E85Forum.com

Boosted3Bar · Joined: 14 Jul 2006 Posts: 50 Location: San Antonio, TX

[quote="hotrod"]
No! Not if your running 100% E85.

The Desired AFR as you defined it is the stochiometric fuel air ratio for the fuel being used.[/quote]

I think I confused you a little with how I worded the "desired a/f ratio" thing. The pcm in my car needs to know what a/f ratio it is supposed to be aiming for while in closed loop, that is what I mean by desired a/f. This what it tries to achieve with the fuel trims. That a/f number is based on the factory narrow band o2 sensor. For this part I'm not at all concerned with the wideband sensor that is mounted some place else and not connected to my vehicle's computer at all.

The way I was thinking this works is since the factory o2 sensor is just reading lambda and my pcm is converting that into an a/f ratio number based on the assumption that it is burning gasoline, if I switch to E85 the o2 sensor is still reading lambda but the pcm is still assuming I'm burning gasoline. So let's say .480 volts out of the o2 sensor equals 1 lambda on gasoline, and the computer assumes .480 volts equals 14.7. When I switch to E85 1 lambda should theoretically still equal ~.480 volts right? I hope I'm correct so far because I feel like I'm really starting to understand this part, lol. So my pcm will see that .480 volts with the E85 and it'll assume I'm running 14.7:1 because it doesn't know that I switched fuels. I really hope this makes sense, my communication skills on the internet are way below average. The only reason I have to use a ratio is because the computer does not understand lambda.

For open loop and WOT tuning I will be using my wideband and lambda, but for closed loop I have to specify a target a/f number that is based off of the factory o2 sensor.

I hope this is more clear and makes sense. I read that article, very informative, thank you. I appreciate all of your efforts in helping me understand these "should be very basic" concepts.
_________________
2003 Grand Prix GTP

http://www.cardomain.com/ride/2155875

hotrod · Joined: 19 Apr 2005 Posts: 872 Location: Colorado

I would assume you want to put in the gasoline AFR you want to hit for stochiometric combustion then for closed loop to minimize emissions they target perfect combustion.

The only way to know for sure is to do some tests and see what happens. I would probably start with plain gasoline, and then add a known percentage of E85 without changing any parameters and see how your mixture changes. If closed loop stays the same as you add more ethanol then your narrowband O2 is doing its job of adjusting fuel trims to stochiometric combustion.

Larry

jachristner · Joined: 12 Oct 2005 Posts: 64 Location: Kokomo, IN

I'm running 25% ethanol in my 1992 Cavalier. Quite often, almost always when at low speed or stopped, I'll notice the smell of alcohol. This has happened even with all the windows up. Has anyone else experienced this? Is it just the nature of the fuel or something I should be worried about? I haven't noticed any fuel leaks anywhere and I don't smell fuel when the tank is full of 100% gasoline.

Alcohol · Joined: 17 Apr 2007 Posts: 634 Location: Central Wisconsin

jachristner · Joined: 12 Oct 2005 Posts: 64 Location: Kokomo, IN

I've noticed it after the engine is fully warm. I think I have a loose exhaust connection somewhere because I hear a rattling from under the car. Perhaps that has something to do with it.