I cannot figure this out! Huge power dip.

DanijelTodic

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Hey guys,

I have been trying to figure something out for a while now.

My bike really hesitates when I give it full throttle in second gear between 3900 and 4000 rpm. After 4000 it's perfect, before 3900 perfect as well. In all the other gears it takes off perfectly. The bike keeps on accelerating like it's given half throttle in stead of full until I release the throttle and start accelerating from a different rpm.

If I roll on the throttle then it's fine but if I snap it open she chokes. Now if she did this always I would blame it on not rolling on the throttle. But in all other scenarios I can snap the throttle and fly off.

The bike is a 2015 with 60.000km

I don't get it! Is this a APS, TPS thing or is it something about my flash and the ECU mapping?

Hope you guys can shed some light on this.
 

WJBertrand

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I think this is normal. Suddenly yanking the throttle open abruptly reduces intake velocity. It’ll take a while as the RPMs build before efficient velocity is restored unless you start closing the throttle again.


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DanijelTodic

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I think this is normal. Suddenly yanking the throttle open abruptly reduces intake velocity. It’ll take a while as the RPMs build before efficient velocity is restored unless you start closing the throttle again.


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I thought about something like this as well. But why does it only happen in such a specific moment? No problem in different gear or different rpm. Just second gear and 3900 - 4000 rpm.

It almost feels software related...
 

jbrown

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A flash could easily cause just about any engine performance abnormality. Without knowing what changes from stock were made, it is pretty much impossible to make any judgements. But am unusual problem that only shows up in one gear, at a particular narrow rpm range and throttle combination, on a bike where the ECU mapping has been changed would point me to the flash.
 

DanijelTodic

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A flash could easily cause just about any engine performance abnormality. Without knowing what changes from stock were made, it is pretty much impossible to make any judgements. But am unusual problem that only shows up in one gear, at a particular narrow rpm range and throttle combination, on a bike where the ECU mapping has been changed would point me to the flash.
I also can't think of anything else... Maybe TPS or APS sensors? I am going to check with the guys that did the flash if they ever heard of this before.
 

Checkswrecks

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TPS adjustment can definitely cause a flat spot like you mention, but it ought to be in all gears, not limited to one.
 

Alexander

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That's true. Then it must be the mapping
Likely. As I said in your first post on the matter, hesitation upon rapid throttle changes is almost always a fueling issue -- it's the first place I'd look, at least.

You've identified a specific load/RPM point, which will help your tuner look into it.

Suddenly yanking the throttle open abruptly reduces intake velocity.
...but pressure increases to compensate (Bernoulli's principle).

This is objectively true when viewing datalogs -- manifold absolute pressure (MAP) for most engines will be around 25~50 kPa throttle closed, and increase toward barometric 100 kPa throttle open, as engine vacuum dissipates. This is the basis for the "load" axis on speed-density VE tables, and volumetric efficiency will generally increase with load and increase with RPM (i.e., more throttle requires more fuel, more RPM requires more fuel).

I've never personally tuned a motorcycle, but I gather a lot of them use Alpha-N (TPS-based fueling) or a hybrid thereof, which has some inherent drawbacks (fueling at 40% throttle will be the same regardless of whether you're going uphill or downhill), but this is often a necessity when using multiple throttle bodies -- MAP signal doesn't provide much resolution or is otherwise too unstable for SD.

Digressing, but it's a fun topic.
 

DanijelTodic

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Update: I want to my tuner and we tried different mappings and even returned to stock. No difference. Well one big difference. I tried a new completely linear map and I loved it so we flashed that one but the hesitation in second gear is still there.

Tuner thinks that the gear sensor could be faulty and telling the ECU that it's in neutral en thereby giving it a different mapping. But I think that even with the neutral map there should be no hesitation.

Does the bike even have a dedicated gear sensor or is done through software?

This is getting to be a very mysterious problem to diagnose....
 

jbrown

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It has a neutral sensor. You could jumper the clutch switch to force the neutral map. If it's that map, then all gears would have the problem.
But the tuner can change the neutral map, too.
 

WJBertrand

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Mine does this too, both with stock ECU tuning and with Anthony’s tune. It not there rolling on the throttle in any kind of normal way. I’m not worried about it.


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DanijelTodic

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It has a neutral sensor. You could jumper the clutch switch to force the neutral map. If it's that map, then all gears would have the problem.
But the tuner can change the neutral map, too.
He thinks that the sensor is getting false readings and it only happens in 2nd gear because it's close to normal...No idea if this makes any sense. He was confused about this as well.
 

DanijelTodic

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Mine does this too, both with stock ECU tuning and with Anthony’s tune. It not there rolling on the throttle in any kind of normal way. I’m not worried about it.


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Only in 2nd gear? Or in all gears? Because my bikes pulls stronger and crisper from 3500 rpm then 4000 in second gear when I go WOT without rolling on
 

jbrown

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He thinks that the sensor is getting false readings and it only happens in 2nd gear because it's close to normal...No idea if this makes any sense. He was confused about this as well.
I understand the thought that the neutral switch could stay showing neutral when in second. My suggestion was to force the neutral map by jumpering the clutch switch as a test. If you jumper the clutch switch, then all gears would use the same neutral map, and you would see whatever effect that map causes in every gear. If the problem still presented only in 2nd gear with the clutch switch jumpered, then it is not the map.
You could probably accomplish the same test by disconnecting the neutral switch.
 

Alexander

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I believe the neutral sensor is located on the right-hand side of the engine, bolted into the engine casing from the rear. It's a pintle-style, not rotational. If your tuner suspects a problem with the switch, you could at least verify its operation with a voltmeter. Seems to me you'd be getting a neutral light on the dash if it were false triggering, though?

If you want to get really crazy, you might be able to use very thin shims to adjust the neutral switch's depth to see if it affects anything, but I've no idea if doing so would be a complete waste of time -- just going off of what the tuner said.

As jbrown is saying, it might be possible to induce the problem to see if it can be fixed. Seems to me that the high-load region on a neutral map wouldn't really be used at neutral, so the tuner should theoretically be able to command different fueling there to influence the false-triggering in 2nd gear. But take that with a grain of salt, I'm just speculating.

The entire purpose of control systems is to maintain stability, to maintain control, and it's strange to have a region of engine operation in which the fueling cannot be influenced -- a loss of control.
 
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