Idle screw, ST3 2004 - Ducati.ms - The Ultimate Ducati Forum
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post #1 of 11 (permalink) Old Aug 31st, 2019, 8:05 am Thread Starter
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Idle screw, ST3 2004

Hi all,
I have a question for the resident nerds here please.

I was asked the following question:
Quote:
Doesn't your Duke have a stepper motor and use the W5AM controller and interpretive TPS Dan?
Then I was told this:
Quote:
I really don't know whether Ducati use a similar set up.[to a Guzzi] They do use the same ECU though and I *Thought* that they also used an air over idle system. Now it won't be identical and may in fact be completely different but on all the systems I am familiar with that use the W5AM apart from the Bellagio the idle speed is coded into the ECU and it then uses a stepper motor to control the idle.

This means that as long as it is tuned correctly if the engine speed drops the stepper allows in more air, this leans out the mixture ao the idle speed increases. If the revs rise? The inverse is true, the stepper closes and the mixture richens up dropping the idle.

The thing is that for the right amount of fuel to be added, not just at idle but throughout the entire throttle operation the ECU HAS to know how much air is being flowed. On Guzzis, and I believe Ducatis from your period, there is no MAP, (Manifold Air Pressure.) or MAF, (Mass Air Flow.) sensors. The way the ECU judges how much air is being flowed depends entirely on the interpretation of the throttle plate angle supplied by the TPS, (Throttle Position Sensor.).

Now that is established at the factory by a boffin in a white coat on a flow bench and the TPS is not physically adjustable. It's signal is interpreted by the ECU based on algorithms built into interactive tables in the 'Map'.

The problem is if you then fuck with the throttle stop screw you change the amount of air being flowed BUT the ECU doesn't know that because it is built and mapped to assume that only 'X' amount of air is being flowed and now it's flowing X (+/-N) where N is an unknown.

While you can turn the stop screw to a degree without changing the idle speed, (Because the stepper motor will change the mixture to try and maintain the ECU's programmed 'Target Idle' as soon as you are off idle the AFR's, (Air/Fuel Ratios) are completely fucked up! The wider the throttle opening the less it matters but since we all ride around in the 1/4 to 2/3rds throttle position most of the time it's this area where the damage and poor running will be most manifest.

Now it may be that Ducati got Magnetti Marelli to design a different system for them, although I think it unlikely, but I do strongly suggest you find out, and not just by asking 'A Mate', exactly what system they do use before you go randomly fiddling with screws on a fuel injection system because that way lies madness, pain and financial punishment of 'Old Testament' type proportions!
I would appreciate if any of you could clear this up for me. I was recently advised by a local Ducati shop that to raise my idle I could simply adjust the idle stop screw, which I did, and it no longer stalls at the lights and seems a lot smoother at very low speed. But I have no idea if I have fundamentally changed the tune by doing this simple adjustment. I know I turned it a full turn to get it to idle at 1000rpm.
Thanks.

2004 ST3
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post #2 of 11 (permalink) Old Aug 31st, 2019, 8:43 am
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2004 st3 has no idle control valve, and has a non linear tps. base line set up is here: BikeBoy.org - Ducati 4V Desmoquattro Non Linear TPS Baseline Adjustment (plus ST3)

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post #3 of 11 (permalink) Old Aug 31st, 2019, 7:05 pm Thread Starter
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Thanks very much. From my understanding of that tutorial the vertical idle screw activates on the fast idle setup? Is that right?
I also see that under no circumstances will I plug my diag tool into this bike without an expert standing next to me to teach me.
Cheers.

2004 ST3
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post #4 of 11 (permalink) Old Aug 31st, 2019, 7:59 pm
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the st3 won't have a vertical idle screw. the fast idle is part of the cable wheel. #13.

you use the diag tool to read the throttle angle.

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post #5 of 11 (permalink) Old Aug 31st, 2019, 11:22 pm Thread Starter
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Quote:
Originally Posted by belter View Post
the st3 won't have a vertical idle screw. the fast idle is part of the cable wheel. #13.

you use the diag tool to read the throttle angle.
Mine has this vertical screw that is a throttle stop.

2004 ST3
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post #6 of 11 (permalink) Old Aug 31st, 2019, 11:40 pm
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that's the horizontal.

red injectors. that's wacky.

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post #7 of 11 (permalink) Old Sep 1st, 2019, 3:11 am Thread Starter
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Ah, so horizontal refers to the front cylinder rather than the actual alignment of the screw?
And you're saying my bike is wacky? Not to me it ain't.

But the bottom line here is that I can use that screw to up the idle without stuffing the tune of the bike right? Or not??? It's what my local Duke bloke said to do.

2004 ST3
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post #8 of 11 (permalink) Old Sep 1st, 2019, 4:56 am
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not, but if you didn't read that line i guess do whatever you want.

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post #9 of 11 (permalink) Old Sep 1st, 2019, 6:10 am Thread Starter
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Bugger! I had an inkling this was the case. What effects am I likely to see? Excessive fuel consumption I spose. It seems to go better but who knows? I should find someone who could have a proper look at it. Is there anyone in the Northern Rivers or Southern Queensland who does this stuff? I'm not at all confident to mess with it myself.

2004 ST3
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post #10 of 11 (permalink) Old Sep 11th, 2019, 6:40 am Thread Starter
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Left in the dark here guys. I contacted another place that specializes in Dukes and they recommended twisting the throttle body screws which I have to assume is that one on the linkage.
It fixed the problem as far as I could see, but I just wanted to make sure I wasn't buggering the tuning and now I've had two shops tell me it's OK to do that, while Belter seems intent on putting the fear of Dog into me if I touch anything.

Another opinion would be good.

2004 ST3
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