Hi Guys. Ive been really hacking up my timing tables trying to get rid of my low rpm low load bucking with my f-13 cam. Ive got my idle cells right at 30º timing, and immediately after them, it ramps up to around 40º. The top left corner of my table looks like this:

30 30 30 35 39 39 40 40 41 42 43
30 30 30 35 39 39 40 40 41 42 43
30 30 30 35 39 39 40 40 41 42 43
30 30 30 35 39 39 40 40 41 42 43
30 30 30 35 39 39 40 40 41 42 43
30 30 30 34 38 38 39 39 41 42 43
30 30 30 33 35 36 37 38 40 41 43
28 28 28 31 34 35 36 37 39 40 41
26 26 26 29 33 34 35 36 38 39 40
25 25 25 28 30 32 34 35 36 38 39
23 23 23 26 29 31 33 34 35 37 38

Its taken away some of the bucking but occasionally I still catch a bit of it. Both the high and low octane tables, plus both base timing tables, and the max torque timing table all mirror the same values. What can I do to get rid of the remaining bucking? Should I put even more timing in? How much is too much? The cam is a 230/232 .595/.585 112 +4

Thanks! -Tony

 

As you know we are chasing the same thing. I have some experimenting going right now with some help, will keep you posted.

 

Email me your file and i'll take a look at it. (cia_navl@yahoo.com )

 

Here is my timing table (entire). Note that the uppermost
left is decel only for me, my idle CylAir is about .17, between
3rd and 4th row and idle is 700RPM (between 2nd & 3rd
column).

I did not push on the idle-range cells the way I did on
PT/FT spark.


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I emailed you a copy of the file. I also posted it for you or anybody else who wants to critique it and/or point me in the correct direction.

http://www.ihearyou.com/~tony/tuning/10-16-05_a.bin

Please note that this is not a polished file by any stretch. Im still experimenting to see what helps and what dosnt. Im still playing around with the spark tables but lately ive been looking at fueling to eliminate the bucking. Most recenly I started lowering the o2 rich/lean switchpoints because my headers really cool off the o2 sensors. I also bumped up the gain a little. I also enlarged the integrator delay because the o2 sensors with headers are located further down stream. Raising the switchpoints seemed to help with the bucking but i think its more of a coverup, so i lowered them all from stock to make the o2 sensors more accurate. Now my part throttle seems to be much more snappy, but the bucking is still there.

Thanks for all the help guys!

 

lower?? I've had to raise the swith points on all the cars I've done with headers to get the fueling correct

 

See, Ive heard conflicting information on how the cold actually affects the o2 sensors.

Some say that a cold o2 sensor reads rich, meaning that a normal reading of stoich would result in a voltage of higher than 450 mv. Just as a WOT airflow of 12.8:1 results in 900 mv.

Others say that cold o2 sensors actually read lower than 450 mv at stoich, and that the computer sees this as a lean condition and overcompensates thus resulting in the rich condition.

I chose to follow the second idea simply because the stock bin has lower switchpoints at low airflow modes. I figured the stock exhaust manifolds would be cooler at low airflow than they would be at higher airflow.

Please let me know which one is actually correct here.

Thanks,
-Tony

 

The maximum output voltage first increases when
coming up from cold, as the chemical cell first
overcomes leakage losses, then decreases w/ temp
as you go up from there. What you're tying to deal
with is the low end, where a current-starved
sensor input might fail to get over half a volt.
But anywhere in the warmed up range the sensor
will switch abruptly through 0.5V and picking 0.3,
0.4 or 0.6 will make only a point or two difference
in a narrowband loop's center AFR.

Then again, a sensor that's failing to put out 0.5
is probably only another 50-100 degrees of exhaust
heat from failing to cross 0.4 either. The real solution
to these problems is to fix the heat loss, not crutch
the sensor electronics at the back end.

 

Thanks jimmyblue. Its not that the sensors are stuck towards the bottom at low airflow. The sensors are swinging well past 500 mv. Theyve always worked correctly, Im just trying to get them to be a little more accurate.

 

Any luck with solving the bucking? I did some messing this weekend and have not gotten it yet. I don't know about you, but when the bucking starts it sometimes gets steadily worse until you give it some gas or push the clutch in.

FWIW, I have similar timing as you posted above. Has not cured the bucking, but man it woke teh car up down low. First gear just spins everywhere now.

 

nope, no real cure for the bucking as of yet. Its always the worst in a slow second gear right hand turn. When I can get rid of bucking there, ill consider it gone. But like you said, off idle response is nice now.

 

I do not know the history of your problem, so I am going to ask about your VE tune. Is it dead-on??? I ran a F13 (112+4) this summer and had bucking until I got my VE table dialed in...

 

My VE table is dead on except in upper left area (like 800-1600 rpm, 30-50 MAP; my LTFT values are in the -5 to -12 range, but I have adjusted VE twice to get them closer to 0 and they have not changed

Other than that my VE table is excellent, nearly all 0, with a couple -1 values.

 

I also keep my VE table as spot on as possible. I have all 0 and -1's, even in the uppse left. Although every time I change my o2 switchpoints my low rpm low map cells come off target a bit until I re-tune the VE table again. In any case, my VE table hasnt helped bucking much.

 

Hey Guitsboy, can you send me your secondary VE table in an excel file. I would like to compare if you don't mind.

email: bowtieman81@aol.com

 

Sorry man, I dont have a secondary VE table. Its a 2002. A few posts up I linked to my .bin file.