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Stepper Motor Bypass

seb

seb

Tuned and Synch'ed
Joined
Apr 12, 2009
Messages
61
Location
Bellingham, WA
I have been unable to get Todd's attention via his email. So maybe someone else knows what parts I need for the stepper motor shutoff. During my rather long trip last month, the idle became erratic after some extended high speed runs. I am assuming that the stepper motor bypass valve is the fix to this problem? Could someone please elaborate on this?
 
Steven, sorry, yes the stepper motor controls idle, so either my kit or whatever means you choose to eliminate the airflow to the valve is what needs to be done. I can now also delete the input code on the ECU for those choosing to remove it.
 
I am quite reluctant to remove the ECU for re-programming as this is a chore. Why would I eliminate it? The stepper motor is also used for cold weather starts, I assume? How do I order the kit?

S....
 
Steven that is true, and order details are here; https://www.guzzitech.com/store/GT-SMK.html - I only have them in stock for the Norge currently, as I am out of switch holders at the moment. If you'd rather do a check, PM or e-mail me; Todd at GuzziTech.com
 
As a new MG owner, new for me 2007 Norge, can some one tell me the basics of the stepper motor problem. I understand from the forum that the motor controls the idle nad that new, revised and or better units are available. Do these units use the same basic "motor"? Thanks.
 
Some bikes have proven problematic for erratic idle. There is no newer stepper unit that I am aware of. I offer a kit to vary the air-flow, or like others you can install a manual valve. For more on function...

GuzziMoto said:
The stepper motor has two different reasons for being on your motorcycle. One is to assist in maintaining idle at different temps and loads (on cars it even has to deal with huge load changes at idle due to things like the AC compressor kicking on and off, we should only see small changes of load). The other function it performs is to reduce emissions by cracking open when you are decelerating from higher rpms (throttle closed). This maintains whatever target air/fuel ratio some engineer has determined is best for emissions. This aspect of it can slightly reduce the amount of engine braking (compression braking) since the effect of this is much the same as cracking the throttle open slightly (or even setting the idle a little high).
The stepper motor as it came on my Guzzi cannot tell one cylinder from the other, it has one output that T's to go to both throttle bodies. It could open and shut at low throttle openings to cycle the mixture back and forth, rich and lean, as this does help the cat work properly. But since the O2 sensor and ECU normally work in that fashion anyway I would be surprised if they use the stepper motor for this (I am not sure it can even respond fast enough to do this). And obviously its effect would be diminished as you open the throttle.
I did a manual switch to turn mine on and off (before the kit existed). This allows it to assist in cold starting the bike but then I can turn it off and maintain a more stable idle and the shifting feels slightly better possibly due to the slight increase in compression braking. Yes, that last one could be in my head as feel is hard to quantify (but if it is in my head I am not alone as others have reported the same thing) but the more stable idle is definite.
Click to expand...
 
Gday, my 06 Grrrriso is a right royal P.I.T.A. to balance the T/B's, there is a higher vacum in the left side at idle and a higher vacum in the right at 3000 RPM and beyond. I have checked valve clearances and they are spot on and have been that way for quite a while now (20-30000 k). I have set and reset the TPS ad infinitum with my VDST (greatest thing since canned beer). So I fitted a manual in line valve thinking the stepper motor was up to no good. However if I shut the valve at either idle or 4000 + RPM with the engine at working temp he sorta dies in the arse. I have not done a compression or leak down test but looked up thru the sump the other day and all looks fine , he only uses about 250 ml of oil over 5000 k's. Could someone enlighten me (you may need a big stick) as to why my stepper isolater behaves this way, please.
 
Indeedy so I have tried to balance T/B's. I use a home made manometer and have swapped the hoses over with the same result. Before I had my own VDST one bike shop used a mercury type and another a gauge type, same result.
 
How are you hooking your balancing device up to the bike? Usually you disconnect the stepper motor and hook to the ports on the intake manifolds.
If you close off the stepper when warm and it will not idle then something is wrong. If it dies at 4,000rpm when you shut the valve something is really wrong.
You should not need to close the stepper motor to balance the TB's. There is a air bleed screw for idle balancing and a adjustment in the linkage for the higher speed balancing. That allows you to go one way at idle and the other way at 3,000 rpm.
 
I use 2 drilled 6mm bolts ,with their heads cut off and 2 nuts locked on each other, screwed into the holes in the intake elbow near the flange at the head end of elbow. I dont isolate the stepper when balancing as this is not isolated in service . I use the linkage rod end screw on LHS for 3000 rpm and air bleed screws for idle. He will not idle with stepper isolated and if isolated while riding he runs poorly and lean.
 
Well, as I mentioned I don't think it would matter whether your stepper motor is hooked up or not unless there is something wrong with it as it is a single source with a T to split it to the cylinders. I do agree with your mentality of not disconnecting the stepper when balancing it unless you are not using the stepper motor in service. But I do not use the stepper except for cold starts.
I am not sure how or why turning off the stepper would/could make the bike run lean...
Many people including myself have had no issues and in fact have improved the way our Guzzi's run by installing a device to turn off the stepper motor. Something is not right with yours, but I am not sure what it is.
As for the inability to balance the TB's, maybe you have an air leak. Have you maxed out your adjustments and not been able to balance them? Aside from an air leak I can't think of anything else that would cause this.
 
I have found tthe stepper is not shutting off,thus connecting the two inlet tracts , ala Triumph twins of days gone by. I have put a 1/4" ball bearing in each hose from stepper "T" to T/B.I will see how it goes shortly.
 
I don't follow you. The two inlet tracts are connected by hoses that T together and then from there it goes to the stepper motor. Whether the stepper is open, closed (if it ever actually closes), or some state in between, the two inlet tracts are always connected.
That is why I put a valve between the stepper motor and the airbox, so I could turn off the air supply to the stepper motor. So when I close the valve it does not matter what the stepper motor does, it has no ability to add air to the inlet tract and lean out the mixture. The two inlet tracts are still T'd together and that is fine, I have not had any issues caused by that. Some people have suggested that you need to disconnect the stepper motor to sync the TB's, but since you usually disconnect the stepper motor to sync them I have not worried about it. But in my opinion syncing the TB's with the stepper hooked up would be the way to do it if that is how it is in use.
 
I put the ball bearings tween stepper T and T/B's in the hunt for a cure to a miss/roughness my bike has.I fitted a manual valve tween air box and stepper,and when shut the bike runs "flat". I am in the process of removing them, they didnt do the bike any favours,although there semmed less muffler popping and the miss is still there. When balancing T/B's, following Graham 's excellent posts on this subject the R/H side shows a bias at 3000 rpm (and beyond)
that adjusting doesnt seem to fix. Syncing t/b's and resetting tps doesnt eradicate the miss.Valve clearances are 0.1 and 0.15 compression test showed 165 psi rhs and 155 lhs. I sprayed an ether based product all around both inlet tracts from air box to head with no rev increase. Outer spark plugs are set at 0.6mm.I have packed the engine temp sensor. My next step is to replace the inner plugs and remove t/b's and check for wear. My muffler is one I made but putting the OEM one back on makes no change to the miss.There are no leaks in the exhaust system. No mods to airbox and still the OEM map to suit an 06 1100.
 
Wow, you sure have done a lot to try and fix your bike. Still don't quite follow you with the ball bearings, if you are trying to keep the intake ports from sharing vacuum, just remove the fittings the stepper motor T lines attach to and replace with normal, solid bolts. I don't think that is your problem, though.
Also, you say the TB's have been balanced but you describe an imbalance between the two that you were unable to correct. That tells me they are not balanced. That may be part of the problem, maybe not.
Also, you might try looser valve clearance settings, the standard factory settings are on the tight side for less noise. 0.20mm and 0.25mm are sometimes preferred.
I am not a fan of packing the temp sensor unless your bike has issues with poor fuel economy and slow warm up. Otherwise it tends to lean out the mixture.
Finally, your comment about the motor feeling "flat" with the stepper off..... Mine and quite a few others run better and crisper with the stepper off. If yours does not work well without the stepper then that also tends to say there is something wrong with the set up of yours. I would focus less on re-inventing the wheel and make sure the basics are right first. You say it has the original map, there have been a few maps. If yours still has the map it was built with that would be a bad thing.
 
I have had some success at getting rid of the miss, I set the TPS with a 0.1mm shim tween throttle stop screw and arm (as I read about here)which with shim removed puts TPS at 4.1degrees.Throttle balance closer but still not happy.I havent ridden him yet ,its raining here on NSW Mid North Coast. Hopefully I will be able to arrange to visit Mr Roper at his convenience and see about an upgraded map. Thanks for your help.
 
There's many Stepper Motor thread .... and this one comes close to the question I have. :)

Here’s a thesis on the Stepper Motor function that I put into practice.
I’ve been reading the threads about people having cold start issues with their bike and when the bike is running does not idle properly.

Living, working, sleeping, with control systems this problem was eating me!
Actually I was gaining weight from eating too much! :eek:hmy:

First the ECU is set to idle at +/- 1200 rpm.
This is monitored constantly by the ECU when the throttle is closed loop at 4.7 deg.
When the rpm deviated from its set-point the ECU sends a signal to the stepper motor to open or close the valve letting more air in or less air in through the TBs respectively, to maintain 1200 rpm. (OK everybody know this ….. ya, ya just bare with me!) :blink:

Since I have the VDST software to monitor the step value of the motor I decided to do some tests. Note initial stepper motor setting is 100 (And at open throttle goes to 100)
The following are closed loop valves at TPS 4.7 deg.
- To make the stepper motor close…I removed the air box cover leaving the filter in place…..simulating more air in and the step motor value = 51 close valve
- To making the stepper motor open…I blocking the snorkel on the air box…simulating less air in and the step motor value = 200 open valve

Here is where it gets interesting.
I started up the bike cold, the initial valve was 100 then all of a sudden the stepper went to 170, engine was bucking, the step value decreased to 90, engine stabilized, stepper went to 150, engine was bucking ….. did this till the engine temp was approx 50 deg C.
What’s more interesting is that on my bike when the engine is warm the stepper motor value decreases to almost a value of 60. (Valve CLOSED!)
In my books its working reverses acting …. The value 60 doesn’t bother me as much it’s the valve that is closed that is not right!!!

Example:
When engine cold ……the stepper should act like a choke. (This is why shut off valve on the inlet of the stepper motor helps)
If the ECU asks the stepper motor to open, open, open when the engine is cold more air goes in therefore idle decreases ….. and stalls. (Too much air….too lean)

I would think the stepper motor pin connection would be reversed. (RH coil with LH coil)
Would anybody validate this for me ….. if this is so?
Thanks
 
The flaw in your theory is that the ECU is also controlling the amount of fuel injected.
A cold engine requires a faster idle in most cases, so more mixture is supplied, by opening the stepper motor and increasing the fuel supply.
 
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