Snatchy Throttle - Technical Explanation
Here is the snatchy throttle (don't get confused with other issues like surging at cruise, dips in the power band and so on):
With a stock GSXS (certainly on my 2019 F model) I have mapped what happens to the fueling on my dyno.
Up to 2,500 rpm, if you shut the throttle there is no fuel cut off when the throttle is closed.
After 2,500 rpm and up to about 7,000 rpm, once you close the throttle (completely 100% closed), the ECU software will activate a 100% fuel cut off AFTER 1.5 seconds. If you get back on the throttle before the 1.5 seconds, then there is no snatch (snatch is caused by fuel coming back in with a bang - like you turned the ignition back on). If you missed the 1.5 second time slot, you cannot avoid the snatch. HOWEVER, if you allow the bike to coast back down to 2,500, the fuel will start again EVEN at 100% closed throttle. Thus avoiding the snatch.
Above 7,000, if you close the throttle 100%, there will still be fuel flowing, but if you allow the rpm to drop to the 7,000 mark, then after 1.5 seconds the fuel will be cut again.
And here is it in a video. You will notice, when he cuts the throttle, that the AFR shoots up to 18. If his gauge went up higher, you would see it shoot up to 50 plus (ie no fuel at all, just fresh air).
If your bike to does not suffer from this then either:
You are riding below 2,500 rpm OR not opening the throttle again until 2,500 rpm is reached on deceleration OR
You are opening the throttle before the 1.5 seconds has elapsed, thus avoiding the cut off from activating (there is a YouTube vid out there of a guy showing how the snatch has been eliminated after fitting a PCV but you will notice he always gets back on the throttle before the 1.5 seconds has elapsed!). See it here:
OR
You are riding in the upper rpm range (above 7,000 rpm) where the fuel cut off does not operate OR
You are just so used to riding a poorly set up bike that you have now adapted to it and have compensated by feathering the clutch when reopening the throttle, or you have taken up so much slack in the throttle cables, that the fuel cut off does not activate because the cable tension does not allow the throttle to close completely (throttle needs to be 100% closed for the fuel cut off to activate) or you do as I did in the Picos in Spain recently, you adopt a riding style that never shuts the throttle 100%, so never let go of the throttle, just get it back to 1% or 2% and hold it there (tricky to do without a DynoJet Pod-300 that displays your throttle position at all times) but it can be done.
You MIGHT, I say MIGHT (as I have no proof yet that this works) be able to fool the ECU into thinking the throttle is at 1% (and therefore not at 0% and therefore not activating the deceleration fuel cut off and the snatch) when you let go of it and it closes, if you adjust the TPS to a position where it effectively tells the ECU it is still open when it isn't. This would stop the deceleration fuel cut off from activating, as it only comes on with 0% throttle opening. I haven't been able to mimic this with the Power Commander software (which allows you to adjust throttle position on the software) but you may be able to do this by experimenting with various TPS positions on the sensor to find one that stops the fuel cut off from activating.
It may even be that the 1.13 volts position will do this (fool the ECU into thinking the throttle is still open by 1%). It may explain why some people report that a fiddle on their TPS fixes their snatchy throttle and for others, it doesn't work. As some have already said, finding a voltmeter that gives you a true 1.13 volts and tightening up that bolt is not going to be very accurate. Neither is using the old model method of the -C00 thing. Basically, it will be hit and miss IF this actually does stop the deceleration fuel cut off from activating - the jury is out on that one.
Yes, the only fix for THIS niggly problem, is to deactivate the deceleration fuel cut of by using the Woolich Racing mapping software.
Now, all you guys that have had your ECU "mapped", how many know for certain, that this function has been switched off?
I do not believe you could ever override the deceleration fuel cut off by simply re-mapping the fuel maps, or using a PCV for adjusting the piggy back fuel maps (I haven't been able to achieve this with my PCV and a dyno).
"Mapping" covers a multitude of things, which fall into 2 categories; ECU functions and maps. Changing the fuel or ignition maps will not stop the deceleration fuel cut off from operating and causing the snatch. Only deactivating this function using the Woolich Software (or others - if there are others?) will stop it from happening. In fact, I might even suggest that by simply deactivating this function alone, it will transform the bike. I have the software on order and will test this out by deactivating this function and running the bike (mine is stock everything) with the original OEM map.
Suzuki, even with the revised fueling on the new (new from 2017?) ECU, were unable to stop the snatch. They would have been breaking the law if they did. Remember what happened to VW? Even dealers would be unwilling to make this change, even if they have the equipment to do it. And as they have proved, it cannot be cured with new fueling maps.
Once I have sorted this out with my Woolich Software, I will take a look at the lean cruising issue (surging and so on). If you look at the Superbike article on the DynoJet remap of the bike, you will see that the lean running at low throttle positions is the cause of this. What we have yet to determine is why the subsequent DynoJet map takes fuel AWAY at these throttle openings in an attempt to fix the issue. Makes no sense to me. We shall see.
With a stock GSXS (certainly on my 2019 F model) I have mapped what happens to the fueling on my dyno.
Up to 2,500 rpm, if you shut the throttle there is no fuel cut off when the throttle is closed.
After 2,500 rpm and up to about 7,000 rpm, once you close the throttle (completely 100% closed), the ECU software will activate a 100% fuel cut off AFTER 1.5 seconds. If you get back on the throttle before the 1.5 seconds, then there is no snatch (snatch is caused by fuel coming back in with a bang - like you turned the ignition back on). If you missed the 1.5 second time slot, you cannot avoid the snatch. HOWEVER, if you allow the bike to coast back down to 2,500, the fuel will start again EVEN at 100% closed throttle. Thus avoiding the snatch.
Above 7,000, if you close the throttle 100%, there will still be fuel flowing, but if you allow the rpm to drop to the 7,000 mark, then after 1.5 seconds the fuel will be cut again.
And here is it in a video. You will notice, when he cuts the throttle, that the AFR shoots up to 18. If his gauge went up higher, you would see it shoot up to 50 plus (ie no fuel at all, just fresh air).
If your bike to does not suffer from this then either:
You are riding below 2,500 rpm OR not opening the throttle again until 2,500 rpm is reached on deceleration OR
You are opening the throttle before the 1.5 seconds has elapsed, thus avoiding the cut off from activating (there is a YouTube vid out there of a guy showing how the snatch has been eliminated after fitting a PCV but you will notice he always gets back on the throttle before the 1.5 seconds has elapsed!). See it here:
OR
You are riding in the upper rpm range (above 7,000 rpm) where the fuel cut off does not operate OR
You are just so used to riding a poorly set up bike that you have now adapted to it and have compensated by feathering the clutch when reopening the throttle, or you have taken up so much slack in the throttle cables, that the fuel cut off does not activate because the cable tension does not allow the throttle to close completely (throttle needs to be 100% closed for the fuel cut off to activate) or you do as I did in the Picos in Spain recently, you adopt a riding style that never shuts the throttle 100%, so never let go of the throttle, just get it back to 1% or 2% and hold it there (tricky to do without a DynoJet Pod-300 that displays your throttle position at all times) but it can be done.
You MIGHT, I say MIGHT (as I have no proof yet that this works) be able to fool the ECU into thinking the throttle is at 1% (and therefore not at 0% and therefore not activating the deceleration fuel cut off and the snatch) when you let go of it and it closes, if you adjust the TPS to a position where it effectively tells the ECU it is still open when it isn't. This would stop the deceleration fuel cut off from activating, as it only comes on with 0% throttle opening. I haven't been able to mimic this with the Power Commander software (which allows you to adjust throttle position on the software) but you may be able to do this by experimenting with various TPS positions on the sensor to find one that stops the fuel cut off from activating.
It may even be that the 1.13 volts position will do this (fool the ECU into thinking the throttle is still open by 1%). It may explain why some people report that a fiddle on their TPS fixes their snatchy throttle and for others, it doesn't work. As some have already said, finding a voltmeter that gives you a true 1.13 volts and tightening up that bolt is not going to be very accurate. Neither is using the old model method of the -C00 thing. Basically, it will be hit and miss IF this actually does stop the deceleration fuel cut off from activating - the jury is out on that one.
Yes, the only fix for THIS niggly problem, is to deactivate the deceleration fuel cut of by using the Woolich Racing mapping software.
Now, all you guys that have had your ECU "mapped", how many know for certain, that this function has been switched off?
I do not believe you could ever override the deceleration fuel cut off by simply re-mapping the fuel maps, or using a PCV for adjusting the piggy back fuel maps (I haven't been able to achieve this with my PCV and a dyno).
"Mapping" covers a multitude of things, which fall into 2 categories; ECU functions and maps. Changing the fuel or ignition maps will not stop the deceleration fuel cut off from operating and causing the snatch. Only deactivating this function using the Woolich Software (or others - if there are others?) will stop it from happening. In fact, I might even suggest that by simply deactivating this function alone, it will transform the bike. I have the software on order and will test this out by deactivating this function and running the bike (mine is stock everything) with the original OEM map.
Suzuki, even with the revised fueling on the new (new from 2017?) ECU, were unable to stop the snatch. They would have been breaking the law if they did. Remember what happened to VW? Even dealers would be unwilling to make this change, even if they have the equipment to do it. And as they have proved, it cannot be cured with new fueling maps.
Once I have sorted this out with my Woolich Software, I will take a look at the lean cruising issue (surging and so on). If you look at the Superbike article on the DynoJet remap of the bike, you will see that the lean running at low throttle positions is the cause of this. What we have yet to determine is why the subsequent DynoJet map takes fuel AWAY at these throttle openings in an attempt to fix the issue. Makes no sense to me. We shall see.
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