GuzziDiag Stepper Motor Values

[wallyging]

I'm in the process of tracking down an episodic high idle on my 2007 Norge with 48,000 miles and trying to check the idle stepper motor to see if it is working as it is supposed to. Only problem is I don't know for sure what the various idle stepper readings (base, break, and controller) refer to and what their values should be if the stepper is working correctly.

Does anyone know what "stepper base", "stepper break" and "stepper controller" refer to?

With the engine cold at idle the readings start out around 100, 170 and 70 respectively. When the engine is fully warm the readings are usually around 100, 50 and 206. Off idle (1800+ rpm) with a warm engine the readings are 100, 100, 0.

Are these readings consistent with a properly functioning stepper motor?

[pete roper]

If you fully close the throttle and re calibrate the TPS to 4.6 or whatever and then start the bike does the TPS value rise to 5.0 or above?

[wallyging]

If you fully close the throttle and re calibrate the TPS to 4.6 or whatever and then start the bike does the TPS value rise to 5.0 or above?

I'll check tomorrow and let you know.

[wallyging]

If you fully close the throttle and re calibrate the TPS to 4.6 or whatever and then start the bike does the TPS value rise to 5.0 or above?

No, Pete, the TPS stays right at 4.7 to 4.8.

I started the engine cold (2C) this afternoon, let it warm up to 80C, and monitored the Engine Temp, TPS, RPM and Stepper Idle Break. Here's what I observed.

The TPS remained at 4.8 throughout.

Idle was around 1300-1400 RPM throughout. (see note about TB re-sync below.) When I blocked off air flow to the stepper motor RPM would drop about 100.

Idle Stepper Break started out around 130, but dropped to 50 within a couple of minutes, long before the engine had completely warmed up. The vacuum in the hose from the air box to the stepper motor was strong at 130, indicating it was flowing a good bit of air to the TBs, but at 50 there was still some vacuum. This suggests to me that the stepper motor never shuts off completely. When the engine RPM exceeds 1800 the idle stepper break goes to 100, pulling a fair amount of vacuum.

After I took the readings I re-synced the TBs and reset the TPS - only small tweaks were needed. With the engine running TPS now read 4.7 and RPM was 1250. When I plugged the air box hose to the stepper motor there was no significant change in idle. Perfect! I took the bike for a ride and the idle behaved as it should, but I need to put on more miles to be sure the stepper is working correctly.

Bit of background....  Prior to today I had removed the TBs and cleaned them thoroughly with carb cleaner - the butterflies, passages and hoses to the stepper motor, and the air flow screws/passages. I ran a lot of carb cleaner through the stepper motor (spraying into the hose from the air box) with the bike both stopped and running, and then cycled silicon lube through (turning ignition on/off). I wish now I had taken stepper motor readings before I cleaned everything to see if indeed the values changed. Assuming the problem is fixed, I'm guessing that gunk in the stepper motor had kept it from turning freely and consistently, and sometimes didn't allow air flow to drop all the way down to 50, which seems to be the intended level of air flow at idle.

I believe the Stepper Idle Break readout in GuzziDiag refers to the "step" the motor is on (stepper motors turn their shafts in precise steps), which regulates the amount of air to flow to the TBs, more air at higher steps and less at lower steps -- only Moto Guzzi know the precise amount. Stepper Motor Base always reads 100, and I think that is where the motor sits when it is not activated. Stepper controller values appear to be instructions from the ECU to the stepper to tell it how many steps to move from the base. For idle break values above 100 the controller tells the motor how many more steps to go up (e.g., controller value of 30 tells the motor to go to step 130). For idle break values less than 100 stepper controller values all seem to be in excess of 200 which puzzles me (e.g., controller value of 206 results in idle break of 50)

[Pizza Guzzi]

Just thinking out loud here - since it appears the stepper motor never completely shuts off air from entering the engine would there be an issue with running rich for those who block off the air hose supplying the stepper motor since the ECU thinks there is more air entering the cylinder ?
Maybe I should just take a nap !

Glenn.

[wallyging]

Good question, and I don't know the answer, but assuming that its normal for the stepper motor to never shut off air flow completely (at idle or off idle) Guzzi surely would have taken that into account in how they mapped the fueling.

[pete roper]

Lambda sensor should trim around it.

[beard]

Lambda sensor should trim around it.

But not at idle.

If the stepper is on one of his borders during idling,
the only way is to adjust the bypass screws until the stepper is able to regulate again.

[pete roper]

OK, I thought Lambda input was working at idle. My mistake.

Pete

[wallyging]

But not at idle.

If the stepper is on one of his borders during idling,
the only way is to adjust the bypass screws until the stepper is able to regulate again.

What is a border?

[pauldaytona]

What is a border?

read that as outer position.

[wallyging]

read that as outer position.

Not sure I follow. Are you saying if too much air is flowing to the TBs through the bypass screw(s), or the butterfly of the right TBs is too far open, or the TPS is too far off, the idle stepper cannot get the motor to idle correctly?

[wallyging]

For idle break values above 100 the controller tells the motor how many more steps to go up (e.g., controller value of 30 tells the motor to go to step 130). For idle break values less than 100 stepper controller values all seem to be in excess of 200 which puzzles me (e.g., controller value of 206 results in idle break of 50)

I think I've "cracked the code" of stepper idle controller values...   Stepper controller values appear to be instructions from the ECU that tell the stepper motor which step to move to. For idle break values above 100 the desired break value is the controller value plus 100 (e.g., controller value of 30 tells the motor to go to step 130). For idle break values less than 100, the desired break value is the controller values minus 156 (e.g., a controller value of 206 results in a break value of 50).

My experience suggests that a break reading of 50 is normal for fully warmed up motor. I'm hoping this information will be useful for members who would like to know if their stepper motor is operating normally.