Terry Burger

iTrader: (4)

Looks like it's set to 14.7:1 in a factory tune. What happens if I change that to 15.5:1? Could I then just add extra fuel for WOT needs, and enjoy better gas mileage around town?

HumpinSS

iTrader: (1)

LMAO gas prices must be really getting to you. I wouldnt change those stioch values the o2 sensors are MOST accruate at that value. Any deviation from there and you may actuall hurting yourself. Here is one thing to try




https://ls1tech.com/forums/showthrea...ght=boundaries

jimmyblue

iTrader: (11)

The O2s will still trim you back to 14.7:1 because that
is their switchpoint.

14.6xxx is the "chemical truth"; best not to mess it around.

Now, if you lowered the O2 pivot voltage (found in the
Fuel Control > Open & Closed Loop > O2 Rich / Lean vs
Airflow Mode tables, you could jack those down to low
voltages and bias things lean a bit. But you might run into
trouble if you put them below 300mV, which is right where
things would get interesting. Worth a try though; I did a
little of this to mine but stayed above 300mV so no big
fuel economy bonus as far as I've noticed.

WS6snake-eater

Would this help with the rich smell at idle for big cammed cars? I would also assume that it would allow for a smoother transition between low speeds and idle. Any thoughts on low map/rpm bucking? Perhaps some help could be seen there as well. I have changed my pivot points in mine but left the closed loop vs airmode to stock. I'm going to try and switch to your setting for that table as well, and see if I can keep from burning my eyes.

hellbents10

iTrader: (10)

Ve table below 1200 and a little more timing down there for a big cam, maybe there is some more good ideas too. Just a place to start.

WS6snake-eater

VE table is perfect...nailed down solid. I have been playing with timing, and things are definately getting better. Biggest concer right now is smell at idle. The car is perfectly drivable right now, it just smells to holly hell.

jimmyblue

iTrader: (11)

Big cammed cars will shoot a lot of raw gas right
through the valve overlap window; that can't be
entirely helped.

I adjusted the airflow mode points up a lot, so that
mode 14 was about highway cruise, 15 & 16 above it.
The stock settings have everything crowded way low.

The airflow mode & pivots I believe are meant to
model exhaust thermals and may be a useful "handle"
to deal with the depressed output at idle / low cruise
on header vehicles. But if it's dead not switching, the
threshold doesn't matter much....
for people with headers.

JeremyF

iTrader: (23)

AFAIK if the stoich value was altered then the trims will follow suit as well. You will have skewed your FT's to a new value. and they will be based upon that AFR(?).

MNR-0

In OZ I enabled lean cruise to deliver 15-16 stoich from 35mph and above. Result is an extra 60miles per tank and average consumption 13.5l/100km CITY DRIVING. On the freeway it dips down to 9l/100km.

slow

iTrader: (7)

us US guys aren't so lucky to have that feature enabled

Ryan

HumpinSS

iTrader: (1)

Here in the US we dont have the priveledge of lean cruise unless we throw the car into open loop and manually set those AFR's

Terry Burger

iTrader: (4)

I wish I had that option! What mv do your o2 sensors average when you're at the 15-16 stoich?


Thanks,
Terry

66ImpalaLT1

Stoich ratio should only be changed if you're running a fuel which has a different AFR for stoich. For example, 85% ethanol, or maybe propane.

Terry Burger

iTrader: (4)

My basic question was if I change it, will that cause the cars air fuel ratio to converge to that number. I've a couple of "no" and a couple of "yes" responses. I'm inclinded to believe the "no" people, but wouldn't mind any addl input someone might have.

What I really want is lean cruise mode. I wonder what it would take to enable that? A reflash of an export OS?

monodax

The other way of "setting" the A/F ratio that the VCM thinks it is seeing is by using a Wideband system with at least 2 WB Sensors and 2 Narrowband Outputs. With my TechEdge 2B0 you can pretty much set whatever A/F ratio you want your VCM to think is stochiometric. I am sure there is dual wideband setups to do the same which would be cheaper than buying 2 seperate wideband kits. You would also need to delete your stock O2 sensors and use Widebands in their place.

This to me is alot of overkill in my opinion to achieve a leaner burn rate during normal cruising. You may be able to get some sort of splitter for the single wideband setups to feed both O2 inputs on the stock VCM but I wouldn't just for safety as you would never know the readings on the header that the WB sensor was not connected too.

66ImpalaLT1

I believe if you change this value, the computer will attempt to run at the new value, but the ltrims will correct it back to stoich according to the sensors, which is 14.7 for unleaded gasoline.

Terry Burger

iTrader: (4)

Ah ok, so what if I move it to 16.0, and then also adjust the o2 sensor b1/b2 R/L vs. airflow mode to around 300 (or whatever cooresponds to 16.0:1).

gameover

the stoich value defines what a 1.0 equivalence ratio (F/a multiplier, number in the PE table etc.) is. and the ratio of air/fuel the PCM uses to calculate the fuel.

eg. a PE value of 1.1 means command 14.7/1.1 AFR whihc results in a certain amount of fuel. If you change the stoich value then you directly affect what the PCM uses for all the base fueling. You should only change it if you are running a different fuel. Dual/hybrid fuel capable vehicles (eg. most 2004 and later vehicles) will notice the stoich AFR is a table and the value is based on the fuel composition sensor output.

Chris...

BigPlanTransAm

stoich ratio is how many parts of air is need to burn 1 part of gasoline. if youre running at stoich then i dont see how running leaner than that would make a difference because all the fuel in the cylinder is being mated to an oxygen molecule and being burned anyway.(im not saying it doesnt, thats kind of my form of a question )
as someone said before, different fuels(nitromethane, propane, alcohol) all have different stoich ratios and i would assume that is wwhat the table is for. instead of getting really involved trying to tune for alcohol instead of gasoline, you could just tell it the stoich ratio of the new fuel and the computer would make all the calculations for you