Post your tips on eliminating bucking here!
Originally Posted by pyro
what is the major advantage to efilive?
www.efilive.com
www.efilive.com/forum
Thread Starter
Joined: Apr 2003
Posts: 2,597
Likes: 4
From: Lawrenceville, GA
Originally Posted by Tomcat
Bill , do you have spark smoothing turned off , give it a shot with it turned back on , helps heaps on cammed stuff usually.
Thanks.
Bill
Last edited by Bill Bowling; Aug 19, 2005 at 09:40 PM.
I cut and pasted my high octane table to the idle spark table from 600-1600 rpm and 0 to .2 g/cyl and it seemed to help. I think it was transitioning between the two when i was at around 1% throttle and causing bucking.
Thread Starter
Joined: Apr 2003
Posts: 2,597
Likes: 4
From: Lawrenceville, GA
Originally Posted by P Mack
I cut and pasted my high octane table to the idle spark table from 600-1600 rpm and 0 to .2 g/cyl and it seemed to help. I think it was transitioning between the two when i was at around 1% throttle and causing bucking.
Thanks,
Bill
A while ago I advanced it and i thought it helped but couldn't tell a whole lot of difference. The next thing i'm going to try is using the spark adder under vcm controls to see exactly how much more timing it likes. Hopefully with realtime control i'll be able to compare easier.
Another thing i'd like to try is making the timing "ramp up" steeper, or go the other way with a constant value, but that will take a lot of trial and error.
Another thing that i think might be happening is a driver induced oscillation (like pilot induced oscillation in flying). When the car bucks forward the weight of your foot pulls back slightly causing the car to slow down, causing your foot to go forward, etc. I'm not sure if this is really going on or not but i thought i'd throw it out there.
Another thing i'd like to try is making the timing "ramp up" steeper, or go the other way with a constant value, but that will take a lot of trial and error.
Another thing that i think might be happening is a driver induced oscillation (like pilot induced oscillation in flying). When the car bucks forward the weight of your foot pulls back slightly causing the car to slow down, causing your foot to go forward, etc. I'm not sure if this is really going on or not but i thought i'd throw it out there.
Thread Starter
Joined: Apr 2003
Posts: 2,597
Likes: 4
From: Lawrenceville, GA
Originally Posted by RedHardSupra
so which way did you change the timing to fix the bucking? or is there more to it than that?
Bill
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Originally Posted by P Mack
Another thing that i think might be happening is a driver induced oscillation (like pilot induced oscillation in flying). When the car bucks forward the weight of your foot pulls back slightly causing the car to slow down, causing your foot to go forward, etc. I'm not sure if this is really going on or not but i thought i'd throw it out there.
Last edited by TAQuickness; Aug 21, 2005 at 06:58 PM.
getting the bucking to go away and getting it right can get time consuming. each timing chnage will change your ve. a small change in ve or timing will also change the smoothness of the car a good bit. you have to look and see wahts going on at the bucking. a lot of it has to do with transitions from idle cells to dricing cells. this switch will cause changes in timing and fueling. most bucking is a direct result of this. any idle airflow tables that are off, timing tables, ve cells, will all contribute to it. last time i let out the clutch and rolled will small amounts of gas teh car bucked slightly but has gotten better. i havent checked since my last changes but driving in and out of the garage, the extent of my driving, has shown its a lot better. right now i can let the clutch out to try and stll the motor and it wont stall. once i throw the clutch in the rpms recover without much of any overshoot (nothing you can actually hear only see the extra 50 rpms in the log)
like i put in RHS's write up, i think something should be included about how STEPS need to be taken. each car is different of course but if you only change certain things at certain times it makes it a lot easier. when doing these changes you dont really want to ever mess with the ve table. ve chagnes throw off airflow calculations at idle, those problems will just carry over into anything else you do, as many of you all know its very touchy when you start to get clsoe
like i put in RHS's write up, i think something should be included about how STEPS need to be taken. each car is different of course but if you only change certain things at certain times it makes it a lot easier. when doing these changes you dont really want to ever mess with the ve table. ve chagnes throw off airflow calculations at idle, those problems will just carry over into anything else you do, as many of you all know its very touchy when you start to get clsoe
OK, since I am having bucking too I will chime in. I will first say that the bucking improved once I got my idle straightened out. My IAC counts are now at 30-35ish, where they were hovering around 75 at hot idle.
But I still have the bucking. I am curious to see the timing/ve table for those that have cured the bucking. I have had a heck of a time getting my ve table right in the idle-1600 rpm range. I still get LTFT values of ~-12 in this region. After 1600 rpm my VE looks awesome.
But I still have the bucking. I am curious to see the timing/ve table for those that have cured the bucking. I have had a heck of a time getting my ve table right in the idle-1600 rpm range. I still get LTFT values of ~-12 in this region. After 1600 rpm my VE looks awesome.
Well, when you boys figure it all out, hook me up! Im still having trouble with the bucking, but I think tuning is out for a while since they recently suspended local ethanol mixed gas (why tune for reg gas when e-10 is coming back soon?)
Originally Posted by technical
Rich mixture can also cause bucking/tailgating.
I just put my throttle cracker and throttle follower back to stock and the slight bucking I have at 1100-1200 is almost all gone.
Keys for me running practically surge free:
MAFless tune.
VE tables nailed.
Lots more timing at idle (32 degrees on all 4 spark tables at lower rpm)
IAC counts of 30 at idle with AC off, 80-90 with AC on. (combination of drill mod and throttle blade mod).
Base running airflow levels correct.
But in my opinion, the biggest contributor to ending my bucking and surging was re-doing my IAC Effective Area table. Now my Calculated Airflow (dynamic based off of VE tables) and my Desired idle airflow (Des IAC) match at various temps and airflow from 0 IAC to 150 IAC. If they don't match across all these IAC ranges, you've got room to improve. Engaging the AC should make no difference. The two airflows should still match.
Keys for me running practically surge free:
MAFless tune.
VE tables nailed.
Lots more timing at idle (32 degrees on all 4 spark tables at lower rpm)
IAC counts of 30 at idle with AC off, 80-90 with AC on. (combination of drill mod and throttle blade mod).
Base running airflow levels correct.
But in my opinion, the biggest contributor to ending my bucking and surging was re-doing my IAC Effective Area table. Now my Calculated Airflow (dynamic based off of VE tables) and my Desired idle airflow (Des IAC) match at various temps and airflow from 0 IAC to 150 IAC. If they don't match across all these IAC ranges, you've got room to improve. Engaging the AC should make no difference. The two airflows should still match.
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2013 Corvette Grand Sport A6 LME forged 416, Greg Good ported TFS 255 LS3 heads, 222/242 .629"/.604" 121LSA Pat G blower cam, ARH 1 7/8" headers, ESC Novi 1500 Supercharger w/8 rib direct drive conversion, 747rwhp/709rwtq on 93 octane, 801rwhp/735rwtq on race fuel, 10.1 @ 147.25mph 1/4 mile, 174.7mph Half Mile.
2016 Corvette Z51 M7 Magnuson Heartbeat 2300 supercharger, TSP LT headers, Pat G tuned, 667rwhp, 662rwtq, 191mph TX Mile.
2009.5 Pontiac G8 GT 6.0L, A6, AFR 230v2 heads. 506rwhp/442rwtq. 11.413 @ 121.29mph 1/4 mile, 168.7mph TX Mile
2000 Pewter Ram Air Trans Am M6 heads/cam 508 rwhp/445 rwtq SAE, 183.092 TX Mile
2022 Cadillac Escalade 6.2L A10 S&B CAI, Corsa catback.
2023 Corvette 3LT Z51 soon to be modified.
Custom LSX tuning in person or via email press here.