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flex fuel question

Flex Fuel Tuning

Discussion and questions related to the course Flex Fuel Tuning


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I think I figured it out how too tune flex fuel its better too tune map 1 pump gas and ingnition table 1 then copy everything from map1 too table 2 drain all the pump gas and install e85 then tune table 2 and ignition table 2 when your done with the tune then get the blend table set right

Yes Charles that's essentially the process. We do cover the exact steps of that process inside the course and you can also watch the worked example to see it being put to use.

Andre, does this course / example show how to create a variable flex fuel tune that infers ALC percentage based on Injector PW after a fuel change event, Then adjust Lamda and timing tables acordingly? Or is more for either or scenarios in which full pump, or full e85 is required.

The comercial tune I eventually want to replace does this. It is from Lund racing and it has been OK but I want to do my own eventually as I dont think thier tune matches my car that well. diffrent rpm ranges and loads have very diffrent ltft and stft behavior which seems like bad MAF scaling, or maybe bad injector data. I have been running it on roughly blended e50, which infers to 50-60 percent ALC. If I run the tune at pure e85 my car hates it, mushy throttle, pops, and dramatically diffrent exhuast sound.

Hi, I'm a new member here and haven't gotten a chance to look at the E85 course. I will chime in on the E85/Flex fuel issue though based on my own experience on the OEM side and aftermarket tunes.

For purposes of this discussion, there are 3 ways to do E85/ethanol tunes.

The first is to take an ECU (flashable stock ECU or standalone) that has software that was never designed/configured for E85 and just make it work. That's what a lot of advertised "flex fuel" Ethanol tunes do. They use the fuel trims/adaptives that were designed for E10 and adjust the basic fuel and spark calibrations so that it works "Good enough." It sounds like that's what you have going on in your ECU, correct? There's always going to be compromises. The ECU doesn't know what the actual ethanol concentration is because it doesn't have a sensor to detect it, nor does it have a model to do so in lieu of a sensor.

The second method is to calculate ethanol %. This is the most common method used in OEM flex fuel applications today. Each time you fill up, the software looks at the o2 sensors and calculates what is essentially a 3rd layer of fuel trims. So on top of short and long term fuel trim, you have calculated ethanol %. Using this value it will automatically scale injector pulsewidth, and can toggle "E85" and "E0" modes. Usually there is some kind of "Dead band" where say E0-E20 run similarly as one mode, and E70 to E100 run similarly as another mode, with linear interpolation between. This sensor-less flex fuel software is mostly found on stock ECUs for frumpy engines that nobody bothers to tune in the aftermarket. The OEMs only use it to get government fuel economy credit as cheaply as possible. It sounds like you are hoping for the flexibility of a system that can actually calculate Ethanol %. It's simply not possible unless your stock ECU was designed for it; it needs special code and ethanol models. Nobody in the aftermarket is writing ethanol models when you can just buy a sensor.

The third method is to directly measure ethanol content with an Ethanol sensor. You can do that through special code that the aftermarket adds to a stock ECU (basically hacking the stock ECU), where it takes the ethanol sensor as an input and automatically makes changes to injection. Cobb has a Flex fuel kit for an STi for example (EJ257 engine) that includes hacked ECU software and an additional sensor that is OEM grade. The OEMs used to use ethanol sensors in the early days but used a model to help get rid of them to save money, but good OEM grade sensors are widely available as a result.

If you are running a standalone ECU with flex fuel support they are also going to use an Ethanol sensor so that injection pulsewidth can automatically adjust. Directly measuring ethanol is much easier and more accurate than using fuel trims from o2 sensors. It's a relatively low cost item for someone tuning their project car.

So if your setup does not directly involve an Ethanol sensor it's highly likely that you will always be making compromises and noticing hiccups like what you have described. When someone tells you it's a "Flex fuel" tune, but there's no sensor and no custom code (like the Cobb kits) it means they are stretching the factory fueling algorithms and long term fuel trims that were only designed for E10.

sounds right, but I have never been able to identify why pure 85 runs like shit. I know guys from AEM and some others don't feel the stock 350 injectors are up for it, Lund disagrees but at this point I believe AED.

Livernois has also developed and sold a flexfuel tune for the 350. I know several people that scrapped Lund also and were actually happy with Livernois. Ken at Palm Beach Dyno once told me to avoid the FF tune, I should have listened but the torque improvements on the 5.2 with octane are hard to give up.

The further you get from whatever ethanol blend your quasi flex fuel tune was designed for, the more likely it will run poorly due to stretching fuel trims to the limit. The other thing to consider is the spark. Ethanol concentration affects combustion speed. If the ECU doesn't have real flex fuel code it's not going to be as good at adjusting spark across the whole blend range.

Keep in mind too that in a port injected engine, the unburned fuel collects in the port during cold start and any quick throttle movement. The wall film model accounts for this, but without true flex fuel code you don't have separate tip in fueling maps for E85. So the ECU can't compensate for all that extra fuel puddle in the port with a 1 size fits all calibration.

The flex fuel course doesn't currently cover the scenario where the ECU works out ethanol content based on fuel trim behaviour. We're assuming either a factory ECU or aftermarket ECU that's equipped with a fuel composition sensor to directly measure the alcohol content.

for a couple hundred bucks I think I will buy a sensor.