Dangerous Decel Fuel Cut

[ia02]

I am having a horrible fuel cut / AFR spike issue on gentle throttle off - throttle movements that I am in desperate need of help with. The bike is a 2017 model with the following mods:

• PCV
  • rev xtend to 11,200 rev limit
  • auto tune active on closed loop section (0%-60%, 0-7,500 rpm) - 13.5 AFR target
  • dyno tuned on open loop section
• WB2 - set up by Hard Racing - set to 13.5 AFR
• Tyga header
• Akra slip on
• Open airbox
• K+N filter
• Gray Area KTM larger fuel injector (350cc)

It is most specifically occurring between 9,500 rpm and 10,500 rpm when rolling off and then back on the throttle in the 20%-60% partial throttle range. We are able to replicate the issue on the dyno and have graphed it. The issues is only happening when rolling on and off the throttle. On steady acceleration, AFR stays acceptable when accelerating through the "problem cells" but spikes super lean and then super rich if we feather the throttle in those cells. Even the smallest roll on to roll off causes the issue. When riding it feels like the throttle has turned into a full on or full off switch. It can not be tuned out with timing or with fuel adjustments, we have tried extensively. Below is a photo of exactly what is happening.



As you can see in this replication scenario we are accelerating from 8,000 rpm to 10,250 rpm at approximately 40% steady throttle. AFR is more or less steady in the acceleration part (yes I know AFR is fluctuating a bit, but not excessively). We then roll off from 40% throttle to 20% throttle, the AFR spikes to 18.0. When we roll back on throttle to 30%, the AFR plummets to 10.0. Roll back off to 20% and the AFR spikes to 18.0 again. For those of you who have tuned a PCV on a 2017+ model you will recall that 10-40% throttle positions are VERY VERY close together. Even the smoothest rider will easily jump between these values. The throttle is much less sensitive in the 60-80% range. This all leads us to believe the fuel is being cut for some reason, perhaps by the stock ECU?

Again, when we accelerate from essentially idle to the rev limit in any throttle position the AFR remains solid. When we accelerate across throttle positions the AFR is solid. This issue only occurs during the most minute roll off to roll on situations. It makes it IMPOSSIBLE to ride smoothly in the sweet spot of the power curve in corners. I am afraid this will result in a race crash so I am forced to ride around it but short shifting to a higher gear or just slowing down substantially in the corner. This bike is only track ridden and is raced.

Other things we believe we know: The throttle and TPS appear to be working properly. As you can see in the graph, only the AFR is spiking...the throttle position and corresponding RPM changes are very smooth. The bike has no other symptoms. It pulls hard and runs very smooth in all other situations.

Here is a link to a video of a replication from a dyno session yesterday.

https://www.dropbox.com/s/mzsd9xu6rlpmd2q/2019-08-13 16.37.46.mov?dl=0

So, questions:

Has anyone experienced this?
Does anyone know specifically if a decel fuel cut is a feature in the stock ECU?
Could the PCV or WB2 be causing this?
Is there another piggyback tuner or standalone ECU that is known to NOT have this horrible issue?
Any other ideas on how to further diagnose or isolate?

I am hoping the experts will chime in here. I would prefer to not post separate topics in the vendor sections. THANKS IN ADVANCE EVERYONE!

 

[chevaliernoir]

My bike is 2015, so complete different fuel system.
BUT, I also complain about the behavior in corners.
Even if I dont have fuel cut off, my way to solve it is to decrease spark advance in such condition, and at a little bit higher TPS. The effect is a loss of torque that you compensate with higher TPS. Then maybe you will be out of the fuel cut off area.
In your case I would also wonder why you are so rich before the fuell cut off occurs. I would check and correct manually the pcv Calibration in this point.

I wrote a long message about my engine tuning, also with records here if interested here https://www.rc390-forum.com/forum/k...orum/3192-ready-race-machine-4.html#post31290

Using pcv with data recorder I found that in dynamic condition, the correction does not always appear when we want. For example, :
- rpm is measured during one engine cycle,
- then, in best case, the fuel correction is applied at next engine cycle,
- then the combustion occurs at the following engine cycle,
- then the O2 sensor can evaluate the result.
But at that point, the rpm is not anymore the same as in the beginning, so the new correction may be applied at the wrong rpm.
From your record, I feel you have this issue : because the system see the high richness, it removes fuell, but not at the correct rpm/TPS, and this increase the ON/OFF behavior, and you have a divergent control... I imagine you can find this if you look at auto-tune Map.

 

[chevaliernoir]

My bike is 2015, so complete different fuel system.
BUT, I also complain about the behavior in corners.
Even if I dont have fuel cut off, my way to solve it is to decrease spark advance in such condition, and at a little bit higher TPS. The effect is a loss of torque that you compensate with higher TPS. Then maybe you will be out of the fuel cut off area.
In your case I would also wonder why you are so rich before the fuell cut off occurs. I would check and correct manually the pcv Calibration in this point.

I wrote a long message about my engine tuning, also with records here if interested here https://www.rc390-forum.com/forum/k...orum/3192-ready-race-machine-4.html#post31290

Using pcv with data recorder I found that in dynamic condition, the correction does not always appear when we want. For example, :
- rpm is measured during one engine cycle,
- then, in best case, the fuel correction is applied at next engine cycle,
- then the combustion occurs at the following engine cycle,
- then the O2 sensor can evaluate the result.
But at that point, the rpm is not anymore the same as in the beginning, so the new correction may be applied at the wrong rpm.
From your record, I feel you have this issue : because the system see the high richness, it removes fuell, but not at the correct rpm/TPS, and this increase the ON/OFF behavior, and you have a divergent control... I imagine you can find this if you look at auto-tune Map.

 

[ia02]

My bike is 2015, so complete different fuell system.
BUT, I also complain about the behavior in corners.
Even if I dont have fuell cut off, my way to solve it is to decrease spark advance in such condition and at a little bit higher TPS. The effect is a loss of torque that you compensate with higher TPS. Then maybe you will be out of the fuell cut off area. In your case I would also wo der why you are so rich before the fuell cut offoccurs. I would check and correct manually the pcv Cali ration o. This point.
I wrote a long message about my engine tuning, also with records here if interested here https://www.rc390-forum.com/forum/k...orum/3192-ready-race-machine-4.html#post31290
Using pcv with data recorder I found that in dynamic condition, the correction does not always appear when we want. For example, rpm is measured during one engine cycle, then in best case the fuell correction is applied at next engine cycle, then the combustion occurs at the following engine cycle, then the O2 sensor can evaluate the result. But at that point, the rpm is not anymore the same as in the beginning, so the new correction may be applied at the wrong rpm.
From your record, I feel you have this issue : because the system see the fuell cut off, it add fuel, but not exactly at the correct rpm, and you have a divergent control... I imagine you can find this if you look at auto-tune Map.

I could be wrong but I don’t think we are having the same issue. My open loop map is not auto tuned. Furthermore, I don’t believe (but again could be wrong) auto tune makes any on the fly fueling corrections. It only gather suggested trims needed to accomplish the target AFR. The map has to be manually updated with the suggested trims before changes to fueling are made.

 

[chevaliernoir]

You're right, at 9.5k / 10.5k rpm you're probably not in closed loop control (do you know what is the closed loop control area on your bike?) and I understand you do not use autotune, so it is not an issue of control.
May you share your map? I really think you should first try to avoid the richness excess that happen before the fuel cutoff?
If you come back to a richness of ~14.5 for TPS 20%/40% you will loose torque. You will compensate by increasing the grip position, and you may gey out of fuel cut off area controlled by Bosch ECU.
Decreasing the ignition advance will also act in the same way.
Don't be afraid to decrease torque at intermediate TPS. This is usually unvisible for the rider as we compensate by opening higher TPS value.

Keep us informed. I'm interested.