Bucking on throttle application?
 

Is there a common cause in a tune to cause forward/backward bucking on partial throttle after an upshift?

No offense to you sir but from the outside looking in that kinda sounds like sloppy driving on a MT car considering it's right after the upshift. Assuming it isn't, however, do you have a way to log misfires perhaps?

The way it’s worded it does sound like you’re popping the clutch and that will most certainly cause the car to buck. To play devils advocate, how much throttle application and at what rpm are you experiencing this? Datalogs would be ideal.

Could very well be. I'm driving an AT in semi-manual mode and it usually happens when I short shift out of 1st at around 2k and have to let up off the throttle due to traffic. Part of it is my foot pulsing the throttle when it's bucking, causing a positive feedback loop. I think this is a log zoom of the event:
https://datazap.me/u/protoformx/log-...8&tmax=3248.08

Cold starts in first gear used to get "bucking" but only randomly. I also had this issue in a civic si. It's either my user error or bad gasbin my area? I don't know as it happened with steady gas in first gear only when cold. Left foot not even close to clutch. Oh well.

from what i can see the moment you stepped on throttle it ran momentarily lean and then rich before it tried to match the target afr which is why you have this issue,


i think you might just need to adjust the transient enrichment.


which tune are you using?

It's the v4.03 OFT Stg1 OTS.

did you edit the tune for your car? did you scale the maf sensor?


this could be it

I had this issue, I’m sure things in tune can be optimized more BUT,

It drastically improved once I let the car idle until it was under 1k before driving. Takes about 3minutes, so cant just turn on and go right away like before.

I did. Today's tune finally has load comp, IAT comp, and now a higher threshold for throttle tip-in (4% vs. the OTS 1.5%) based on your comment on transient enrichment. The bucking seems to have really been tamped down, almost eliminated in fact. Not sure if there is some other table to better adjust transient enrichment with regard to actual fueling compensation rather than the threshold for using compensation.

the most important part of tuning any engine is making sure the actual afr is matching the target afr,


in this engine you only have to adjust the maf scaling, to get the best drivability you want to get your fuel trim as close as +-2% in closed loop, +-5% is what most tuner shoot for atleast, some people would say +-10% is still acceptable but i personally think its way off, now the fuel trim could be different from day to day so try to do it all in one day if possible


if the fuel trim gets a bit worse after couple of day but the drivability haven't changed leave it as its.


now for the wot try to get it as close as 0% or atleast 2% the smoother the graph the better it would feel, one of the things i notied this week is my wb would read 12.46 and my front o2 would read 11.8 and when my wb read 11.8 my front o2 would read 11.2 which tells you the stock o2 is not accurate even with n/a engine so try to tune by feeling and engine sound,


what i mean is find the afr that your engine likes and pulls the hardest from 2000-rev limiter and as long as it doesnt stumble or knock its good, and by sound sometimes you can hear how bad the engine is running if its too rich or too lean

This is after about 4 days on this tune:
https://datazap.me/u/protoformx/log-....14&tmax=14.89
AFR is from the stock sensor.

So looks like i'm just shifting at the wrong times and/or with the wrong throttle angle.

I get that too, only on cold starts. One of those it is what it is things. I used to think it was driveline lash/tolerances but i bet it's a side effect of emissions related krap.

Try to log ignition timing. Could be too much transient ignition retard.

When you make the log, do something identifiable after you experience the bucking so it's easy to pinpoint where in the log it happens. E.g. you could go full throttle a few seconds after it happens, conditions permitting. Then it's easy to find in the log.