GuitsBoy

iTrader: (4)

I know there are a couple of individuals who still have some low rpm low load bucking with their cams, regardless of how much timing they throw at the motor. After researching some things, I ran across a post where someone said bucking was simply a harmonic being reached in the closed loop system, much the same way a microphone will feedback when held up to a PA speaker. I remember having some light bucking issues after doing my headers but before I installed the cam, so I was beginning to give this idea some credit. Anyway, I have played with two tables and all but completely eliminated my bucking. I still get a little bit in the usual places but its subdued enough so that I dont have to clutch in, I can just ride it out now.

HPTuners > Fuel Control > Open and closed loop

O2 sensor rich/lean vs. airflow
From: 366 436 436 436 451 501 501 551 551
To: 425 445 464 484 503 522 540 551 551

The saying goes that a cold o2 sensor reads rich, well, if thats the case, i figure lets try and switch where the o2 reads a little richer.

Closed Loop Integrator Delay
From: 1 0.288 0.175 0.15 0.131 0.119 0.113 0.106 0.1
To: 1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2

The idea here is that it takes longer to reach the oxygen sensors now that theyre moved further downstream. Lets reflect this here.

I also took the Closed Loop Mode vs. Airflow table from a vette which IIRC has its o2 sensors further from the heads.
0 1 3 8 9 10 11 12 14 14 14 14 14 14 14 14 14 14 14 14 14 14 14 14 14 16 16 16 16 16 16 16 16 16 16 16 16 16 16 16 16 16 16 16 16 16 16 16 16 16 16 16 16 16 16 16 16 16 16 16 16 16 16 16 16 16 16 16 16 16 16 16 16 16 16 16 16 16 16 16 16

This spaces the airflow cells (1-16) out further across the g/sec airflow table, giving us more area to play with.


!!! WARNING !!!
The numbers above are FAR from being dialed in... They were a first shot in the dark. For all I know they could be overshooting the correct values by quite a bit, however they did make a marked improvement in my car. Take all this with a grain of salt.

-Tony

GuitsBoy

iTrader: (4)

Well, I still have some bucking this morning, but its still better than it was before. Gong to play with the settings and see...

TAQuickness

iTrader: (28)

FWIW i'm running OLSD and can't seem to nip the low load/rpm bucking unless I throw more fuel at it.

I'm very interested to see what works for you.

Bill Bowling

iTrader: (6)

I am also still having some bucking. What tables do you think I should look at using FlashScan OLSD? I have moved the spark up and down trying to get rid of the bucking. I was thinking table B3647 might be the one to change or maybe the VE table.

Bill

Bill Bowling

iTrader: (6)

What table do you try? VE table maybe. How much higher do you go and what cells?

Thanks,
Bill

TAQuickness

iTrader: (28)

bill - i came across this when i disabled charge temp blending. it richened up across the board. Over all effect with it disabled was not to my liking so I enabled it again. At the moment my motor is out of the car so i'm not doing much tuning but, when it goes back together, I'll be upgrading to the V3 OS so I can add the fuel to the respective bucking cells.

The way I capture bucking is to get on a back road, set the scanner up, get the car to bucking, start logging, keep the car bucking as long as I can stand it, then stop the log. That way I have a nice clean log of nothing but bucking. Then you can go thru and set up your maps to see what table cells need adjusting. FWIW, my bucking got a lot better with a 13:1 AFR

Bill Bowling

iTrader: (6)

I am already running V3 OS. I will try the logging and then I could just set my AFR in those cells.
Thanks,
Bill

Bill Bowling

iTrader: (6)

That did not work. Still working on this problem.
Bill

ninobrn99

iTrader: (8)

any update to this?? under 2k mine is bucking like crazy! tried the ve, set the ifrs and left them as is. I havent messed with timing or open/closed loop settings yet..

GuitsBoy

iTrader: (4)

Well the first thing youre gonna need to do is get youre IFRs correct, then dial in your VE table.

After that, scale your switchpoints up just a tad, i put 0 back down to like 350 to try and get rid of the fumes at idle. The rest went up a bit.

Then, i started playing with the base numbers a bit. That way the fuel wouldnt swing so wildly.

Look at dynamic airflow and see at what g/s you get the bucking. Mine was around 16 g/sec. I then found what airflow mode corresponded to 16 and then referenced the base number and cut it in half. So far its helped a little, but not completely.

RedHardSupra

iTrader: (1)

care to expand about your logic and methodology on changing switchpoints?

GuitsBoy

iTrader: (4)

Although, I have no idea how valid my reasoning is, but ill certainly try and explain.

I have heard many people with headers mention that they had to up the switchpoints to get A:F right on 14.6. I figured this would make more of a difference at lower airflow modes, since at higher modes that gasses will be moving quickly enough to hit the o2's before the exhaust cools. My car idles at around 8 g/sec which equates to airflow mode 2, so i decided that I would lower the switchpoints at idle airflow modes (0 - 2) to cut back on my stinky idle.

Stock: 366 436 436 436 451 501 501 551 551
Modified: 351 366 436 458 477 497 514 534 551

I guess theyre not really moved up too far, its a little fatter around the airflow modes that buck... and atleast more linear. I had previously moved them all down because thinking that it would compensate for headers simply running rich.

Then theres my Mode vs airflow.

Stock: 0 1 3 8 10 11 13 14 14 14 14 14 14 14 16 16 16 16 16 etc.
Modded: 0 1 2 4 6 11 12 13 14 14 14 14 14 14 14 16 16 16 16 etc.

The idea here was to give the highest resolution right arond 16 - 20 g/sec which is where most of my bucking takes place.

Heres the part that I feel had the most effect in subduing the bucking. Its the Closed Loop prop base vs. airflow mode table.

Stock: 128 266 401 401 401 401 401 401 401
Modified: 80 90 100 110 128 251 301 351 401

This keeps the fuel from swinging so wildly at low rpms / low load, due to the lag time of having the o2s further downstream.

Also of not, I have my spark raised to the lower 40's in the bucking cells. Theyre relatively even and all the tables match.

RHS, please critique what looks valid and what is pure horseshit, cause to be honest, im just trying stuff at random at this point. ANd Ive tweaked so many things i dont know what does what anymore!

Thanks,
-T

soundengineer

iTrader: (16)

try lowering your closed loop proportional tabel values by like 25%
or even disableing Proportional all together
for normal and idle....I am tryingto see if I can come up with a method to :calculate this...not sure how yet....but I have found this to help sometimes...

WS6FirebirdTA00

iTrader: (33)

yep, prop fuel is where its at. go out and scan dynamic airflow and your o2s, when it bucks put a marker and at that marker look at the dynamic airflow. mine was mainly at 20 g/sec, which i set my airflow mode table up to use mode 8. then i went to prop fuel and took out 15 at a time until it went away in that cell. i have 42# fords and here are my values

Proportional fuel closed loop

4.00000
4.00000
4.00000
32.00000
62.00000
107.00000
297.00000
598.00000
783.00000

and airflow mode table goes like this

0 1 2 4 6 8 10 12 13 14 15 16------------>16

this all depends on your o2s, i think my stockers were better at oscillating than the densos are. if the o2s are oscillating very slowly, you want to take out fuel because it is using to much to switch above and below 14.63. if it hovers at the switch point and doesnt go high or low (doesnt oscillate) you need to raise the number.

GuitsBoy

iTrader: (4)

DENSOs???!!!??? Did you say DENSOs?!?!?!? Ive got denso's too and i have to say I wish i had just stuck with stock or bosch o2s. I wonder how many bucking cars are running densos.

Ragtop 99

iTrader: (7)

This sounds very helpful, but can we dumb this down for the masses?

I understand that the mode comes from "Mode vs Airflow" table which converts airflow to a number between 1 and 16. Are the units of measurement here the O2 sensor voltage? Can you elaborate a little more on what moving the numbers lower does?

Basically the idea here is to create cells (i.e. Modes) where we are having problems for fine tuning. I notice that for a 1999 PCM, other tables use only even numbers. Should we try to use even numbers in the problem zones?

Can you explain the units of measurement and elaborate on why this works?



Thanks for your patience and time

GuitsBoy

iTrader: (4)

Ragtop, like I said, this is definately a work in progress.

As for the o2 switchpoints, i chose to lower the first two cels to try and lean out my idle. The rest I simply made a gradual increase to gradually richen the switchpoints as load increases. The numbers here are in sensor mV. Anything above .xxx V is considered rich and the PCM pull fuel, anything below .xxx V is considered lean and the PCM adds fuel. How much fuel it adds is up to the proportional tables.

As for the airflow modes, odd or ven numbers shouldnt matter. You were right in that its to try and create more modes across the problem areas and that the added resolution should help us fine tune.

As for the Closed Loop prop base vs. airflow mode table, i dont know if these numbers are units of measurement. I think theyre just a base number that gets multiplied by the numbers in the "o2 error" table and eventually gives the computer a final "gain" value of how much fuel to add or subtract as the o2's swing.

Im interested in WS6FirebirdTA00 values in this table. setting it as low as 4 is almost disabling proportional fueling in those cells. I would think this would give a similar effect to running in open loop at idle and low load cells. Depending on the accuracy of your VE table, running open loop can either help or hurt you in terms of bucking.

If nothing else Im glad to hear some other people comment on prop fueling as a possible means to get rid of this god awful bucking that plagues our cammed cars.

GuitsBoy

iTrader: (4)

WS6FirebirdTA00 - What do your o2 error tables look like? I lowered mine a bit, but maybe ill bump them up to stock and try your ultra low prop fuel numbers.

bowtieman81

iTrader: (35)

Hmmm, guitsboy and I are chasing the same thing. Very interested to see how your endeavor turns out. I would play with it myself but my laptop has been taken back by it's orginal owner (wife) temporarily.

PS, I have stock corvette Bosch O2 sensors, so we can't blame the densos.

WS6FirebirdTA00

iTrader: (33)

i think my gm o2s oscillated a lot better and heated up a lot faster. on start up stock o2s would not get the STFT above +9 when they were cold. the densos get up to +16. once they are nice and hot its not so bad but i still think they oscillated a lot slower.

i left all the other tables stock. i hooked up a WB and the switch points were prefect because my ve was barely off with tuning it from the o2s. if you have hp tuners log those things i said and you can shoot me an email. make sure you have no more than 24 pids logging or else it will make it look like the oscillation is fine because the sample rate is slower. of course there will still be bucking from a lazy o2, when i take a look at the o2 readings during bucking, they went way rich or way lean on me. but most of this was when getting back on the throttle. make sure the car is warmed up when you do this and in normal FTC ie 1-19 and not still in warm up phase. budchevy358@yahoo.com is my email. id like to see how this works out. i know there are a lot of guys without bucking but even with identical cams and looking over their tunes, they did nothing more than i did to control it. i think it just depends on the car and how moody it is, we all know that some just dont like to behave . i am tempted to buy stock vette rear o2s and put them on and see what happens. thing is, i had a set of 38# injectors on my car that wouldnt work out even with the cam, and put them on my friends 99 SS with z06 cam and there is no problem. i tuned his car as well and put the same settings in his car as mine. another thing that helped that was recommened to me was to turn of LTFT. once the VE is close enough i would say turn them off. then you dont have weird numbers remembered. my car tamed out a bit when i did this as well