hodge9386

I am doing some remote tuning for a friend of mine with a 2013 sierra flex fuel truck being done by a very reputable tuner and I noticed that his commanded afr is set to 13.7ish and 11.5ish at WOT and when I asked the tuner about it he said it was because the 20% alcohol the truck is reading in the fuel.
It got me to thinking about my trucks and vett that I have tuned which are all set to the normal 14.7 and 12.8ish at WOT verified by a wideband and the all run great and have been for a long time. Should I be running it richer for the ethanol that is now being put in our fuels? I know the sticker on the pumps say "may contain up to 10% alcohol" so should I adjust my tune for it? What about timing? I run them all at 26-27* at WOT.

aaronc7

You gotta think about things in term of lambda- that's all the O2 sensor (stock narrowband or aftermarket wideband) sees. Then it just multiplies that lambda value by whatever the pcm tells it to or what you tell it is stoich AFR. Generally you want cruise at 1.0 lambda and WOT/max power at 0.85 lambda = 14.7 and 12.5 for pure gas and how most devices are calibrated. Unless the pcm can tell what percent of the fuel is ethanol or you can tell it otherwise, most cars (and the C5 for sure) assume 14.7 stoich. So even if you were running E85 it would say 14.7 AFR or whatever at cruise.

Hope that makes sense, either way you're AFRs are spot on basically and in cruise/closed loop operation it's able to compensate for the 10% ethanol no problem.

tblu92

I don't know of any gas stations that have a gas 20% ethanol content----Are you sure the ower didn't put some mix of E85 into his tank ?? If his car is a flex fuel car from the factory the ECM should compensate for the added ethanol content
on it's own-- and adjust both the P/T fuel and the WOT fuel---as well as the timing--
The Stoich table in the tune already has a table that can self adjust from 0% ethanol all the way up to 80%

Johnny wangwang

12.8 IS Rich for all motor! For Boost you wanna be right at 12.0:1 or right under it for E85 or gas. 12.8 on boost with e85 is about the limit of what you can get away with power wise when in boost depending on your tune.

hodge9386

who said anything about boost? 12.8 is not rich for all motor.

so if i tuned it with a wideband at 14.7 and 12.8 WOT with the same fuel then it should be right anyway because the e10 was accounted for and the proper amount of fuel was already added?

hodge9386

and yes the tank was pure gasoline and it was reading 20%, the tuner said he has actually seen more than 20% from pump 93. i understand how the flex fuel can compensate for the added alcohol. what im not sure about is older cars that dont have a alcohol sensor.

aaronc7

correct