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Discussion Starter #1
I've been searching postings and have found a few about the Fat Duc. Since they were not strictly about the Fat Duc, I did not want to hijack the thread with my question.

The SF is my 3rd Duc and yes they have all had the lean, jerking, bucking, sometimes coughing/popping issues. I know it is due to the Euro 3 standards. The first 695 Monster ended up with the terms, ecu and open airbox on it for free from Ducati (because the leanness melted the paint off the engine) and it worked flawlessly. The next was a 696 that I had only for a year, so I never got around to fixing the the bump and grind of the engine.

I'm interested in getting the Fat Duc but can't get the company/individual to answer the phone or email.

I think it is an interesting take on adding more fuel to the cylinders but there is one problem (I think). So you add the Fat Duc, get it adjusted to your taste and take it for few rides. It appears that as you adjust the Fat Duc to add more fuel, the Lamda sensor's would detect the added richness and add (or subtract) more voltage. It seems you would eventually end up just where you started. I understand the concept but it appears that regardless of what you do to manipulate it, the lamda sensor is going to pick up on the richness (according to the map table) and adjust it again. Meaning that you cannot win.

Does this make sense or am I off into never, never land.

Understand that I'm not a mechanic so this is all theory in my head.
 

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Bill G has done the most tuning with the fatducs on his SF so he should be able to give you some detailed info.
Chris
 

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Bon Vivant
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Gearider your deduction makes total sense.
I know that a few very competent tuners have tried the fatduc system and have come back with poor results. Dan Kyle comes to mind.
I also know that some have had what I would call "limited" success.

I have them (streetfighter takes two) on my bike and they do improve the low end fueling issue but they do not eliminate it.

I've found that the best improvement has been with the dials turned to full rich, but I do get a "check engine" light while riding at a steady throttle.
The CEL is "lamb 6.1" which means, as you surmised, we are not fooling the o2 sensors.

I'm going to do some maintance on my bike in the next few days and I'm going to dial back the fatducks to see if I can stop
the CELs without bringing back too much of the problem fueling. I'll report back if I have anything to report

I also want to note that while I do get a CEL on nearly every ride the bike is working VERY good at this point.
 

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The fatduc takes the readings from the O2 sensor and manipulates what gets back to the ECU, tricking it into running richer. it does not actually richen the fuel, just changes the readings the ECU is getting form the lamda sensor.
 

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Discussion Starter #7
Gearider your deduction makes total sense.
I know that a few very competent tuners have tried the fatduc system and have come back with poor results. Dan Kyle comes to mind.
I also know that some have had what I would call "limited" success.

I have them (streetfighter takes two) on my bike and they do improve the low end fueling issue but they do not eliminate it.

I've found that the best improvement has been with the dials turned to full rich, but I do get a "check engine" light while riding at a steady throttle.
The CEL is "lamb 6.1" which means, as you surmised, we are not fooling the o2 sensors.

I'm going to do some maintance on my bike in the next few days and I'm going to dial back the fatducks to see if I can stop
the CELs without bringing back too much of the problem fueling. I'll report back if I have anything to report

I also want to note that while I do get a CEL on nearly every ride the bike is working VERY good at this point.
Thank you for the detailed information. I look forward to hearing of (if any) changes.

It looks like a more practical solution to our problem would be to always keep the ECU at a constant voltage below 5K. In other words, instead of trying to trick the ECU with a different voltage reading, therefore pouring more fuel into the cylinders we would block the output from the Lamda sensor and tell the ECU a lower voltage than what it required and therefore always dumping more fuel in at lower RPM's. Make sense?

If that does make sense, the question would be, how? I guess we could unplug the Lamda sensors, get a voltage feed directly from the battery, drop the voltage using a Variable Resistor from 12 to 6 or less, so we could fine tune to the optimum level of fuel mixture. Which should eliminate most problems but probably not all. The reason I say most is because I assume the map loaded in the ECU has leaner settings at some RPM's than others, that couldn't be controlled unless the Variable Resistor was actually a computer itself which could vary voltage at various RPM levels.
 

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I'm going to do some maintance on my bike in the next few days and I'm going to dial back the fatducks to see if I can stop
the CELs without bringing back too much of the problem fueling. I'll report back if I have anything to report.

Flyn, do you have a constant CEL with the Fat Ducs?...if not, at what point does the CEL go out?...please keep us informed of your findings...
 

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Bon Vivant
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sometimes it stays on, sometimes it goes out. It mostly comes on with steady throttle, if I vary the throttle I usually don't get a light.
But who wants to constantly speed up and slow down while riding in town?
 

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I really wish that somebody who knows the inner workings of the stock ECU would put out some information on it. There's a lot of unknowns when it comes to the O2 sensors and closed loop on the Ducati fuel injection system.

I've done some tuning work on early-90's stock Ford ECUs, which have a large aftermarket following and there are products available for it that allow you to get deep into the functions of the stock computer, modify it, and data log it. The oxygen sensors used on the Ford, and that you find most commonly on most automobiles, are only accurate in a very narrow range of possible fuel/air ratios - specifically 14.7:1, which is the most efficient air/fuel ratio - due to the nature of the way the sensor works (In other words, it's not a calibrated setting). Using these O2 sensors, the computer is able to tell if the engine is running richer or leaner than 14.7:1, but it's not able to tell how much richer/leaner. For example, it cannot really tell the difference between 15:1 and 17:1, or 13:1 and 11:1, but it can tell the difference between 13:1 and 15:1. You can think of the O2 sensor as working like a 2-position switch with a "lean" indication and a "rich" indication. The system operates in closed loop by commanding an increase in fuel until the O2 sensor switches to "rich", then it commands a decrease in fuel until the O2 sensor switches to "lean". These switches happen about once or twice per second and the net result out the exhaust pipe is a 14.7:1 ratio which is fuel efficient and good for emissions.

The Ford system only operates in closed loop at light/part-throttle after the engine is fully warmed up. Looking at my data logs, if you give it about 1/2 throttle or more to accelerate, it kicks into open loop, which is a little richer, to facilitate smoother acceleration. In my experience, rich AFRs, below 12:1, are associated with smooth engine operation, very smooth throttle response, slightly quieter exhaust note, no popping on decel, and slightly LESS power overall. Slightly lean AFRs (about 14:7 to 15.5:1) are associated with MORE power overall, popping on decel, jumpy throttle response, and louder exhaust. Very lean AFRs (above 15.5:1) are very uncomfortable. The engine bucks, power suffers dramatically (flat spots, etc.), the engine runs rougher, hotter, and you might even get some detonation.

Obviously the Ducati system works a little differently. We've seen stock dyno charts with low-RPM AFRs in the 16:1 + area. My assumption when I see this is that Ducati had to do some very radical things to pass possibly very misguided Euro emission regulations. Lean AFRs result in very hot exhaust gasses. Hot exhaust gasses are required to activate catalytic converters. I would hazard to guess that Ducati engineered the stock ECU to run at near dangerously lean AFRs to maximize catalyst effectiveness on start-up and at the rpm that emissions are tested.

Given what I know about oxygen sensors (as I summarized above), it would be impossible for the ECU to maintain something like a 16:1 AFR solely through closed loop with the type of O2 sensor found in the EFI systems I'm familiar with. Furthermore, all O2 sensors require a brief warm-up period (10 to 30 seconds, maybe?) before they start providing accurate information. However, I definitely experience the lean flat spot when I accelerate out of my driveway 3 seconds after a cold-startup. Putting all this together tells me that closed loop operation probably doesn't have much to do with why the bikes run lean at low rpm. I think it's programmed in the open loop fuel tables, and I don't think the bike runs a true closed loop system that you find in most conventional EFI systems.

Of course I have to acknowledge that Ducati may be using wide-band O2 sensors, which can accurately sense a wide range of AFRs, to obtain the lean-running low-rpm conditions. But these have historically been prone to inaccurate signals as they age.

Hopefully this helps explain how the Fatducs are supposed to work. If you intercept the signal from the O2 sensor to the ECU, you can lie to the ECU and tell it that it's always running leaner than it is, causing the ECU to command more fuel. However, the ECU doesn't blindly follow what the O2 sensors tell it. In the Ford system, the computer monitors the number of lean/rich "switches" it's getting from the O2 sensors. If they are too slow or stop, it throws a CEL. This may be the same type of thing that the Ducati ECU is doing to throw a CEL. If this happened in the Ford computer, it would start ignoring the O2 sensors and just run off of the open loop fuel tables. If you agree that the low-rpm lean AFRs are probably programmed into the open loop tables on the bike, this explains why people are having mixed results with the Fatducs.

But who knows for sure?! I don't, and that's why I've got my credit card at the ready the moment Microtec or Nemesis makes an ECU with traction control available...
 

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Discussion Starter #11
sometimes it stays on, sometimes it goes out. It mostly comes on with steady throttle, if I vary the throttle I usually don't get a light.
But who wants to constantly speed up and slow down while riding in town?
Someone else mentioned that these are twins and will not act the same as 4's, I agree but I don't think that is what we are after here. We are simply asking for a smoother ride on the low end of the RPM.

Before I got my ECU flashed, I almost dropped the bike a couple of times at slow speed due to the abrupt throttle response right after that bad lean spot. I think it was around 3750, if I remember correctly.

Too fast to ride at legal speeds and doesn't like to run slow, hmm. I guess we could move to Germany :)
 

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sometimes it stays on, sometimes it goes out. It mostly comes on with steady throttle, if I vary the throttle I usually don't get a light.
But who wants to constantly speed up and slow down while riding in town?
Glad you're having some success with the Fat Ducs. I had forgotten about them and was about ready to give up on ever getting my stock bike to run right.

I had hoped that a ProTune stock map would do the trick, but Matt at MotoWheels told me that I would see only a slight improvement throughout the rev band.
 

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Bon Vivant
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Someone else mentioned that these are twins and will not act the same as 4's
This is total Bullshit. You can check any AFR from a dyno run of a stock SF.
They do not meter fuel and timing properly from the factory - end of story!
Get the AFR right and the bike will be smooth as silk.
 

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One more question...the adjusters on the fat Duc don't look all that precise, how confident are you that you're getting the same amount of fuel to both cylinders?
 

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Bon Vivant
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One more question...the adjusters on the fat Duc don't look all that precise, how confident are you that you're getting the same amount of fuel to both cylinders?
you can't, the fatducs are a total gamble.
Infact I believe this was the problem that Dan Kyle had when he put a bike on a dyno with them,
he was unable to get consistent readings or make reliable changes.
It's a poor workaround but what else do we have without spending a grand or better?
All I can say is its improving the way my bike runs
 

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Discussion Starter #16 (Edited)
This is total Bullshit. You can check any AFR from a dyno run of a stock SF.
They do not meter fuel and timing properly from the factory - end of story!
Get the AFR right and the bike will be smooth as silk.
That's not what I meant by that comment. For me owning a inline 4 and twin are completely different even if the fuel is setup perfect. Meaning that twins are not glass smooth, they shake a bit, they have personality. I equate inline 4's to flying. They are so smooth and quiet (factory exhaust) that I fill like I'm literally flying because the feed back from the engine is almost none existent at constant throttle.

I'm on my 4th twin now (yes one was a HD Low Rider) and can't see myself ever venturing back to an inline 4.
 

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My bike throws the CEL intermittently and the dealer has not been able to get it to do the same. The fatducs and ecu are probably having an argument between themselves every now and then, much as zach34 has alluded to.
I think it is pretty poor that there has been no other moves from the factory to alleviate the problem. Much like the deforming plastic gas tank issue many other Ducati owners are having......... if the factory has done nothing about that issue, which is 10 times bigger than our fueling issue, then we have little hope for help. I will certainly be keeping this in mind in future when considering another purchase.
 

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before I did the protune and PCV I had the fatducs on and they didn't do too much to improve the stumbling on the SF. I didn't have them cranked all the way up though.
 

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Bon Vivant
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That's not what I meant by that comment.
And what I meant was there is a difference between a motor that has some inherent vibration and one that vibrates because it doesn't run properly.

I'm not a V-twin snob, I personally feel plenty of feedback from an I4 and I don't believe a v-twin has a
soul (as some would suggest) because its cantankerous. For my taste the only V twins worth owning are the
performance oriented overhead cam engines that can run at a higher RPM, the rest are just crappy running truck engines.
 

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And what I meant was there is a difference between a motor that has some inherent vibration and one that vibrates because it doesn't run properly.

I'm not a V-twin snob, I personally feel plenty of feedback from an I4 and I don't believe a v-twin has a
soul (as some would suggest) because its cantankerous. For my taste the only V twins worth owning are the
performance oriented overhead cam engines that can run at a higher RPM, the rest are just crappy running truck engines.
Hey now, let's not knock my Ultra Classic :D :crazy:
 
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