What is the purpose of the stepper motor on breva/norge?

[rodekyll]

I'm trying to understand the throttle control on the 2v 1200 breva/norge.  What does the stepper motor do?  I know what one is (computer drives have them).  I just don't know how it relates to the bike.

[Matteo]

It keeps the idle up when you start, cuts out when it's warm.

[rodekyll]

So it's the electrical equivalent of the high idle lever on my EV?

[ohiorider]

David,  the diagram in the Guzzi manual makes it look more  like a linear actuator.  The actuator is used to open or close air passages modifying the air/fuel mixture at idle to maintain the proper idle rpm.  It doesn't physically move the throttle plate(s), but controls idle via providing a richer or leaner idle mixture.  Sorry I'm not on my desktop ..... I have drawings from the manual that show specifically how it works.  Soon as Time Warner and I figure out why my download and upload are so slow, I'll send them to you.  In the meantime, maybe someone else can send info to you.

Bob

[Vasco DG]

Sort of, but it also operates to compensate for changes in air pressure, temperature etc.

There is a target idle speed programmed into the ECU. If it detects the idle speed is dropping to low it will open the stepper valve, leaning the mixture and raising the idle. If the idle speed rises the it closes the valve to enrichen the mix and slow things down.

The thing is that the ECU assumes how much air is being passed at idle through the throttle butterflies. They are set up on a flow bench. (reasonably accurately!) so whenever the TB's are balanced the ECU starts off with a baseline *Knowledge* of how much air is passing through them and then extrapolates from there as the butterflies open.

This is the reason why the air bleeds should only be used to set the idle balance after the high speed balance has been achieved. If both bleeds are open it can allow too much *Extra* air in and the stepper can't cope and will keep overcompensating one way or the other so the engine 'surges'at idle and low throttle openings.

This is the reason why the idle stop screws should never be messed with on the W5AM equipped bikes. Do that and the amount of air passed changes but the ECU can't know that, so it all goes 'Udders Skywards' very fast.

Pete

[rodekyll]

So if I'm absorbing this in the proper dose -- this stepper controls the idle at ALL engine temperatures, not just cold running?  And it's a necessary feature of the W5AM?

[Vasco DG]

Not absolutely necessary, various folks who've had idle problems have stuck a  'turn off' valve in tne stepper line 2ith vavarying degrees of success. IMHO though it is better to find the root auwe of problems if you an rather than simply circumventing them.

Pete

[beetle]

Not a necessary feature of the 5AM as such, but the 5AM's  application by Guzzi, because there is no MAF sensor.

[rodekyll]

We're talking theory here.

What if we didn't use the 5AM?  What if we used the dirt-simple 15M and plumbed the 15M harness into the engine?  It looks to me like all the sensors are the same and the critical components have the same plugs, so the physical hookup looks possible.   If I used the center-pivot throttle struts/linkage from the early y2k bikes and the older-school handlebar-mounted high idle lever, could I simplify things?  We're assuming we can do whatever we want to here . . .

[beetle]

What about keeping the 5AM and using a modified bin/map from a Bellagio? The Bellagio has no stepper. Simply add your fast idle linkage and throw in a map built using the Bellagio map as a base. No stepper control in the software.

[molly]

The stepper is only useful when cold starting on my 1200 2v motor. I switch it off after 30 seconds and have no exhaust popping as a result.

[Vasco DG]

What about keeping the 5AM and using a modified bin/map from a Bellagio? The Bellagio has no stepper. Simply add your fast idle linkage and throw in a map built using the Bellagio map as a base. No stepper control in the software.

As you know, this is not my area of expertise but that suggestion would seem to make sense as the Ballagio essentially uses the 'Cali' TB system but engine management is controlled by the W5AM.

David, if you want to experiment we can easily flick you a Bella map for you to start playing with.

Pete

[molly]

In a ideal world that is what I would do but to add a fast idle linkage would be a pain far easier to fit a tap in the stepper motor/ airbox pipe. Some people don't bother with a tap even they just block off the pipe and apply a bit of throttle for the first 30 seconds or so.

Edit:Wouldn't a friction cruise control do the same job as a fast idle lever?
http://www.demon-tweeks.co.uk/Product.do?method=view&n=345&p=175386&c=215&utm_source=Google&utm_medium=Base&utm_campaign=Handlebar%20Accessories&gclid=CLD6v6aE7sQCFWzHtAodKR4Azg

[pauldaytona]

The previous generation bikes have an air bypass in the throttle body, with a screw to set the amount. That controls air when the throttle is closed. That does not exist in 5am controled thottle bodys. Because the stepper valve air circuit does do that function. So yes you con mount a 15m, and get a new dash too. But also need and old fashioned throttle body too. So why? with decent map a 5am bike runs great in all circumstances.

[Kev m]

FWIW the steeper motor or IAC (Idle Air Control) Valve was the standard method used to control idle speed in all conditions for the automotive industry from about the time EFI became commonplace until electronic throttles made it obsolete.

I've always been told that its purpose was strictly to allow the ECM to add air to speed up idle to the desired level over some purposely low base setting (base position of the throttle plate).

I've never heard before that it would specifically be used to change mixture too.

Maybe it does and I've always thought about it too linearly.

But if you think about it the ECM has a much better way of doing that (injector pulse width) so why would the designers make it more complicated?

[rodekyll]

In a ideal world that is what I would do but to add a fast idle linkage would be a pain far easier to fit a tap in the stepper motor/ airbox pipe. Some people don't bother with a tap even they just block off the pipe and apply a bit of throttle for the first 30 seconds or so.

Edit:Wouldn't a friction cruise control do the same job as a fast idle lever?
http://www.demon-tweeks.co.uk/Product.do?method=view&n=345&p=175386&c=215&utm_source=Google&utm_medium=Base&utm_campaign=Handlebar%20Accessories&gclid=CLD6v6aE7sQCFWzHtAodKR4Azg

Yes, a friction control will do a similar job, but I don't think the lawyers would approve of gumming up the throttle return with a rubber band as a substitute.  :D

I don't know if there is a why or why not to this inquiry yet, and the dash is immaterial (literally).  Let's assume the bike is wrecked and the efi wiring and components are randomly damaged or missing.

[beetle]

If this is going full hypothetical, then why not go to a 3rd party fully programmable ECU? You could configure idle control any way you choose.

[rodekyll]

The practical end of the hypothesis is to drop a 1200 into the rodekyll, which is a '76 Convert.  I'm studying up to see if I can use the intake and exhaust stuff from the Jackal engine already there.  If I can bolt up the throttle bodies and exhaust, get a Convert timing cover and flywheel fitted, and somehow shoehorn a larger alternator up top, I might do it.  If there's something about the engine that won't let me do those things, the expense will stop me.  I thought understanding the 5AM would be a good starting point.

[beetle]

Gotcha. Well, in that case either the 5AM or the 15M would suit your purposes. Sounds like a an interesting project. I get why the dash is immaterial now.  :D