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Discussion Starter #1
I have read quite a bit about what seems to be a common issue. Have even posted in the past here.

I have a few questions though that maybe someone can shed some light on.

I live at 6,000 feet in elevation. While on a trip recently to the coast(sea level) the dead spot wasn't there-at all....

Now back up to where I live and it's extremely noticeable. When I hit just about 3,900 rpms and stay in that range the bike will start to lurch/hop and ride really rough. I either need to ride in a gear that is revving higher or lower and get away from the 3,900 spot.

When I accelerate, as long as I run smooth through 3,900 there is no issue. It's only when I'm riding at lower speeds and of course the bike wants to be RIGHT on 3,900, that there is an issue. Basically when riding at 40mph and lower it's somewhat of a juggling act, and frankly super annoying.

From my reading, it may seem that not much can be done. Is this just how my bike is? If I were to take it to a shop could it be something based on my altitude?
 

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I live in the Denver metro (~5000ft), and had the same problem when i first bought my bike. Now after replacing the exhaust with CF cans, chopping the airbox, chipping the bike and removing the evap canister (vacuum leak), the problem isn't entirely gone, but it is much much better.

Replacing the fuel filter also helped, as it is a fueling issue.

It has something to do with bad math in the marelli 1.6 ECU, from your experience with the change in altitude it sounds almost as if the fuel curve isn't correcting properly with altitude changes.
 

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tahoe, something can be done about that 3.9k rpm mess. ecu chips are available to help/cure this malady . had the same issue on my 2002 st2 . bought a fim 161 chip from bcm motorsports , installed, problem solved. many st 2's feature this 'lean spot' . make sure your tps, fi is setup properly before purchasing chip .
 

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Discussion Starter #4
The guy who had the bike before me installed a new chip. I haven't looked at it myself but I have the plastic box it came in and it's a ultimap um161. Website is dead, www.fuelinmoto.com.au

Not sure if that helps or not in this equation.

Lastly, what is and how do I set the TPS????
 

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not much on fi, still learning. if your bike had carbs and you ride at different altitudes the solution is to make more air available. this is usually accomplished by making large holes in the air box which have plugs or change jets. remove the air box plugs as you go up and add as you go down. i think the st2 is a closed loop system with no exhaust sensor [02 sensor] to regulate things, it acts like a carb in some ways and goes richer the higher you go. you need to do this by hand very much like a carb. just my $.02.
 

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The (now defunct) Fuelinmoto website had an excellent technical descrition of this problem which affects all Ducatis with the 1.6M and 1.5m ECUs. There is no cure, it can only be minimised by careful set up, some bikes are worse than others, some run perfectly.
Fortunately I 'd saved a copy of the very article so I will post it here.

"8 - My Guzzi/Ducati has a misfire at 3400 rpm on steady throttle - why?"

Firstly, some background on the Weber 1.6M ECU as used on 1100 Sport and 916
Biposto.

The controller is the Motorola 68HC11, a chip developed ten years ago for
injection applications. Delco ECUs also use this chip. Although it's only 8
bit it has 16 bit math, and is found in many other applications as well as
injection.

The timing is derived from one sensor at cam speed. On Ducatis this is the
cam drive jackshaft, on Guzzis it's in the cam drive in the timing chest.
The sensor collects 48 pulses plus 2 gaps (known as missing tooth
triggering) totalling 50 intervals, for a resolution of 14.4 degrees
crankshaft per pulse. The ECU derives both engine speed and phase from this
sensor. By phase I mean the point in the firing cycle of each cylinder.

Previous Ducati and Guzzi models used a processor which took 2 triggers, one
directly from the crank at 90 degree intervals, and one phase trigger which
took one pulse from the cam drive, ie once per two revs, to identify engine
phase.

Herein lies the first, and most common, problem with all of the late model
bikes. The ignition timing is derived from a half-speed sensor, which is
prone to mechanical backlash... this means that under certain engine
conditions, the gear which triggers the sensor is wobbling slightly between
drive and trail on it's driving gear. In other words, the advance is
calculated from an interval which can vary depending on mechanical slop in
the cam drive.

Two factors affect this. First, the period immediately before the relevant
ignition point is used to calculate the degrees of advance as a fraction of
the overall period of 14.4 degrees. So variance on the interval produces
variance on the fraction. Secondly the computer also calculates RPM from the
same interval. The ECU has a sophisticated acceleration / deceleration
algorithm which anticipates what is happening next, based on the history of
recent pulse intervals. If the pulse intervals are getting shorter, the ECU
assumes acceleration and modifies the ignition timing to accomodate a
predicted shorter interval in the next pulse. If the pulse intervals are
lengthening then the ECU assumes deceleration, and also trims the advance.

Now, if the interval is changing from shorter to longer, PULSE BY PULSE, the
ECU is buggered because it cannot tell if the engine is in acceleration or
deceleration. So we have a misfire situation. This is precisely the kind of
operation you mention where your engine stumbles on cruise at 3400 or 3800
rpm. As you said, the engine pulls fine on drive, but if the engine is
slopping around on constant throttle, the ECU can have difficulty working it
all out, and you get a stumble. In my opinion this stumble is a "wild card"
ignition pulse, maybe 10 or more degrees out, as the ECU tries to figure out
an engine mode. You would also observe that it only has one bad ignition
pulse usually, which often completely stops the engine. We have been
observing this phenomenon since 1995 when the 1.6 was introduced on Ducati
748SP models.

The funny thing is, the rpm point at which this happens is different from
Guzzi to Ducati, even from 1100 Sport to Daytona RS. But there's the rub,
because each engine has different bore/stroke, different resonances, and
each individual engine is microscopically different to the last. That's why
some bikes seem to runs flawlessly, and others of the same type stall at
every traffic light.

Further, the previous ECU did not exhibit this fault to any great degree.
Remember that this ECU used an RPM (and ignition) trigger which was on the
crankshaft, with no possible backlash. The only time this fault shows on the
older ECU is when the main bearings are failing, and the crankshaft is
wobbling on the bearings. This also produces a sequence of short and long
pulse, which confused the ECU in a similar fashion. This I have seen dozens
of times, with disbelieving customers who refused to listen to me when I
said their misfire was caused by failing main bearings! It proved true in
almost every case. (or crankcase, because a broken crankcase does the same thing by allowing the crankshaft to wobble in the cases).

The solution.. there is no solution yet. Again I am treated with disbelief
when I suggest that to get rid of a misfire you split your 916 engine and
re-shim the jack-shaft end float, and check the play on the jackshaft
bearings. "But it's the computer" they cry.

A final comment on this misfire problem. Both Ducati and Guzzi produced a
model which switched from the P8 ECU to the 1.6M ECU in mid-production. The
1994 916 Strada (solo seat) used a P8 ECU, and the Biposto (95 - now) uses a
1.6M. The engine spec did not change at all when they swapped to the new
ECU, but suddenly the bikes had a misfire. Some people even traded their
Stradas on a Biposto, only to find they had exactly the same power, but with
an added misfire. The same applies to the Guzzi Daytona Racing (P8, C cams)
and the Daytona RS (1.6M, C Cams).

We are still trying to find a fix for this in software, but I confess I
don't think it is really possible. The main reason it is more prevalent on
Guzzis is simply the variance in manufacture compared to Ducati."
 

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i think the st2 is a closed loop system with no exhaust sensor [02 sensor] to regulate things, it acts like a carb in some ways and goes richer the higher you go. you need to do this by hand very much like a carb. just my $.02.
It's called open loop, not closed loop. All fuel injected Ducati compensate for altitude by using an electrical barametric pressure sensor. However, the compensation is only partial. On early FI Ducati the compensation for elevation (barametric pressure) was complete but it was found that a faulty sensor would cause a potentially damaging lean condition and so later models only provide partial compensation to avoid this. I've found it to work very well on my ST4s to over 12,000 feet but it is important that your system is not too rich to begin with.
 

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Discussion Starter #9
So in short. My bike is running to spec-which means like TOTAL crap at 3,900 rpms... Great....
 

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can the bp sensor be replaced or is it bulit into the ecu? if the bp sensor was faulty and causing a lean mix at higher el's wouldn't the lean condition be amplified at sea level with more 02 available? tahoest2 states the bike ran fine at sea level.
 

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maybe you could remove the air box lid and try a short run, if it runs better then you are to rich, worse to lean. i also have to wonder why the after market chip, does your bike have any intake, engine or exhaust mods that would require a different chip?
 

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Mike is right.
In a nutshell there are 5 "inputs" to the open-feedback ECUs:
Water Temp
Air Temp
RPM
TPS
Barometric Pressure

The last 2 take a precision, "regulated" 5VDC from the ECU and give back to the ECU, something in-between 0V and 5V. The TPS, if set up correctly should be 0.150V with the butterflies totally closed (and the one TB set "free").

Then, at idle, it ends up somewhere around 0.400V +- say 50mV (milli-volts). So, you should be able to read the output of the TPS at the ECU, if you take the connector apart. The voltage reading should start at this lower voltage, (0.4nnV), and increase CLEANLY as you SLOWLY open the throttle. At WOT, it should be close to 100% of
the 5V (that is the input from the ECU). If it's shows any sign of static, or weirdness in between, the TPS is bad. (It functions like a volume control on an older radio)

Same 5V for the BP. It's up in front, on the left side, INSIDE the fairing. Has a small rubber tube coming out of it going to "nowhere" (prolly a less turbulent area).
This has an input back into the ECU that should look constant. Not sure if the "range" is zero to 5V, but it's most likely zero to "something". Baro pressure at 6000 feet is a bit less than at sea level, right? So if you force a SMALL amount of pressure into that tube (approaching sea-level), the reading should "do something". Conversely, if you suction out a SLIGHT amount of pressure (going to 15,000 feet!), the reading will go the other way. If it were my bike, this is what I'd be playing with to see if the signal going back to the ECU was clean, and repeatable.
 

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Here are some "fun facts":
http://www.tpub.com/content/engine/14105/css/14105_18.htm
"As one ascends, the atmospheric pressure decreases by approximately 1.0 psi for every 2,343 feet. However, below sea level, in excavations and depressions, atmospheric pressure increases."

So, if you do the math, at 6000 ft., you're down 2.5psi. So that's the amount you'd need to "add" to simulate sea-level. And evacuate the same 2.5psi would bring you to 12000 ft. simulation. If I were to muck with it, I think I would try a couple of feet of scrap hose, a gauge to verify, and use your mouth to puff in up to 2.5psi, and also evacuate about the same amount...see how much effort is needed to get these values.

I'm pretty sure you'll be able to produce these amounts, because I have played with vacuum gauges in the past, and it is amazing at how much vacuum you can produce...
Pressure might be a little more challenging!

Oh, about the "5 inputs"... I never mentioned the ECU's outputs: The ECU "brain" decides when to provide SPARK, and how long to hold the injectors open... So if any of the 5 inputs are amuck, or glitchy, that's how the engine is gonna run--glitchy or stumbly.
 

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Discussion Starter #14
Went for a ride today of about 125 miles. Started where I live at just about 6,200ft dropped to 4,000. From 4,000 to about 5,500 the 3,900 rpm dead spot is virtually eliminated. The lower elevation nearly it's gone entirely and up to 5,000 about the same.


for what it's worth, some data.
 

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Tahoest2: These baro sensors pop up once in a while on eBay.
I just got an email from MetroDuc ([email protected]) [I guess I signed up somehow...I see him sell used DUCs all the time--but he strips them and sells them as parts]

Anyway, he's for a 2000 996 selling for parts now. The baro sensor for it will work on an ST2, 4 probably 3. It's going for $25. Write to him and offer him $15, and see if he bites. (email in paranthesis above)
 
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