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:
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!
- 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!