Bucking under light acceleration

allen22 · Post by **allen22** » Wed Aug 30, 2006 3:32 pm

Hey,
Just went for my first quick test drive, using MSII V3 with EDIS6 on a DOHC 3.5L V6. It was bucking pretty bad under light acceleration, about 40 mph or so, light pressing of the throttle to accelerate slowly. Would this be an AE problem or VE table too lean? Should I have the AE turned off? I intend to use autotune with my LC1 wideband.

Seems like I should turn off AE for now so it's not an issue yet and I think I read that but, I'm swimming in Mega info right now, kinda drowning actually!

Any help is greatly appreciated!
Fred

Bernard Fife · Post by **Bernard Fife** » Wed Aug 30, 2006 3:38 pm

Fred,

It could be either a AE problem or a VE table issue. My bet is on the AE needing to be higher, if it only happens when accelerating. Try doubling the lower rate AE values and see if that helps.

I tend not to turn the AE off, as this can make drivability terrible while sorting out the VE table. Instead, I am careful to only adjust the VE table for constant conditions, using different gears and hills (or use the brakes) for different loading and rpm to tune the VE table.

Then I set the AE mostly in the driveway, with the 'minimum pulse widths that gives snappy reving in neutral' technique described in the manual (in fact, it's a good idea to do this every time you make significant changes to the VE table).

Lance.

allen22 · Post by **allen22** » Wed Aug 30, 2006 6:22 pm

Thanks sir, I'll follow your advice.

When you say use the "minimum pulsewidth" you mean the second verticle column in the AE wizard window right, the Value (ms) columns?

Do you usually mess with the fields at the bottom of that AE wizard much?

thanks again,
Fred

allen22 · Post by **allen22** » Tue Sep 05, 2006 12:19 pm

Ok, doubled my lower AE numbers and it revs up pretty good while idling (did before too though) has a very slight delay from the time you push the pedal to when it revs but that's not too bad of a thing really.

But, it still bucks when I try to accelerate on the road unless I accelerate very slowly. I think I'm just plain old too lean, does it sound like that to you guys?

thanks
Fred

allen22 · Post by **allen22** » Wed Sep 06, 2006 1:21 pm

Ok, I was given a fuel and ignition map from a friend with a similar engine setup as mine. The fuel map was quite a bit richer than mine and the spark map was quite a bit more advanced. The car no longer bucks on acceleration and revs up/accelerates pretty darn good, (too bad my exhaust sucks and is making it hard to feel how the motor is pulling).

I think my whole problem before was just too lean on the fuel map.

thanks,
Fred

wes kiser · Post by **wes kiser** » Sat Sep 16, 2006 3:07 pm

Just as a general reference point, lean will normally buck (engines will act quite smooth and happy right up to the rich run limit).

Another trick to smooth out bucks under extremely light acceleration is to pull timing. Ideally you want/need lots of timing at low map pressures. I find that in practice pulling timing lower than ideal under conditions control and smoothness is more important than peak efficiency makes for a much smoother, less jumpy car. I am not talking about pulling back to 10 degrees or anything, just less than ideal.