Bucking problem
Bucking problem When I put the new cam in, it started bucking slightly at the same point every time...
So I went and logged it last night, and I was looking at my fuel trim histogram, and it's bucking back and forth only between 2 cells. I don't know what that actually tells me, but I'm hoping someone can educate me about this, and let me know what I need to do to help or stop it from doing this.
So I went and logged it last night, and I was looking at my fuel trim histogram, and it's bucking back and forth only between 2 cells. I don't know what that actually tells me, but I'm hoping someone can educate me about this, and let me know what I need to do to help or stop it from doing this.
What kind of setup are we talking about? Year/Mods...It appears you have data logging capability, which software package do you have? With no info, I can only guess you are going lean in the affected areas. What parts of the tune if any have you tried yet? More info= more answers.
Originally Posted by Doc
What kind of setup are we talking about? Year/Mods...It appears you have data logging capability, which software package do you have? With no info, I can only guess you are going lean in the affected areas. What parts of the tune if any have you tried yet? More info= more answers.
It's a 99, cam, intake, headers, exhaust (or lack there of, lol), converter... just the usual stuff really. HPTuners is the software I'm using, and you are correct, it is lean in those areas. However, it was also lean in other areas and wasn't bucking.
The car has been tuned before, when I had a smaller cam, mid length headers instead of the longtubes, and a catback exhaust. I haven't changed much since then. I did add a little fuel to it, but before I try to address this problem, I want to learn more about what actually causes it and affects it and helps it.
Usually, it's due to not enough fuel/timing or the timing is jumping around. I'm guessing the bucking you're feeling is when the torque converter is locked and you're under 2000rpms??? First, get your fueling dialed in the best you can (use the instructions in the stickies). Log the grams/cyl. of airflow and rpms where you're feeling the bucking. See if you can smooth it out in the high octane table if it's jumping around so that there's a consistent amount of timing being comanded for that area. For example, my friend's car would buck under 2000rpm and under .20 grams/cyl of airflow because the timing would jump between 41 and 38 degrees. Setting it to a constant 40 degrees until the torque converter unlocked helped with a lot of it. But, it would still buck some. I'm up to 44 degrees in that area now and it's almost all gone.
Welcome to the club. Do a search and youll find WAY more info on cam bucking than anyone could ever type here, but sadly theres no definitive way to eliminate it. The extra spark and fuel will supress it, but most of us are still searching for the holy grail of non bucking tunes.
Originally Posted by Doc
I found the grail with a Road Runner. 
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I was able to eliminate my bucking by fatning up the AFR in those areas. You can raise the VE value in those areas, or if using EFILive's OS3 or OS5, you can change the commanded AFR in those areas to be richer.
This of course assumes you've steadied your spark in those areas and the spark is optimal.
On the matter of lean in other areas and not bucking, it has more to do with the effeciency of the cam. In your bucking range, you're in least effecient area of the cam (reversion effects).
This of course assumes you've steadied your spark in those areas and the spark is optimal.
On the matter of lean in other areas and not bucking, it has more to do with the effeciency of the cam. In your bucking range, you're in least effecient area of the cam (reversion effects).
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Bucking Actually what I have found is there is too much fuel and or too much timing, All cases are different, If you have large injectors and a healthy cam this will happen, but it can be eliminated. I run 85lb injectors in my LT1 and had tremendous bucking at 40mph. it is all gone with a combo of timing, fuel changes. Also you can datalog the maf frequency at the speed where the bucking occurs and work that area of the table only so as to not affect fueling at WOT...
Originally Posted by SSpdDmon
Usually, it's due to not enough fuel/timing or the timing is jumping around. I'm guessing the bucking you're feeling is when the torque converter is locked and you're under 2000rpms??? First, get your fueling dialed in the best you can (use the instructions in the stickies). Log the grams/cyl. of airflow and rpms where you're feeling the bucking. See if you can smooth it out in the high octane table if it's jumping around so that there's a consistent amount of timing being comanded for that area. For example, my friend's car would buck under 2000rpm and under .20 grams/cyl of airflow because the timing would jump between 41 and 38 degrees. Setting it to a constant 40 degrees until the torque converter unlocked helped with a lot of it. But, it would still buck some. I'm up to 44 degrees in that area now and it's almost all gone.