

I replied that firstly, he needed to undo the electronic TPS reset.  The first time I came across this was a 2002 M900ie that was showing 3 degrees throttle opening on the diagnostic tool @ 700mV TPS output.  I had no idea what to do to fix it, but started guessing at what might help.  Given that flashing the ecu with my CDC tool tends to reset most background settings, I figured I'd try that.  So I read the file from the ecu and then flashed it straight back in again, just to make sure nothing else changed.

After that, the TPS voltage output to ecu diagnostic throttle angle relationship appeared to be about right.  I then carried out the appropriate non linear TPS baseline procedure and the rest of the tune set up and it was then fine.  Well, as good as a std ecu 2002 M900ie can be.

To do this himself, I recommended he download the Guzziddiag IAW5XReader and IAW5xWriter software from here and buy the required cable from Lonelec here for a guaranteed working set up. I also asked that he carry out each step of the process individually, and ride the bike afterwards to see what actually worked and what didn't as such, and provide me with the feedback.

Feedback as follows:

I reflashed the ECU with its original file as you suggested.  Bike ran better immediately. Misfire/stumble gone.

This was the part I was mainly interested in.  A simple before/after only related to the ecu reflashing, and it worked as I'd hoped.  The next part of it was the baseline TPS set up, and the impact of that depends on what has or hasn't been done previously, and how well (or not).

We then followed very closely your video and blog on the TPS reset.  The TPS looked new…no paint to be found at all  and had Allen screw heads.

The initial idle throttle angle was set at 1.6 deg.  With fast idle connection off etc it dropped to 1.3.  Backed out the butterfly throttle adjustment as directed.
We reset the TPS back to zero….played with this setting to ensure we were on zero and not under, as we were relying on the diagnostic tool we only had degrees.  We minutely jiggled the setting up to 0.1 and 0.2 degrees then noticed tightening the screws brought it back down a tad to zero.

So I am guessing its now pretty close.( If we had used voltage it might have been easier).  Reset the idle at 2.6 degrees (USA Bike).  Refit the fairings and took it for a brief ride.

Huge improvement.  Smooth throttle response from low revs.  Engine tone is different, no backfiring or popping on deceleration.  Idle is better, smoother.  Slow commuter speeds much improved second and third gear 3000 rpm cruising very acceptable.

Again, an improvement as hoped and generally expected when the baseline is done properly.  It really disappoints me that so many of these bikes aren't set up right, and the rubbish reputation they get as a result.

Thinking about it now, as another possibility, you could also try doing another electronic reset to confirm what throttle opening value it resets to.  Then perform the TPS baseline set up procedure, but finish by setting the TPS output voltage to the theoretical corresponding voltage for the required throttle opening.  Ie, 2.4 degrees = 404Mv, 2.6 degrees = 423mV.  Then do another electronic TPS reset.  I wonder if that would also work.  Maybe someone can try it.

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