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Stepper Motor Bypass

Yeah, the stepper motor is a fast idle system. It adds extra air to be combined with the extra fuel the ecu is adding
 
That makes sense ... your opening the air passage more on the stepper and adding more fuel for a faster idle!!!

Interesting is on the VDST software I would see the stepper value go up and down ....at the same beat as the irratic engine till the temperature would reach more or less 50 deg C.
Afterwards the stepper motor value would be stable at 80 or 90, the engine would run smooth ..... and slowly the stepper value would decrease.
More the engine was getting hot more the stepper value was decreasing ..... closing :eek: found that weird :huh:
Unless there again one would say the fuel delivery changes when the engine is hot!

I'd understand when the engine is cold ... fast idle .... A/F delivery and all but why would you control, at idle, 2 parameters the idle control valve and the fuel delivery when engine is hot? (That complicates things don't you think? :silly: )
 
It is also supposed to reduce engine braking in high rpm by opening a tad the steppers, as I understand so far.

Nevertheless, it seems that the cold idle feedback loop is not optimized by the ECU programmers.
 
Here’s another thought again :lol: ……the stepper motor has to keep the idle constant and has to be able to travel (open and close) enough from one upper limit to the other lower limit. (In other words the step values that were taken during the test 51 being close and 200 being open)

So when I did the test I can assume that when you start the engine cold the stepper motor value should be lower than 200 and when the engine is hot the stepper motor should be higher than 51.

When we sync the TBs everyone including the Mother Guzzi specifies to close the by-pass screws. Doing so you are asking (electronically) the stepping motor to self-adjust and compensate for an idle of 1200 rpm.

My theory would be when balancing the TBs (engine hot) the by-pass screws have to be adjusted to reflect the stepper motor value (Ideally 100) or else you may have rough idle if at its limits.
Would this make sense?

Update the 30 Aug:
Re-checked the TB sync of the bike and was able to adjust the stepper motor value close to 100 (at idle) by slightly adjusting the by-pass screws on both TBs.(while engine hot)
Start with the by-pass screws closed! ..... with the VDST stepper value at 130 I slighty opened the by-pass on the right TB and rebalanced my gauge to 0 with the left by-pass TB. Doing this the stepper value decreased.
Then re-balanced at 3000 rpm with the TB set-screw.
Did this a few time and the final result were...... Idle was balanced with stepper motor value 94 and balancing gauge were close to 0.
At 3000rpm balancing gauge +/-1cm also. :)
 
DanPez said:
Here’s another thought again :lol: ……the stepper motor has to keep the idle constant and has to be able to travel (open and close) enough from one upper limit to the other lower limit. (In other words the step values that were taken during the test 51 being close and 200 being open)

So when I did the test I can assume that when you start the engine cold the stepper motor value should be lower than 200 and when the engine is hot the stepper motor should be higher than 51.

When we sync the TBs everyone including the Mother Guzzi specifies to close the by-pass screws. Doing so you are asking (electronically) the stepping motor to self-adjust and compensate for an idle of 1200 rpm.

My theory would be when balancing the TBs (engine hot) the by-pass screws have to be adjusted to reflect the stepper motor value (Ideally 100) or else you may have rough idle if at its limits.
Would this make sense?

Update the 30 Aug:
Re-checked the TB sync of the bike and was able to adjust the stepper motor value close to 100 (at idle) by slightly adjusting the by-pass screws on both TBs.(while engine hot)
Start with the by-pass screws closed! ..... with the VDST stepper value at 130 I slighty opened the by-pass on the right TB and rebalanced my gauge to 0 with the left by-pass TB. Doing this the stepper value decreased.
Then re-balanced at 3000 rpm with the TB set-screw.
Did this a few time and the final result were...... Idle was balanced with stepper motor value 94 and balancing gauge were close to 0.
At 3000rpm balancing gauge +/-1cm also. :)
Click to expand...

This is a very old thread. Is there a test to confirm the stepper is working? If your stepper cycles at key off, does that prove it is working?
 
nose2wind said:
This is a very old thread. Is there a test to confirm the stepper is working? If your stepper cycles at key off, does that prove it is working?
Click to expand...
I would say that only proves part of the question. The stepper has to flow air, not just cycle. If the air passages in the stepper are blocked it will still cycle.
What is your issue? Why do you think your stepper motor may have an issue?
If you squeeze the hose leading from the stepper to the airbox, blocking it off, it should make a difference causing the idle to drop (especially when cold).
There may be additional tests spelled out in the manual.
 
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