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Jerky standing starts

John in PA

John in PA

Cruisin' Guzzisti
GT Contributor
Joined
Jul 31, 2009
Messages
255
Location
Hollidaysburg, PA
I have Todd's full upgrade, ECU, PC-V, Auto-tune. I running a Mistral end can, and stock airbox with K&N filter. Bike runs fantastic, except one area. Warm engine, starting from a standing start, or re-engaging clutch at walking speed, Normal RPM's for the task, but as clutch engages and RPM drops to 1750 or so (very predictable on the RPM's) I get a "drop-out" of engine power, almost like it's off, for a half second, then it kicks in again with a significant jerk. On a bad surface, this would be a hazard. Also looks amateurish when riding, but mainly just unpleasant. I could deliberately rev higher and slip the clutch more, but the bike really shouldn't behave like this, and I really don't like abusing the clutch. I checked autotune values and I have good values all throughout the low rpm/low throttle opening range.
Could this be a stepper motor issue, with the stepper motor changing mixture significantly during brief idle periods, with the computer needing a "lag time" to make up the difference, or should I look elsewhere?
Not TPS, as same throttle openings anywhere else in operating range produce no flaws.
 
John,

You have been around Guzzi's a lot longer than I have, me being only one year. But my Stelvio has done this type of thing two or three times during the course of my one year ownership. Each time I found a lot of slop in the push / pull throttle cables. I took out the slack and the problem disappeared. I know it sounds simple but that was the fix. Remeber the KISS rule, sometimes it's that simple.
 
Kurt, outside of all above, accept the AT revisions, and send me the map so I can have a look there as well for you.
 
I had a similar situation. The problem was my map. In my desire to tinker frequently I was accepting trims a lot and I found that the AT kept removing fuel from some of the low rpm 2% cells. The map was all the way down to -50 in one cell there. Every time I would reset the map back to the base it would go away. The solution... I got a map from Todd and stopped messing with it so much :) I think my normal commute might be too short and have too much stop and go traffic for me to accept the trims all the time with the AT.

Dan
 
Thanks for the replies. i believe i calibrated the throttle, but I'll recheck. Dan, i bet that's the issue. I also have accepted half-dozen or so trims, but have been doing a lot of commuting type driving. Maybe i'll check the map (I only checked the A/F targets) and see if there are any goofy readings in the low TPS areas around 1500-2000 RPM and manually tweak if they are.

Todd, once i get it back to it's happy place, do I put zeros back in for the A/F targets in those cells to make the AT stop adjusting?
 
John,

I noticed that mine is still doing this same thing and the throttle cable are tight, almost guitar string tight. I haven't tried any autotune tricks yet. I'm hoping you'll find a solution so I won't have to hut my brain thinking for myself.
 
John in PA said:
Todd, once i get it back to it's happy place, do I put zeros back in for the A/F targets in those cells to make the AT stop adjusting?
Click to expand...
Yes, I'll gladly adjust the map if you send it to me... kmartin, you as well.
 
I've got the autotune and all, Todd. I should be able to make any needed adjustments myself in the A/F table and let the autotune do the rest, shouldn't I? I just haven't bothered to do anything. It hasn't been bad enough to mess with yet.

I'm still not convinced all is correct, as I have that problem above about 7500 rpm where it acts like a rev limiter. I'm hoping to have someone take it for a ride in Az in a few weeks and tell me I'm all wet, or not.
 
Food for thought! I had the same stumble and found that my spark plug boot was arching/grounding intermittently, this led to a stumble as you have described. Them damn spark plug boots "suck". I say check, them if its them easy fix.
Good luck.
 
I finally got a chance to tinker with the maps at the 0-2-5-10 % throttle opening settings. I especially focused on settings either side of 1750 RPM since that is where the stumble occurred. What I found is that fueling had been inappropriately leaned out in those areas. I added about 20 points to each cell where suspiciously low numbers were found. I had saved each map before accepting trims, so I looked at previous maps in those areas and loosely compared values. I then manually adjusted the values in the desired cells and sent the map to the PC-V. Problem solved.

Why the problem? I believe i was doing most of my riding as a 12 mile commute with short rides. Saving trims after these rides may not have reflected the changes needed to a map for a fully warmed engine. I'm not going to save any trims unless I've thoroughly warmed the bike first (maybe 50 miles or more, Todd??) Or should I just put zero's (or leave blank??) the A/F ratios in the low throttle area of the autotune?

Anyhow, the problem is solved and it was an A/F problem, too lean in the cells around 1750 RPM
 
John in PA said:
I finally got a chance to tinker with the maps at the 0-2-5-10 % throttle opening settings. I especially focused on settings either side of 1750 RPM since that is where the stumble occurred. What I found is that fueling had been inappropriately leaned out in those areas. I added about 20 points to each cell where suspiciously low numbers were found. I had saved each map before accepting trims, so I looked at previous maps in those areas and loosely compared values. I then manually adjusted the values in the desired cells and sent the map to the PC-V. Problem solved.

Why the problem? I believe i was doing most of my riding as a 12 mile commute with short rides. Saving trims after these rides may not have reflected the changes needed to a map for a fully warmed engine. I'm not going to save any trims unless I've thoroughly warmed the bike first (maybe 50 miles or more, Todd??) Or should I just put zero's (or leave blank??) the A/F ratios in the low throttle area of the autotune?

Anyhow, the problem is solved and it was an A/F problem, too lean in the cells around 1750 RPM
Click to expand...


John

I would be interested in looking at the map that you are running now if possible.

If you would be so kind as to send me the Pvm file via E-Mail

draidt@tampabay.rr.com

Thanks.
 
I'd be glad to send the map. I should mention engine/exhaust configuration, in case we're not running apples-with-apples.
I've got the stock airbox with a K&N filter, Mistral C/F conical slip-on with slightly relieved baffle (a few extra holes in the supplied baffle). That close to what you're running?
 
John in PA said:
I'd be glad to send the map. I should mention engine/exhaust configuration, in case we're not running apples-with-apples.
I've got the stock airbox with a K&N filter, Mistral C/F conical slip-on with slightly relieved baffle (a few extra holes in the supplied baffle). That close to what you're running?
Click to expand...


Close except for an open air box.

Thanks
 
From past experience with a Centauro, an open airbox makes a rather large difference in mapping. I'm still willing to send the map if you think it would be useful, but be prepared for some rough running possibly. Do you have the Autotune? if so, it will eventually straighten it out, apparently with the caveats in my previous post about saving trims on a relatively cool engine.
 
John in PA said:
From past experience with a Centauro, an open airbox makes a rather large difference in mapping. I'm still willing to send the map if you think it would be useful, but be prepared for some rough running possibly. Do you have the Autotune? if so, it will eventually straighten it out, apparently with the caveats in my previous post about saving trims on a relatively cool engine.
Click to expand...

John I have been a tinkerer (an unskilled person who tries to fix or mend ) all my life :mrgreen: Right now I am happy with my set up but would like to compare the maps.
 
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