LSonederfull

I want to know how far off 02's read with off road y, med.cam size, etc.
Pcm is programmed for 14.7 to 1 but i feel o2's read incorrectly from slight missfires, low to no backpressure. I changed my stoich. setting to 14.9 to 1(small change) with the feeling that car has been running rich to maintain 14.7 on skewed 02's readings. Car feels crisper and better load transitioning performance. My question is how far off is pcm fueling with skewed o2' readings? Anyone play with Stoich specs to find out if this is the case?

LSonederfull

FWIW i have had no audible knocking or pinging, and wot seems to like this tune change.

txhorns281

iTrader: (12)

well, since we know O2s don't have a wide range of accuracy, the further you get away from stoich, the worse job the O2s do of keeping you there. Wideband sensors are more practical for dialing in AFRs beyond stoich operation. And you will also want to run Open Loop since in Closed loop the O2s cannot provide you reliability with any other AFR than stoich.

LSonederfull

Well my tuning is real close and has been wideband tuned on dyno, this is great for wot tuning. Admittadly Slowhawk has done a great job of overall tuning my car, but i feel car drives with a rich tendancy part throttle range of driving, and i was looking for basic method of changing this. Fuel mileage should show if i am on right track.

txhorns281

iTrader: (12)

You may have lucked out with a particular setting but generally you don't change stoich unless you change the type of fuel you are running. Just as you're kinda shooting in the dark, so will your car... Running anything other than stoich in closed loop is like taking away your PCMs ability to correct. There are other ways to resolve rich issues in part thorttle driving that retain stoich operation, and don't disturb other fueling tables.

LSonederfull

My strategy is that since pcm will compensate for almost all changes made to fueling outside of PE, than how about slightly changing what pcm is trying to maintain. I am interested in any input on peoples confirmation of rich idle/part throttle running caused by inaccurately read "lean condition". In other words does cam missfires cause false rich run condition? I am persuing this because of the o2's tendancy to carbon up and lose active switching that stock Ls1 enjoys. Dtc p1133 in particular. Does this help show where im going with this?

LSonederfull

Anyone played with this?

txhorns281

iTrader: (12)

High Overlap causes false AFR reading by your sensors. Raw fuel and air potential get jetted through the exhaust during the overlap period and contaminate AFR sensing. Even at stoich this can be a problem. Use a wideband for more reliability (though not much), and do the best you can. And it's like i said before, the further you push your O2s away from stoich, the harder it is for them to compensate, even if just a little bit. THEY ARE VERY INACCURATE DEVICES!

LSonederfull

Thanks for your comments, i understand and am sure you are right. My question to you is since i have atap/Edit tuning for idle/cruise, and Wideband/Dynojet tuning for WOT, how would you go about tuning for cleaner daily driving(better 02 switching?) I havent felt a negative side effect to my tweaking so far, even at wot driving, i plan on pulling some spark plugs soon to verify no light detonation and cleaner running.

txhorns281

iTrader: (12)

well if you like the way it feels, then that's up to you. Chances are you probably aren't going to hurt anything with what you've done, but as far as verifying that things are in order, you are sort of limited by the performance of your o2s (which we've already said sucks even at stoich). With a wideband, you can still be given BS readings, but at least beyond stoich it will be much closer that what your o2s might think. If you really want to tune an AFR outside of stoich range, create an open loop tune and fix your VE to produce what is commanded of it. But since your O2s can't really help you stay at your desired AFR in this scenario, YOU as the tuner must constantly update the tune. This would require lots of time, and probably and onboard wdideband setup. It's really up to you. If you're using o2s, just stay at stoich for as little problems as possible, if you want to run open loop, then be ready to change your tune daily

For the best driveability, just make sure your VE transitions are smooth and that it produces what is commanded of it. Your closed loop fueling should adjust when needed for you, but most everything will be inline. If you have a non-stock MAF, either ditch it or recalibrate it. I'd even try to recalibrate a stock MAF, but that's just me. Or run open loop and test yourself as a tuner!

LSonederfull

I do run fully ported maf, descreened, but Slowhawk has recalibrated it thru tuning to sort out the mess this creates. I have no hiccups or glitches in the complete range of driving, so im satisfied with it. I definitely want to stay with closed loop,thanks again for your input.

SSpeedracer

iTrader: (8)

I was under the impression that changing stoichiometric value will not affect AFR at closed loop. You need to change the O2 switch points below 500mV.

HumpinSS

iTrader: (1)

Changing stiochs affects ALL fueling tables.


14.7/1.13=13.00
14.9/1.13=13.18

This could be in either the Pe vs. RPM table or the Open loop f/a table or any tables that would use a multiplier to arrive at a target commanded AFR

GC99TA

iTrader: (30)

I have seen that formula used before and I have a few questions about it. I understand that if your PE vs RPM multiplier value is 1.13, it is commanding the WOT mixture to be stioch (1) plus another .13 of that value, equaling a 13:1 A/F ratio. My question is, how does the PCM decide how much fuel is needed at WOT to equal stioch. so it can calculate the final value? Is it reading VE table to determine this? That seems pretty reasonable to me, but I thought I read on here that the VE table isn't used in PE mode? Please explain.

Also, if the above assumption is true (that the VE table is read at WOT to deterime how much fuel is needed at a particular RPM and MAP point) then this formula would only work if the VE table was accurate, correct? In other words, if your VE table is causing a rich condition (negative trims) at 5000 RPM, then your WOT A/F ratio is going to be richer than commanded, right?

Sorry, I'm fairly new to this and I'm just trying to see if I grasp the concept. I don't mean to highjack the thread, but hopefully I'm not the only one wondering about this.

LSonederfull

Changing stoich value will change A/F in closed loop, it changes pcm's goal for A/F ratio. I compensated for false enrichment that cam and lack of exhaust backpressure from off road y pipe and cat back exhaust causes.
I am leaning mixture to make idle/cruise cleaner and to promote o2 switching activity. My wot tune can afford slight leaning, so all around car feels better set at 14.9 to 1 A/F stoich. setting.

Slowhawk

iTrader: (12)

Sounds like you need a wideband 02 in the car.The stock 02's do a great job keeping A/F at 14.7-1 which I see on the wideband 02's in a few cars that we installed them in.So changing the target A/F up to 14.9 could make a slight change but not much at all.A change to say 15.5-1 would probly be felt more and can give you an idea how the leaner cruise,idle would feel like.

LSonederfull

Don, thanks for the input. Since you have tested cars with wideband, when they are set at 14.7pcm do they actually read rich on wideband? Im talking at idle and part throttle only.

Slowhawk

iTrader: (12)

Nope,they hit 14.7-1 almost perfectly.You'll find that the car will idle /cruise better with A/F set to 13 -13.5-1 A/F though.