A couple of interesting points are the feature occurs during high rpm, zero throttle (chopping the throttle) and is temp sensitive (only happens whe nthe bike is hot). This seems to be a universal feature on modern FI vehicles. It just happens to be poorly implemented on our bikes.

One article I found describes Deceleration Fuel Cutoff thusly:

The fuel cut-off during deceleration is of the adapted type. When the throttle is closed and the r.p.m. exceeds 1,700 (for engine speeds lower than 1,700 r.p.m., the cut-off function is not operative in order that an optimal drive-ability can be maintained) the injection of fuel is disactivated. If the supply is interrupted, the r.p.m. will start to fall more or less quickly in relation to vehicle conditions. Before reaching idle speed, the dynamics of the fall in r.p.m. is checked. If this exceeds a certain value, the fuel supply system is partially reactivated on the basis of a logic which envisages the "soft accompaniment" of the engine at idle speed. When this condition has been reached, the normal functions at idle speed are reactivated and cut-out during deceleration will only be reactivated if the fuel cut-off threshold is exceeded to prevent the engine from jerking. The reactivation thresholds for the fuel supply and cut-off vary in relation to engine temperature. Another fuel cut-off logic has been developed within the control unit which intervenes during partial deceleration, ie. when a lower engine load is requested. The function is only activated if the new conditions last for a set period of time and after the ignition angle has been adapted to the new situation.

 

I found the bike is a lot more choppy if I don't let the fuel pump prime all the way before starting the engine. I always wait a few seconds before starting the bike after it finishes. As mentioned above, if you chop the throttle shut expect the bike to jerk. Down shift, blip, decelerate.

 

it happens in low rpms in 2nd and first... dont have a problem with it in any other gears cus if im above 2nd then i still have tons of room to stay in high rpms

hard to cruise around in stop and go traffic at 20mph @ 10krpm though

 

TheCunningMan, I am going to add your post to the other links that I have in the "Suzuki Recall" thread, good job.

 

A couple of interesting points are the feature occurs during high rpm, zero throttle (chopping the throttle) and is temp sensitive (only happens whe nthe bike is hot). This seems to be a universal feature on modern FI vehicles. It just happens to be poorly implemented on our bikes.

One article I found describes Deceleration Fuel Cutoff thusly:

The fuel cut-off during deceleration is of the adapted type. When the throttle is closed and the r.p.m. exceeds 1,700 (for engine speeds lower than 1,700 r.p.m., the cut-off function is not operative in order that an optimal drive-ability can be maintained) the injection of fuel is disactivated. If the supply is interrupted, the r.p.m. will start to fall more or less quickly in relation to vehicle conditions. Before reaching idle speed, the dynamics of the fall in r.p.m. is checked. If this exceeds a certain value, the fuel supply system is partially reactivated on the basis of a logic which envisages the "soft accompaniment" of the engine at idle speed. When this condition has been reached, the normal functions at idle speed are reactivated and cut-out during deceleration will only be reactivated if the fuel cut-off threshold is exceeded to prevent the engine from jerking. The reactivation thresholds for the fuel supply and cut-off vary in relation to engine temperature. Another fuel cut-off logic has been developed within the control unit which intervenes during partial deceleration, ie. when a lower engine load is requested. The function is only activated if the new conditions last for a set period of time and after the ignition angle has been adapted to the new situation.

Dude, that is totally it. That discribes it as good as it gets. I felt as though it was in the fuel delivery and the fact that you're at such a low RPM for these high rev motors. Now, is there a way of curing it? To allow for smoother deceleration or a maintained delivery of fuel during low RPM/pre-engine break?

Great work, I think we're onto something. I'll be stopping in to Karn's Performance this week. I'll bring this up with Jason and see what his thoughts are on it. I'm also hoping to recreate the problem prior to meeting with him. He's a very knowledgeable tuner.

 

bumping this

did anyone have a solution to this problem?
i recently bought an 04 600 and i noticed this exact same problem

 

^Deceleration fuel cutoff can be disabled flashing the ECU. I don't know about pre K6 600/750 models though. My bike has K8 1000 ECU and I have it disabled, one friend has this done to his K4 1000 and another friend is currently testing this on a K6 600.

After a quick test ride, the throttle response felt much smoother. Might need a new trip to a dyno to make fine adjustments...

fuel cut activated

fuel cut disabled

 

Hey JK750, how did you disable the decel fuel cut? I have a K6 750 running a woolich logbox, but I can't see any means to disable fuel cut.

The only thing I've come across to make a difference is to adjust the TPS to read a bit higher. So currently with throttle completely closed my TPS reads 2.8% This works for the most part, not perfectly though & I'd rather have the TPS set at the correct position.

I (& I'm guessing many others) would be extremely grateful if you could please share how you disabled it.

 

Why the spike at 40 seconds? Seems odd as it looks like it's fixed for the rest of it.

The first graph the motor was given a little more revs. But overall looks like it works.

I've done it on my bike differently by tricking the IAP sensor. The power transition is liquid smooth when you start getting into thrashing territory, backing off and coming back on throttle mid corner.

 

LogBox stopped logging before I hit the highway. It does that sometimes. I bought a new memory card, hope that solves the problem. :dissapointed

That spike is a gear change using a quickshifter. It was only +2'C and it might need mapping changes now with fuel cut disabled.

 

From the fuel maps of K5 GSXR1000s that have been floating around since the time their ECU was hacked, I seem to remember that the fuel is never cut off. Both the Alpha-N and Speed-Density maps had non-zero values for zero throttle and, what's more, these values go up smoothly with no abrupt changes as the throttle goes up.

Of course the situation might be different for other bikes, but I don't think that's very probable. I therefore doubt that the jerkyness is caused by fuel cut-off.

Having said that, I do think that the TPS is somehow responsible for the jerky throttle as it was set too low on mine and the throttle response was improved markedly when I set it as per manual. (Note here that you must not set the TPS with the engine cold or not running, as in both cases the fast-idle cam is pulling the throttle open at idle. If you set it then to the "correct" position, it will actually be set too low.)

Another theory is that the jerky throttle is caused by ignition timing, which the TRE is supposed to fix. I can only talk about my own experience on a 750K4 where I recently built and tested a TRE. It certainly decreased engine breaking at low rpms and closed throttle but it didn't do much for the throttle response as most people claim. I tried it on for a couple of weeks to get used to it and then removed it, after which I felt no change, or perhaps even a slight improvement in throttle response.

Of course, the situation might be entirely different on other machines, but I now believe that those who say there's a "night and day difference" between TRE and stock, probably have the TPS set wrong and the TRE somehow compensates for that.

 

dpapavas, so you are suggesting your opinions and hypotheticals carry a lot more weight than emperical evidence?

This suggests to me that you have no background or basic understanding of sciences or engineering at an advanced high school level.

The proof is in the graph above you. I also data logged an O2 sensor on my K7 750 and can confirm the same results as -JK750-. That is on engine over run the AFR goes as high as 22:1.

I built a circuit that prevents the IAP sensor from ever going below idle manifold vacuum and it solved the jerkiness problem on engine over run.

What is more likely is the ECM software is written so to cause a lean condition on over run, high manifold vacuum. -JK750- claims that they can flash the ECM to remove this also, but he hasn't identified what the code is actually doing.

 

What is more likely is the ECM software is written so to cause a lean condition on over run, high manifold vacuum. -JK750- claims that they can flash the ECM to remove this also, but he hasn't identified what the code is actually doing.

Somewhere in the code are some rpm limits where the fuel cut activates when you go off throttle. There are different ways to disable this.

I have flashed my K8 1000 ecu and my friend's K6 600 ecu with modified bin files.

 

Is it just rpm limits or is it manifold vacuum as well?

I understand the fuel cut wasn't on the K1/2 1K.

It has to be more that just rpm as we know the fuel doesn't cut when the throttle is open. So it may be TPS AND manifold vacuum for eg.

I still notice a spot around 4200 rpm at slow and low throttle openings that's always been there. It may be related to the SET valve or my tune being out a little. But otherwise my 750 is liquid smooth on over run to on throttle transition. It's also flaming out of the exhaust more on over run so it's definitely getting more fuel. Before it would just blow the odd blue flame.

 

I'm not the one who did the coding. So I don't know the specifics. It's there and now it's disabled, that's enough for me. Disabling decleration fuel cut completely removed herky jerky throttle.

 

Sorry dpapavas if my post come over as arrogant and condescending. I guess it was.

I was just very surprised by you comments, since the real world observations through actual measuring of the AFR (emperical evidence) directly contradicted the conclusions you were drawing from the map tables.

There is more going on with the software inside the ECM than just the map tables that have been found through reverse engineering the ECM software. Not all of the software is understood yet by the hacking guys. The source code is only available to the software engineers at Denso and AFAIK no one has ever seen it. That's what makes finding out how it all works difficult and time consuming.

I'll try to be more polite in future :cheers

 

Sorry dpapavas if my post come over as arrogant and condescending. I guess it was.

I was just very surprised by you comments, since the real world observations through actual measuring of the AFR (emperical evidence) directly contradicted the conclusions you were drawing from the map tables.

I may indeed not have worded it correctly, but I'm all in favor of empirical data, measurements and arguments built on top such data (and theory of course). I have no reason to dispute the validity of the diagrams, but one still has to explain how it can cause shock loads in the transmission.

The diagrams, as far as I understand them, do not disagree with my initial post. In fact they show that the stock ECU does not cut off fuel (as that would lead to infinite AFR). Instead, the mixture is leaned out in accordance to the fuel maps I remember, where the fuel coefficients gradually drop as the TPS value drops but stay non-zero for zero throttle. This agrees with the steep rise during throttle close and the plateaus of constant AFR when the throttle stays closed.

In any case, what I was saying is, that it is not at all clear, to me, that you can attribute jerks to a smooth 30% increase in AFR when the throttle is closed anyway. There is nothing discontinuous there, nothing that would cause a shock. The AFR rises about as fast as the TPS drops. In other words: as you close the throttle you deprive the engine of air and its power production drops significantly. The AFR rise makes it drops still a bit more. Why attribute it to that and not to just closing the throttle?

On the other hand the jerk might be attributable to just the very steep rise in AFR, even though it happens after the throttle is already fully closed. It's certainly not unthinkable, I'm just not so sure.

Finally regarding empirical data: As I said I'm all in favor of experiments and I do not doubt that people who had their ECU reflashed noticed that their throttle was smoothed out. But I have no way of knowing what the ECU tune entailed. The graphs certainly show that the AFR on closed throttle was changed, but other parameters might have been changed too. Spark advance or seconday throttle maps might also have been tuned for instance, which might well come into play as far as jerkiness is concerned. Scientific methods generally require that you single out the factors and only change one at a time. It is very hard to be sure of that outside the laboratory and perhaps that's one reason why our arguments rarely result in something conclusive.

In any case, I appreciate your apology and do apologize in turn if my initial post implied to someone that I question the honesty of what anyone said, or the data they posted, or anything like that. I guess there's nothing more to add here.

 

I didn't see it as a question of honesty, only a contradiction to the real world (empirical) data. After reading your second post along with the first I understand more what you are pointing out.

However, there are a couple of things that don't gel.

You say the "AFR rises about as fast as the TPS drops". To me there seems to be a delay going lean on TPS closed looking at -JK750-'s graphs. However that's not the issue, it's the opening of the throttle (TPS) and the lag or jerk experienced. From the graphs I'm seeing close to a 300ms delay. O2 sensors are pretty slow and close to 100ms could be attributed to the sensor itself, then there is the response time of the signal conditioning circuitry for the O2 sensor. I guess there would only have to be a 100ms delay in AFR to cause a noticeable jerk. So making sense of the jerkiness from the graphs may be very difficult. What is obvious is it goes to 20~22:1 on overrun and this raises the question of it possibly being the culprit.

The TPS is a known culprit and an incorrectly set TPS at ₋C0 will cause a huge lag or jerkiness. This had been reported by many people. By setting the TPS to ⁻C0 instead of ‑C0 at idle definitely improves the throttle transition but still doesn't cure the lag completely.

As I said previously, I have designed an electronic circuit that conditions the IAP signal to never drop below idle manifold vacuum. This has cured the lag or jerkiness completely and the throttle transition is liquid or turbine smooth. The exhaust does crackle a lot more now on deceleration and pumps yellow flames out of the exhaust.

Of interest is the K1/2 1000 does not seem to suffer this issue and I have been informed that this model did not go lean on engine overrun. I'm rebuilding my 1000 to go back on the road soon and will put an AFR monitor / data logger on it and have a look at what it is doing.

With the IAP circuit on my 750 there is still a slight lag around 3,600 rpm. That has always been there and I don't think is related to this issue as it is only at a very narrow window of revs and not consistently there. It could be a funky sensor and may not likely be a design issue. Bottom line is, as soon as I start getting into thrashing territory my 750 is so easy to control on throttle transition and is liquid smooth on off throttle even mid corner. I can back off and on again at will mid corner fully cranked and committed with 100% confidence and no upsetting of line.

I thought I was having myself on at the huge improvements made, since I designed the circuit myslef. So I took the IAP circuit off. The difference was night and day. Back to its ugly jerky self again. It's on the bike permanently now.

 

However, there are a couple of things that don't gel.

You say the "AFR rises about as fast as the TPS drops". To me there seems to be a delay going lean on TPS closed looking at -JK750-'s graphs. However that's not the issue, it's the opening of the throttle (TPS) and the lag or jerk experienced. From the graphs I'm seeing close to a 300ms delay. O2 sensors are pretty slow and close to 100ms could be attributed to the sensor itself, then there is the response time of the signal conditioning circuitry for the O2 sensor. I guess there would only have to be a 100ms delay in AFR to cause a noticeable jerk. So making sense of the jerkiness from the graphs may be very difficult. What is obvious is it goes to 20~22:1 on overrun and this raises the question of it possibly being the culprit.

There's definitely a delay (couldn't be otherwise unless the ECU could somehow anticipate that the throttle will be closed), but I was talking about rate. Even this though is not really true. The time it takes for the AFR to rise/fall is, on the whole, comparable to the time it takes to open/close the throttle, but the AFR starts rising relatively slowly and then shoots up on close and the reverse on open.

On throttle close this is probably not a problem, as the AFR transition happens once the throttle is closed and the engine is is not making any power anyway. (I recently tried shutting down the engine while engine-braking at low speed and noticed no jerk at all.) On throttle open, the rapid AFR fall happens once you've cracked the throttle open, so it may be able to account for the jerk, but that depends on the effects of AFR on power.

I couldn't find any hard data on how much AFR affects power. I have the vague notion, that AFRs within the usable range, that is, AFRs that don't cause knocking, excessive emissions or other problems, generally don't affect power "too much". I'm thinking along the lines of: say at 4-5000 rpm my engine is making about 40-50HP and also say at 10% throttle I get 10% of that (which is not true generally as the geometry of the butterfly-type throttle doesn't provide a linear plate angle to volumetric efficiency curve; it should be in the ballpark though and perhaps even a bit too optimistic), so I'm making about 4-5HP. If an AFR of 19-20 would make for a 20% change in engine power with respect ot an AFR of 15, that'd be a change of about 1HP. That power change would be delivered in a very short time, but would it be enough to cause a jerk? Perhaps so.

Initially I attributed the excessive jerkyness of my GSXR to a combination of a miscalibrated TPS and an actual fuel cut-off. I theorized that a TPS set too low would cause the ECU to think that the throttle plate is still entirely closed even when it has started to open. When the ECU perceived the throttle as starting to open, it would already be open some way. If before that, fuel had been cut off entirely and is now added again abruptly with a somewhat open throttle, I imagined that could cause the jolt. I'm not sure if that goes a longer way to explain things than the above situation though (and fuel is not cut off entirely anyway so it doesn't matter).

There's another thing to consider here. In my experience, jerks don't necessarily happen when cracking the throttle open, they generally happen when then engine goes from braking the bike to accelerating it. Under high engine speed for instance, it might take quite a bit throttle for this to happen (as much as it takes to coast at that speed). From the curves, we can see that the changes in AFR take place when the engine is still in overrun and the rpms are dropping. It takes quite a bit more throttle for the torque flow to reverse and the rpms to start climbing again. At this point though, the AFR is, more or less, stable.

From experience, I'd expect the jerk to happen at this later time, when the AFR has been smoothed out. Of course, if you open the throttle more suddenly the AFR discontinuities might coincide with engine torque reversal and then AFR enters the picture again. It is quite possible.

In general I think that the major reason for jerks is gear backlash in the drivetrain and chain slack. Whatever the ECU does to aggravate the problem must, I think, happen withing that time-frame when the drivetrain reverses torque and needs to take up the slack and the engine is essentially unloaded. This makes for some pretty tight timing...

The TPS is a known culprit and an incorrectly set TPS at ₋C0 will cause a huge lag or jerkiness. This had been reported by many people. By setting the TPS to ⁻C0 instead of ‑C0 at idle definitely improves the throttle transition but still doesn't cure the lag completely.

Yes, I've also said that in my initial post. In my case though, the initial setting was low, probably because someone adjusted it with the engine off. Once I set it in the middle the throttle smoothed out considerably. I had been trying for months to develop a smooth throttle technique before, with no results whatsoever. Now I almost never get jerks any more. So there is something going on here for sure.

As I said previously, I have designed an electronic circuit that conditions the IAP signal to never drop below idle manifold vacuum. This has cured the lag or jerkiness completely and the throttle transition is liquid or turbine smooth. The exhaust does crackle a lot more now on deceleration and pumps yellow flames out of the exhaust.

[...]

I thought I was having myself on at the huge improvements made, since I designed the circuit myslef. So I took the IAP circuit off. The difference was night and day. Back to its ugly jerky self again. It's on the bike permanently now.

I don't know what else the IAP signal might control within the ECU, but this certainly does seem to support the AFR theory of jerkyness.

 

I have recently returned to riding after many, many years break. Purchases a Suzuki GSX650F 2008 (12 months ago). From the beginning I have had a problem and have spent quite a bit of $$$'s trying to fix. Taken it to 2 places (Holeshot) and Colemans Suzuki (Auckland). I have been told that it is my riding not the bike however in desperation to find the fault I lent the bike to a member of a motorcycle club I belong to (an engineer). The bike did it for him and he has explained that it is a known problem - herky-jerky-throttle. I looked it up and it is definitely this problem.
I am not that mechanically minded though I have been able to follow the guest of this. My problem is this; what do I say to Coleman's Suzuki and what evidence can I take into them.
Any help would be most appreciated.

 

They won't have any clue what you are talking about. The guys that work at dealers are mechanics, not engineers.

What is going on here is that a lot of modern FI systems are designed to cut fuel on engine over run. It's in the software and the ECU hacking guys are the experts in that area. The professionals, the software engineers at the the ECU manufacturers really know what is going on, but that information is not released publicly. So you are left with the ECU hacking guys that are reverse engineering the software and trying to find out how it all works.

Adjust the TPS setting to how I said in my previous post and see if that improves it. I.e a little on the high side of the bar being in the centre.

 

Here is a brief explanation about this, it's for a Yamaha but same thing with a Suzuki. Flash Forward | Sport Rider

"The R6’s stock ECU turns the injectors off when the throttle is closed and revs are above 10,000 rpm (first and second gear) or 5,000 rpm (gears three through six). If you dip below the threshold rpm or open the throttle 1 percent, the injectors begin firing again, but if you’re in the middle of a corner, that transition from injector off to injector on can upset the chassis—or you. FT ECU’s solution is to immobilize the R6’s Injector Decel Cut function (read: leave the injectors on always). Although fuel mileage will definitely be affected, Gardell says there are multiple benefits to leaving the injectors on: “Keeping the injectors turned on makes a little difference with engine braking, but more than that it helps when you go to get back on the throttle. It’s to stop that initial hit because the injectors are completely off with the stock ECU and there’s no strategy to ramp it back in. It’s just like a light switch,” Gardell says. “Now, even if you’re at 8,000 rpm in third gear and off throttle, where you don’t necessarily need to be burning gas, it’s still going to fire the injectors because the transition going back onto the throttle is going to be smoother.”"

One way to disable this is to raise those rpm limits above bike's normal rev limit.

 

Hi guys, sorry for revive this post and for the poorly english,

1 year ago I had a gsxr 1000 2009 where I could disable the fuel cut through the whoolich racing software, now I have a gsxr 1000 2005, that i dont know that its possible disables the same decel fuel cut, my question is, in the gsxr 1000 2005 the ecu have this option or in this model de fuel cut is active?

 

Yes, you can disable it also on a K5-K6 1000 but not with Woolich.

 

Yep, I read that list of options, and I believe that you say "they don't update the site" , I write again today told them that I cant see in the list that option, and they answered this:

Dear G20VTR

The option is in the software file. I checked before I answered

 

Little update and for information,

After installing the hardware today and connect to the ECU, the option "disable deceleration cut off" is available. 👍🏻