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It could...remember the old car radio volume knobs (and Yamaha receivers)? They would develop some wear/corrosion or something that interfered with the electrical signal at a point or two. But you should also look for vacuum leaks around the throttle bodies too. Another thing that we've noticed happening is a small ring of crud that builds up around the throttle body where the butterfly meets the side wall (presumably from the crappy EtOH laden gas we're forced to use). This can leave you with some erratic performance at very low throttle openings. You can remedy that easily by spraying a rag with carb cleaner and wiping out the inside of the TB.
 

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Hi all,

I haven't seen this mentioned, but found it to be an unexpected cure for a similar rideability symptom (slight stumble, rough running under 3000 rpm). On my 2000 ST2, I replaced the air sensor (552.4.002.1A Pressure sensor) found under the front left upper fairing.

The bike had always run a bit rough under 3K. I just chocked it up to a big twin wanting to run at a higher RPM. But the problem became noticably worse at high altitudes while on a trip from Virginia to Wyoming. In fact on a couple of Wyoming mountain passes, it almost became unrideable. Also, the symptoms extended up into the 4000 - 5000 range but would clear above 5K. Once back in the comfortable 1000 to 2000 ft elevations of the Blue Ridge Mountains, the bike returned to normal I replaced the air pressure sensor anyway, feeling guilty I had not addressed that frustrating problem from my trip.

After replacing the sensor, the original rough running below 3000 completely disappeared. The bike was a totally different machine at those speeds. In fact, for several rides I ran at 2000-3000 or so the whole time. I didn't lug it, having heard of potential crank shaft failures when loading the bike at low RPM. But I did short shift and cruise at those RPMs when possible (which was pretty often). The bike was silky smooth. Unbelievable. Added a whole new dimension to the bike's demeanor.

Might be worth a look. I paid about US $35 on eBay for a used one and got lucky.

r-

Tom C.
 

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Discussion Starter #23
Hi all,

I haven't seen this mentioned, but found it to be an unexpected cure for a similar rideability symptom (slight stumble, rough running under 3000 rpm). On my 2000 ST2, I replaced the air sensor (552.4.002.1A Pressure sensor) found under the front left upper fairing.

The bike had always run a bit rough under 3K. I just chocked it up to a big twin wanting to run at a higher RPM. But the problem became noticably worse at high altitudes while on a trip from Virginia to Wyoming. In fact on a couple of Wyoming mountain passes, it almost became unrideable. Also, the symptoms extended up into the 4000 - 5000 range but would clear above 5K. Once back in the comfortable 1000 to 2000 ft elevations of the Blue Ridge Mountains, the bike returned to normal I replaced the air pressure sensor anyway, feeling guilty I had not addressed that frustrating problem from my trip.

After replacing the sensor, the original rough running below 3000 completely disappeared. The bike was a totally different machine at those speeds. In fact, for several rides I ran at 2000-3000 or so the whole time. I didn't lug it, having heard of potential crank shaft failures when loading the bike at low RPM. But I did short shift and cruise at those RPMs when possible (which was pretty often). The bike was silky smooth. Unbelievable. Added a whole new dimension to the bike's demeanor.

Might be worth a look. I paid about US $35 on eBay for a used one and got lucky.

r-

Tom C.
Hello Tom, I am hopeful that your suggestion just may be the trick! I can truly imagine how you felt once this type of problem was finally solved. I know how I will feel once I have achieved the same result. Thank you for this suggestion!
 

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Discussion Starter #24
Well, I researched about finding a replacement air pressure (some say atmospheric) sensor for my 2004 ST3. Alas, it doesn't look like Ducati put one on the ST3. It's not on the parts list and I couldn't find one anywhere except on eBay where some ads said that the ST2/ST4 model worked with an ST3. It could be just marketing.

If anyone on the forum can confirm that the ST3 does have one please let me know.
 

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The ST3 uses an atmospheric sensor that is integral to the instrument housing. It isn't a separate sensor that can be replaced.
 

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Although...the service manual references an "air temperature/pressure sensor as well as the atmospheric pressure sensor in the dash.

Edit...further reading of the manual states this is an air temp sensor only...chalk it up to translation issues.
 

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LJ - I guess I figured these machines all had some sort of air pressure or mass sensor. Sorry for the Wild Duc Chase.

r-

Tom C.
 

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st3 should be nice and smooth down the bottom. saying they don't run right down low just confounds me.

do you have other options for someone to look at it? getting a definitive answer on closing springs, etc.
 

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Discussion Starter #31
st3 should be nice and smooth down the bottom. saying they don't run right down low just confounds me.

do you have other options for someone to look at it? getting a definitive answer on closing springs, etc.
I agree! Ducati makes a excellent motorcycle and I cannot believe that this is normal. My options to take it to another mechanic are limited. There are two dealers about 45-50 miles away. One says that their Ducati mechanic is out indefinitely due to the Covid-19 thing, something that I don't understand. I called the other and was told that my ST3 is so old that they aren't sure that they will work on it and said that they would think about it and call me if they would. They never did. The next dealer is in San Francisco, 2.5 hours away. In San Francisco there is also DesmotoSport, a really good independent and I have appointment there is about ten days. That's a tough one as I would rather not have to drive down there and back to leave it and then do it again to pick it up.

I am focused on the TPS right now and plan to explore that area this week. It really feels like a fuel mapping issue at minimal throttle and a TPS issue sounds like to likely place to cause such a unusual symptom.
 

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The way I test TPS is back-probe connector output (paper clips work well if you don't have proper probes), ignition on engine off. Use multimeter between sensor output and earth and very slowly turn throttle. What you are looking for is smooth voltage increase. A old school analog multimeter works best but can be done with digital in a pinch.Also note that the readings are earth referenced via the ECU so might be worth checking as well.
 

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Discussion Starter #34
Thanks, Turbmart for your suggestion. Do you know which of the three leads on the TPS is the earth ground?
 

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Couldn't tell you without consulting the wiring diagram but it's pretty easy to figure. Unplug sensor, ignition on, check voltages on plug. One should be 5v supply, other two will be near zero. Next check continuity to ground to establish which is the earth and the one left is signal.
 

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Discussion Starter #36
Couldn't tell you without consulting the wiring diagram but it's pretty easy to figure. Unplug sensor, ignition on, check voltages on plug. One should be 5v supply, other two will be near zero. Next check continuity to ground to establish which is the earth and the one left is signal.
I checked the service manual schematic and it looks like the ground is the left pin that connects to the black/violet wire with the middle pin that goes to the ECU connecting to the brown/green wire. I will verify this and report back once we test the TPS.
 

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just backprobe the wires with the ignition on. one will be about 5v, another about 0v and the third ranging from 0.4v to 4.8v depending on throttle opening.
 

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Got my ST3s in 2012 with low kms/miles ..... the full DP kit had been installed by dealer , confirmed .... first few rides similar issues with rough running popping under 3000rpm .... bought shop manual ,did some reading , then did a full service , still a bit rough , looked at pipes DB killers still there , removed them , all fantastic since , bike runs smoothly way down low no rough running , better fuel distance , only occasional popping on downshifts ..... really haven’t thought on it since until reading this thread .... good luck sorting it !
 

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Discussion Starter #39
Using an oscilloscope we tested the TPS and it tested clean, no noise with a steady climb to 5 volts as the throttle was opened. Another component eliminated. I was getting to the point that of replacing the remaining components to see if it helps cure the stubble. Then yesterday, I received the 2004 copy of Rider magazine that had a full road test of the ST3 and was surprised to read that the reviewers experienced very similar symptoms on a new US model. They expressed surprise as they didn't experience that on the ST3 that they road during the release test in Barcelona, speculating that it could be due to US emission requirements. It made me wonder if they might be something might be different about that bike. Could it have been a EU version? What would be the difference? The ECU! I was shopping for a used US ECU on eBay for testing purposes and found a seller that had one, plus the same part number only with a EU sticker. I ended up buying it for $91.

Now for the $64 question, can I use this ECU without modification on my 2004 ST3? I have read one post on the forum that stated that once a ECU had been "red keyed" it could no longer be used on a different bike. Is this true? I also read that it is possible to have an ECU reset to factory specs at some shops. If this is necessary, does anyone know where this could be done? It would really be cool if this ends my long struggle to make this Ducati run properly like my previous ones.
 

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if it is an oem fitment ecu then it will be coded. you need to get the ecu virginised or disable the immo function. then it will work in your bike.

there were a couple of eu ecu, the early and the valve spring update. they both probably have the same 035 number on them, but the software number will be different. there's at least 3 different versions of the 035 file.
 
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