Motobene
Well-known member
IF YOU CAN SOLVE THIS LITTLE PROBLEM YOU ARE AWESOME... AND DAMNED SMART!
The bike in question is my wonderful 2019 Beta 390 RR-S, but I suspect the problem would apply across all the FI model years many model years. It is not a common problem at all and I've never seen it mentioned or detailed anywhere in the internet, and no fault code is generated.
WHAT HAPPENS
Intermittent complete loss of idle when the throttle is closed, which then of course includes the loss of the very appreciated timed ramp-down to normal high idle to reduce the problem of immediate engine braking. Once the problem starts, and I can tell immediately because there is over-aggressive engine braking, if I then leave the throttle closed and slow to a stop, the rpm will descend to a stall with the little ticks of the engine starting decompressor function kicking in. As I roll to a stop dead engine I catch a wif of over rich fuel condition, which shows the injector pulses are still active and effective, but there's not enough air to allow fuel burn. I know ignition is fine because if I crack the throttle open to give it more air the engine fires back up.
WHAT TRIGGERS THE PROBLEM
Throttle being closed after modest to hard acceleration. Maybe 1 out of 20 times. Riding around gently will not initiate the problem.
WHAT CORRECTS THE PROBLEM
Pushing through the loss of idle and loss of the timed ramp-down to idle, with some cursing, and the ECU will eventually regain a kind of equilibrium and restore to normal idle. Or just roll to a stop and cycle the key off and back on and restart. If I roll to a stop after dying and then try to start the bike without cycling the power, the bike will not want to start throttle closed, as there is loss of idle bypass air. Throttle more open will allow the bike to start, but it will be balky and over rich because the TPS tells the ECU to add fuel on top of an already over-rich situation.
WHAT IS APPARENTLY HAPPENING DURING THE PROBLEM
The idle bypass stepper motor pintle drops to close off idle air, perhaps all the way to the throttle body seat.
ANALYSIS
The ECU is the brain and the stepper motor is a slave to it. The effect of the intermittent fault manifests in the stepper, which is commanded by the ECU. The ECU makes decisions of what the tell the stepper from inputs like mass-flow sensor and TPS. A new TPS was fit, so that's not it. The Beta mechanic said he swapped to a different mass flow sensor, no change. I think he also swapped the stepper? Hmm.
DO I UNDERSTAND THE SYSTEM?
A good start, no? Check me and correct me, please.
The idle bypass air control is via a 'stepper motor' that works on motor rotation based on stepped current inputs by the ECU. A 4-wire idle bypass so there are two DC motor coils (phase A and phase B - ECU pins D3 & D4, and C4 & E4), one coil for turning the motor armature one way a certain number of step counts, and a separate coil for turning the motor armature the other way a certain number of step counts. On the end of the armature is a threaded shaft screwed into a rounded-end-cylinder-shaped thing called a 'pintle' that does not rotate. When the one motor turns the shaft one way, the pintle extends, and the other way the motor makes the pintle retract. Motor rotation and pintle extension/retraction response is super fast. There are no additional wires to provide the ECU with absolute position feedback and it can only command the pintle to move based on the number of pulses to each coil. The stepper is oriented vertically, so the thing is either more up (more idle-air bypass), or more down (less idle-air bypass). And if the thing descends all the way to touch the throttle body air-bypass seat, NO idle air bypasses the closed butterfly valve and the engine, throttle butterfly closed, will die unless pulled along by the bike, in which case is accompanied by heavy engine braking.
How does the ECU know where the pintle is so that when starting it is positioned for the correct idle? I think it does this referencing off something known. I think when you cycle the power to the ECU it commands the pintle to overshoot the seat and either the ECU knows when the pintle hits the seat by change in current or resistance, or it's just so fast the command will overshoot and dwell some milliseconds, after which idle position is simple: to a pre-determined number of opening-coil step counts, as determined by other factors, such as temperature. For example, when the engine is cold (as in not-summer type cold), the idle will run high at first, and the time to ramp down to idle will be longer. As the engine warms, the idle comes down, and the timed ramp-down shortens to the running-temperature timed ramp-down, which is a real blessing by removing the traditional FI problem of heavy engine braking when the butterfly valve is shut. Brilliant!
How exactly the system works I can only infer from how it behaves, as finding tech documentation on systems like that of the Beta is like pulling teeth. Manufacturers like to keep that behind some proprietary wall of darkness, which doesn't help diagnosis when things go wrong.
ECU 1-HOUR SWAP
If a person local to Albuquerque would please come over with their close-enough Beta 031.40.015.10.00 ECU for 2019-ish bike, for a quick ECU swap I'd REALLY appreciate it! Buying an ECU and having the dealer program it ($600?), only to retain the problem because it's NOT the ECU would just make me puke. Update: If the problem continues to persist, just bit ethe bullet and buy a new ECU and have it programmed to the bike.
SENSOR?
Not the TPS. That's new. Beta tech said he did a swap of the of the T-MAP sensor with no change in the problem. RPM sensor? Two temperature sensors? These appear to all be working.
A PATCH?
Given cycling the power on and off immediately corrects the problem, I've been eyeing a 'patch' solution of some means to manually or automatically cycle the power off in a blink to the ECU at pin A4 (like turning off the key). I tried doing that with the engine stop circuit which grounds pin J8 of the ECU, but that was a no go. That probably just kills ignition while the ECU is still powered. If a fast break of ECU power works, Ia creative patch would be a milliseconds-off timer every X number of seconds. Theoretically barely noticeable to the rider and much better than intermittent heavy engine braking followed by a stall if the throttle is left closed, which is VERY distracting and not safe.
The bike in question is my wonderful 2019 Beta 390 RR-S, but I suspect the problem would apply across all the FI model years many model years. It is not a common problem at all and I've never seen it mentioned or detailed anywhere in the internet, and no fault code is generated.
WHAT HAPPENS
Intermittent complete loss of idle when the throttle is closed, which then of course includes the loss of the very appreciated timed ramp-down to normal high idle to reduce the problem of immediate engine braking. Once the problem starts, and I can tell immediately because there is over-aggressive engine braking, if I then leave the throttle closed and slow to a stop, the rpm will descend to a stall with the little ticks of the engine starting decompressor function kicking in. As I roll to a stop dead engine I catch a wif of over rich fuel condition, which shows the injector pulses are still active and effective, but there's not enough air to allow fuel burn. I know ignition is fine because if I crack the throttle open to give it more air the engine fires back up.
WHAT TRIGGERS THE PROBLEM
Throttle being closed after modest to hard acceleration. Maybe 1 out of 20 times. Riding around gently will not initiate the problem.
WHAT CORRECTS THE PROBLEM
Pushing through the loss of idle and loss of the timed ramp-down to idle, with some cursing, and the ECU will eventually regain a kind of equilibrium and restore to normal idle. Or just roll to a stop and cycle the key off and back on and restart. If I roll to a stop after dying and then try to start the bike without cycling the power, the bike will not want to start throttle closed, as there is loss of idle bypass air. Throttle more open will allow the bike to start, but it will be balky and over rich because the TPS tells the ECU to add fuel on top of an already over-rich situation.
WHAT IS APPARENTLY HAPPENING DURING THE PROBLEM
The idle bypass stepper motor pintle drops to close off idle air, perhaps all the way to the throttle body seat.
ANALYSIS
The ECU is the brain and the stepper motor is a slave to it. The effect of the intermittent fault manifests in the stepper, which is commanded by the ECU. The ECU makes decisions of what the tell the stepper from inputs like mass-flow sensor and TPS. A new TPS was fit, so that's not it. The Beta mechanic said he swapped to a different mass flow sensor, no change. I think he also swapped the stepper? Hmm.
DO I UNDERSTAND THE SYSTEM?
A good start, no? Check me and correct me, please.
The idle bypass air control is via a 'stepper motor' that works on motor rotation based on stepped current inputs by the ECU. A 4-wire idle bypass so there are two DC motor coils (phase A and phase B - ECU pins D3 & D4, and C4 & E4), one coil for turning the motor armature one way a certain number of step counts, and a separate coil for turning the motor armature the other way a certain number of step counts. On the end of the armature is a threaded shaft screwed into a rounded-end-cylinder-shaped thing called a 'pintle' that does not rotate. When the one motor turns the shaft one way, the pintle extends, and the other way the motor makes the pintle retract. Motor rotation and pintle extension/retraction response is super fast. There are no additional wires to provide the ECU with absolute position feedback and it can only command the pintle to move based on the number of pulses to each coil. The stepper is oriented vertically, so the thing is either more up (more idle-air bypass), or more down (less idle-air bypass). And if the thing descends all the way to touch the throttle body air-bypass seat, NO idle air bypasses the closed butterfly valve and the engine, throttle butterfly closed, will die unless pulled along by the bike, in which case is accompanied by heavy engine braking.
How does the ECU know where the pintle is so that when starting it is positioned for the correct idle? I think it does this referencing off something known. I think when you cycle the power to the ECU it commands the pintle to overshoot the seat and either the ECU knows when the pintle hits the seat by change in current or resistance, or it's just so fast the command will overshoot and dwell some milliseconds, after which idle position is simple: to a pre-determined number of opening-coil step counts, as determined by other factors, such as temperature. For example, when the engine is cold (as in not-summer type cold), the idle will run high at first, and the time to ramp down to idle will be longer. As the engine warms, the idle comes down, and the timed ramp-down shortens to the running-temperature timed ramp-down, which is a real blessing by removing the traditional FI problem of heavy engine braking when the butterfly valve is shut. Brilliant!
How exactly the system works I can only infer from how it behaves, as finding tech documentation on systems like that of the Beta is like pulling teeth. Manufacturers like to keep that behind some proprietary wall of darkness, which doesn't help diagnosis when things go wrong.
ECU 1-HOUR SWAP
If a person local to Albuquerque would please come over with their close-enough Beta 031.40.015.10.00 ECU for 2019-ish bike, for a quick ECU swap I'd REALLY appreciate it! Buying an ECU and having the dealer program it ($600?), only to retain the problem because it's NOT the ECU would just make me puke. Update: If the problem continues to persist, just bit ethe bullet and buy a new ECU and have it programmed to the bike.
SENSOR?
Not the TPS. That's new. Beta tech said he did a swap of the of the T-MAP sensor with no change in the problem. RPM sensor? Two temperature sensors? These appear to all be working.
A PATCH?
Given cycling the power on and off immediately corrects the problem, I've been eyeing a 'patch' solution of some means to manually or automatically cycle the power off in a blink to the ECU at pin A4 (like turning off the key). I tried doing that with the engine stop circuit which grounds pin J8 of the ECU, but that was a no go. That probably just kills ignition while the ECU is still powered. If a fast break of ECU power works, Ia creative patch would be a milliseconds-off timer every X number of seconds. Theoretically barely noticeable to the rider and much better than intermittent heavy engine braking followed by a stall if the throttle is left closed, which is VERY distracting and not safe.
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