Beta 390 RR-S Fuel Injection Issue - A 'Little Thing' with a High-Level Solution

[Motobene]

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, and a separate coil for turning the motor armature the other way. On the end of the armature is a threaded shaft is screwed into a rounded-end-cylinder-shaped thing called a pintle that cannot 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 response is very fast, so the pintle movement is also very fast. There are no additional wires to provide the ECU with absolute position feedback and it can only command the pintle to move bases on the number of pulses to each coil. On the bike 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.

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 go past the seat and somehow knows when the pintle hits the seat. Maybe the the ECU can sense a current rise when that happens, shuts off closing, then step counts the pintle up to open the bypass to a pre determined position.

Is this actually how the system works? Beyond the base settings, the ECU can 'learn' the tweak idle rpm from the rpm meter sensor connected to the coil wire. Knowing how the system works is helpful to problem diagnosis.

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.

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.

A PATCH?
Given cycling the power on and off corrects the problem, I've been eyeing a 'patch' solution cycles power off in a blink to the ECO 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, I could get creative on a solution to do that manually or even automatically.

 

[SandRdr]

Is it going into limp mode?

 

[Motobene]

Doh! I forgot to keep the DEF tank topped up!

 

[FLrider]

When was the last time that the spark plugs were renewed? Sometimes these issues come from ignition issues rather then fueling probs.

I just watched a vid whereby a dealer wanted to exchange an automatic transmission in a GM truck and the independent mechanic found that the 8 spark plugs were worn out when he ran a diagnostic on the misfiring that was happening...... In other words sometimes it may pay to look elsewhere... YMMV...
Even a new spark plug can be bad out of the box... DAMHIK...

 

[Ridefreak]

I know the tech said the tps was ok but to me it sounds like it's going through a tps fault when your situation happens, possibly the ecu is loosing it's signal for a second. Again speculation but similar issues can be caused by the TPS circuit opening up randomly. Some TPSs are Hall effect type and use a magnetic field, the other, more typical ones use a wiper that rubs a winding and aren't quite as reliable. TPS issues are rare but if that wiper has a bad spot (likely near the idle position where it spends most of it's life at), and it looses the electrical connection for even a very short period it could cause the ecu to cycle or fault and your interrupting it's power forces a reset. Since it's intermittent, when the tech checked it the problem might not have been apparent and it's likely he would have passed right on to the next thing. Random electrical issues are always very difficult to diagnose or confirm w/o swapping out the part and riding it for awhile so the tech might not discover that. Obviously a new ECU to test would be ideal but that's unlikely. I hate easter-egging parts, swapping with a known good one is fine but buying electrical parts not knowing if it's the problem is the very last resort so I'd try to recreate the problem by interrupting the tps signal and see if the bike reacts the same, it's a long shot but it looks like you're at that point and best of all it costs nothing. IMO adding a circuit to interrupt the ecu power to deal with this situation is a hack, I get why you're doing it but it's still a hack and those often have other unforeseen consequences, I would be reluctant to ride far from the truck in our desert with that mod.

Good luck!

 

[slomo]

I'm curios to know if your low idle issue occurs when you ride at different elevations (compared to where you live or normally ride)?
If so, have you tried the stepper motor reset procedure before you ride?

It's also unclear if your mechanic checked the stepper motor via their laptop diagnostics or replaced it with a new one?
It's worth cleaning the stepper motor and the cavity it lives in to see if it clears up your issue (free and simple test), or replacing the stepper motor as an additional test to see if it is the issue.

While it's possible the ECU is faulty, the probability is extremely low.
The majority of time, a sensor providing input to the ECU is bad, or a mechanism the ECU is controlling is bad.
So unless your buddy down the street has an ECU to swap out as a test, I would look at those other things first.

Good luck and let us know your progress.
FWIW - Beta USA stands by their bikes and will work with the dealer to resolve the issue.

 

[Motobene]

I just landed on the other side of the world on 24h no sleep. My Beta problem seems far away, and in a way it is.

I do appreciate all the feedback. My attention span is demented at the moment, so I'll take some time on replies.

 

[Motobene]

FLrider, the spark plug is not the issue. The bike is like a new machine in all its details.

TPS, almost certainly not it. The problem was present with the new TPS, made and bought long after the original TPS was made.

Ridefreak, the problem isn't low idle. It's instant no idle. Stepper motor resets? I've done SO MANY of those! For years I blamed not doing those right or not enough. Resets never eliminated the problem.

The stepper was checked via diagnostics, and it's been a while and I can't remember if he swapped the stepper. I think yes. He definitely swapped the T-MAP.

I do think 'easter egging' is in order for all the sensors.

 

[Ridefreak]

When I answered I didn't even realize Beta uses an idle stepper motor, nor that you swapped the TPS. Those steppers gave issues on some Tigers also, I wouldn't care for that method's complexity on a offroad bike but I understand why some do it that way.

Unfortunately it often takes a special manufacturer's system to exercise and test something like an idle stepper motor and if the problem is intermittent then it's doubly hard. I've run up against similar issues and I've used more indepth methods then are typically available to the avg guy figuring this out in their garage. I picked up a small o-scope, obviously being familiar with using one for troubleshooting helps and often all it will tell you is: A. the signal is dropping out, of B. The signal changes at the time the error occurs. The ecu is still a black box from our perspective unless it's throwing codes and you can read them. If it were mine I'd look a the stepper signal with the hopes of seeing it drop out or distort when the bike dies indicating the issue is coming from the ecu or one of the ECU inputs and eliminating the stepper motor assy.

This pic is scoping the crank pressure sensor signal on a 300 TPI. The peaks are BDC and the valley's are TDC, the repeating pattern is the 2Ts 2 unique strokes. In this example I was comparing the sensor signal to the CCP pressure reported by OBD reader.

 

[Motobene]

Ridefreak, your more extensive FI experience and diagnostic tools are beyond what I know and the tools I have. I'd be more than happy to ride the Beta over to your place to o-scope the event. Can your o-scope capture and record the above-described event?

Monitoring the stepper's close-direction coil while riding would be help further define effect, and maybe help with the cause.

I can't remember if the mechanic-tech swapped the stepper. I will ask.

If not, a squeaky new $tepper is an option. However, the stepper to me is more egg than chicken, but I lack the tools and experience to instrument that.

A related step forward was finding the following video. It helped me understand how the Beta might be homing its 4-wire stepper:


At ~4:00, the fellow describes commanded 'homing steps' as more than needed to seat the pintle and shut off idle air. The overshoot simply times out, then the ECU counts steps in the other direction to the idle position. The problem is like homing to seat the pintle but without the pintle returning to its idle position, but without the pintle then rising back up for idle air. What could command this but the ECU?

 

[Ridefreak]

You've probably looked at this video. It's not very informative but he tells you when (and what to listen for) as the stepped cycles during a untouched warmup as part of it's initialization. The other thing he mentions that you may have already done is remove the stepper and clean the plunger and surrounding area.

 

[Motobene]

Ridefreak, your attached video was among the first I viewed last year when I set out to solve the mystery problem. Given sudden loss of idle, idle control via the air bypass was the first focus. Second focus was connectors. Despite every one being stuffed with silicone at setup. No change.

Then it was many hours on YouTube chasing symptoms and hoping for deeper tech understanding of Euromoto FI. That has proved over time elusive, very piecemeal, and generally fragmented lower-level info.

I did not expect dirt in and around the steeper to be an issue, as I am very particular about disallowing dirt and fine grit into the intake. Cleaning the stepper was nevertheless my first move and I did it well. I found only some surface scum on the throttle body seat and pintle, dispatched that with carburetor cleaner. I oiled what I thought might be the stepper threads, because lubricated is better than dry.

I just realized now I should pull the stepper and watch it at key on. That would teach about how fast the mechanism is, and I expect homing to happen right at key on. There should be a fast extension, then retraction to the idle position. Without actually seeing it happen, it's just theory.

Until the recent video on the 4-wire GM stepper used to FI a VW Bug, I thought maybe the ECU was sensing pintle contacting seat by current change on the closing coil, but now I see that is more simple... just a command to over run the number of required steps to contact the seat.

Stepper percent was checked at the dealer and was fine. Gosh I had done so many resets over two years by the time it went to a dealer the first time. Never seemed to do much. By visit 1, the idle had gone low and the problem was more frequent, about 8X per riding hour. TPS was not right at first visit so it got replaced. Everything was hard reset through the laptop. Hard reset at second dealer visit with component swaps from an on-dealer floor 500. After second visit the bike was running REALLY well. Test ride had problem 2X per hour, but I did not pursue then a third visit.

Tech at dealer just said that if I bring it in again that we could try an ECU swap. I'm hoping to go deeper and maybe solve this first on my own, with help from my friends

Midnight in London. Off to bed.

 

[ZoomerP]

Maybe I missed it, but have you confirmed that the ECU is getting accurate, consistent temp data?

From what you described in the opening post, the engine seems to be performing similar to what happens when a choke is closed on a warm, carbureted engine; too rich and too little air at idle results in a stall. Rolling the throttle allows more air into the system and prevents a stall. Bad temp data into the ECU could possibly create your result. Just a thought.

 

[Motobene]

Zoomer, it's not sudden enrichment (fuel), it's immediate and radical loss of idle air with no departure from normal injector pulse width.

Accelerate > close butterfly valve & TPS > [unknown fault] > fast pintle drop to seat or very near seat > hard engine braking > stall > cycle ECU power > immediate return to normal running through multiple closings and openings of throttle > repeat....