Great question, since they are ALL flex fuel anyway!
What is really interesting are goofy spark number for the few flex fuel vehicles out there when they run E-85. If I didn't know better, it is as if they are intentionally looking for bad mileage.
Originally Posted by laser_racer
Sam Michael
Chemical/Controls Engineer
Based upon what I'm reading, it sounds like all I need do is tune my car with gas; then change my stoich based on AFR/fuel trim error when using an ethanol blend. Of course that would be a pain if you had to manually change it for every tank full, but if you kept your mixture the same and got your fuel from the same place you may only need to check it from time-to-time.
Bunch of misinformation in this thread guys.
GM started out with an actual sensor for flex fuel vehicles. Later they went to an ECM based "virtual" sensor. Late model engines are going back to an actual sensor. This quote I'm pasting here is from a 2012 Buick Regal with a 2.0L LHU motor. It has an actual sensor.
You can't turn a non flex fuel vehicle into a flex fuel vehicle by simply changing a few things in software. There are many other differences, mostly bigger injectors and fuel pumps. You can run a percentage of Ethanol in ANY car, it's just a matter of how much E there is and how far the ECM can compensate.
There is NO WAY IN H#LL that GM, or any other car company would tune for bad mileage. They try to optimize the spark in the flex fuel tables as best they can, but obviously have to be VERY conservative not knowing what fuel blends or qualities will be used in that motor for the next 5 or 10 years they have to cover any problems for.
On current design motors (low compression compared to what would be ideal for running E85 100% of the time) you aren't going to GAIN mpg's by running E85. Sorry but it's not possible. That's fact. If you run between 30 to about 40% Ethanol, and optimize ign timing perfectly, you CAN gain mpg's over straight gas. An Ethanol blend beyond that and you'll be loosing too much efficiency. All of these things I'm claiming can be verified if you do a little web searching. There have been many studies done on Ethanol mixes and mpg's, a few even used the LNF motor for testing. I've been running an Ethanol mix for quite a while now, fwiw, I'm getting about 25mpg average out of a 500+hp LNF running an E47 mix.
Flex Fuel Sensor
The flex fuel sensor measures the ethanol-gasoline ratio of the fuel being used in a flexible fuel vehicle. Flexible fuel vehicles can be operated with a blend of ethanol and gasoline, up to 85 percent ethanol. In order to adjust the ignition timing and the fuel quantity to be injected, the engine management system requires information about the percentage of ethanol in the fuel.
The flex fuel sensor uses quick-connect style fuel connections, an incoming fuel connection, and an outgoing fuel connection. All fuel passes through the flex fuel sensor before continuing on to the fuel rail. The flex fuel sensor measures two different fuel related parameters, and sends an electrical signal to the engine control module (ECM) to indicate ethanol percentage, and fuel temperature.
The flex fuel sensor has a three-wire electrical harness connector. The three wires provide a ground circuit, a power source, and a signal output to the ECM. The power source is battery positive voltage and the ground circuit connects to an engine ground. The signal circuit carries both the ethanol percentage and fuel temperature within the same signal, on the same wire.
The flex fuel sensor uses a microprocessor inside the sensor to measure the ethanol percentage and fuel temperature, and changes the output signal accordingly. The electrical characteristic of the flex fuel sensor signal is a square-wave digital signal. The signal is both variable frequency and variable pulse width. The frequency of the signal indicates the ethanol percentage, and the pulse width indicates the fuel temperature. The ECM provides an internal pull-up to 5 V on the signal circuit, and the flex fuel sensor pulls the 5 V to ground in pulses. The output frequency is linear to the percentage of ethanol content in the fuel. The normal range of operating frequency is between 50 and 150 Hz, with 50 Hz representing 0 percent ethanol, and 150 Hz representing 100 percent ethanol. The normal pulse width range of the digital pulses is between 1 and 5 ms, with 1 ms representing −40°C (−40°F), and 5 ms representing 151.25°C (304.25°F).
The microprocessor inside the sensor is capable of a certain amount of self-diagnosis. An output frequency of 180 Hz indicates either that the fuel is contaminated, or that an internal sensor electrical fault has been detected. Certain substances dissolved in the fuel can cause the fuel to be contaminated, raising the output frequency higher than the actual ethanol percentage should indicate. Examples of these substances include water, sodium chloride (salt), and methanol.
It should be noted that it is likely that the flex fuel sensor will indicate a slightly lower ethanol percentage than what is advertised at the fueling station. This is not a fault of the sensor. The reason has to do with government requirements for alcohol-based motor fuels. Government regulations require that alcohol intended for use as motor fuel be denatured. This means that 100 percent pure ethanol is first denatured with approximately 4½ percent gasoline, before being mixed with anything else. When an ethanol gasoline mixture is advertised as E85, the 85 percent ethanol was denatured before being blended with gasoline, meaning an advertised E85 fuel contains only about 81 percent ethanol. The flex fuel sensor measures the actual percentage of ethanol in the fuel.
See I knew I wasn't a crazy person lol.
so is it doable or not given a reasonable amount of dead presidents?
I'm going to test my theory on my car, I had an E85 mix in my car before and my fuel trims were about 10% lean, so If I add 10% to my stoich I get about 13.2 which according to a flex-fuel vehicle is about 25% ethanol, which is what I mixed it as. So in theory if I change my stoich in my tune to this, and since most values are in lambda my resulting fueling should also be richer. As I said before this would be strictly a manual operation, everytime time you fill up check you trims and adjust stoich in your tune accordingly.
In case anyone is interested this didn't exactly work as expected on my car, I set the stich based on AFR error in open-loop, check it again and it's still off by 5%, change it again by 5% and then it was richer than the mixture I had and HP dropped, and it was still showing 5% off.
Post #3 also
HP-Unlimited Tuning and Custom Fabrication
Houston area performance parts dealer
MD800 Mustang Dyno 713-560-3889 Taylor
2016 Camaro A8 "shop car" FIRST 6th GEN CAMARO OVER 200mph IN THE MILE 203.5mph
Why are you tuning in open loop? If that's how you want to do it you need custom pid and custom wideband so car doesnt see the current wideband reading 14.7 instead of 13.2.
Great minds must think a like silver lol.
It's difficult to convert a non-FF engine to FF because GM doesn't just disable one or two tables, often they screw up dozens of tables to make it difficult. This info given to me by an automotive engineer that used to convert vehicles to flex fuel for a living. That's where the sensor comes in real handy.
Yeah, I know, old thread, but just wanted to put this where someone else may benefit.
As a follow up to TownDrunk....
SamGM2 actually started the program that I finished regarding flexible fuel tuning. This one really came back from the dead!
Some vehicles will work just fine by just enabling the option that HPTuners provides, especially if they share an operating system or calibration with a vehicle that is already an FFV. Quick & simple. For others, there are several On/Off switches relating to ethanol that would prevent the fuel from relearning. HPTuners has the ability to access all those tables, but they require time to follow the calibration map and then provide the user with access to those tables.
Some examples that prevented relearns....
Relearn fuel in the event of a refill of XX gallons.... but the car only has a < XX gallon tank.
Relearn fuel after ____ seconds of ____ event
Relearn fuel for ____ seconds
Relearn fuel if ST fuel trims > ____
the list goes on. For the one that took us the longest to start learning, there were at least 10 on/off settings we had to put into the right range. Don't give up on this if you really want fuel choice!
Reply With Quote