Ethanol questions - converting non-flex fuel to ethanol

[the_red_shark]

A flex fuel OS without the sensor works by looking at the trims over some period of time, I'm not sure of the details.

Without the intank sensor your ecu has no idea the mix of fuel that is actually going into your engine. All it knows is stoich mixture is 1 lamda. So when tuning you see lamda 1 or 14.76 on your wideband gauge, its actually showing you the stoich mixture of whatever fuel you are using.

So by my understanding you really don't tune it any differently than you tune gas. Cruise at 1 (14.7), and WOT say 11.7 (very rough example to show a point), so your thinking doesn't need to change. Which leads me to the point that any ethanol tables are irrelevant to any vehicle without a flex fuel sensor.

[Chevy366]

The thing with E85 is to run it you have supply more fuel. E85 motors have larger injectors, while you can tune a non-flex-fuel to run E85.
Here is some more; http://forum.efilive.com/showthread....&highlight=E85
Do a site search "E85" there is a lot of info here on it.

[BLK02WS6]

Without the intank sensor your ecu has no idea the mix of fuel that is actually going into your engine. All it knows is stoich mixture is 1 lamda. So when tuning you see lamda 1 or 14.76 on your wideband gauge, its actually showing you the stoich mixture of whatever fuel you are using.

So by my understanding you really don't tune it any differently than you tune gas. Cruise at 1 (14.7), and WOT say 11.7 (very rough example to show a point), so your thinking doesn't need to change. Which leads me to the point that any ethanol tables are irrelevant to any vehicle without a flex fuel sensor.

I don't think what you are saying about the ethanol tables being irrelevant is true. From the research I have been able to do, it appears that they have the PCM set up so that it drives the tune to the ethanol tables based on O2 feedback or something - but I can't figure out the details - one guy was talking about the sign wave that the O2 sensors makes changes... maybe because of the ethanol burning cooler? I don't know and was hoping one of the experts on here knew how it works...

I agree about lambda being lambda no matter which fuel you run - but the calculation to get AFR is where the difference comes in. 1 lambda is 14.76 with gas, but not with ethanol - it is 9.76... Maybe that is how they get the PCM to force into the ethanol tables... If the PCM sees 1 lambda from the O2 sensors, when ethanol is in the tank, it will take more fuel to maintain 1 lambda - maybe that's how it knows...

I know for sure that some year model flex fuel vehicles don't use a sensor in the tank...

If I end up going to ethanol, I really want to be able to run both fuels from the same tune - not have to flash a different tune in order to switch. And not have to run the tank down to empty either...

[BLK02WS6]

Here is a writeup I found on the Virtual Flex Fuel Sensor - this was for the 2006 Impala, but the theory would be the same for any flex fuel vehicle that doesn't have a sensor...

"In the past, GM had some small trucks and SUVs that could operate on different mixtures of ethanol-based fuels. These vehicles used a fuel sensor in the fuel line that signalled the computer how much ethanol was present in the fuel; the computer would add or subtract the amount of additional fuel required. Now, the Impala flex fuel system can perform this analysis without using any additional sensors. GM has developed a Virtual Flex Fuel Sensor (V-FFS) software program that calculates the ethanol content in the fuel, instead of using a sensor to measure it. When the fuel level in the tank increases as the vehicle is refueled, the computer recalculates the percentage of ethanol in the fuel and automatically changes the air/fuel ratio. To do this, the computer temporarily stops the operation of other emission systems and monitors the oxygen sensors to determine ethanol content. The test is done several times until calculations remain stable. This can take several minutes when the engine is idling, but much less time at higher fuel flow rates."

and another I found:

"For 2006 and 2007 models, E85 compatible vehicles marketed in North America no longer use an alcohol sensor to determine and adjust for the alcohol content of the fuel in the tank. Instead, the vehicle "learns" (calculates) the alcohol content of the fuel, (and subsequent mixture in the fuel tank), through a series of measured adjustments.

Adjustments

After the re-fueling event, the system registers the amount of fuel that was taken on-board, relative to the amount that was in the tank. Reading fuel trim and O2 sensor activity, the system determines the ethanol content of the fuel that was added. Based on that determination, it adjusts itself to the expected alcohol mix in the fuel tank and lets the fuel trim and O2 sensor activity fine tune the adjustments. The system must remain in closed loop in order for this adjustment to occur. Numerous short trips after switching from gasoline to E85, or vice versa, can result in driveability symptoms due to the inability of the system to adjust for fuel composition (by not attaining the parameters necessary to reach closed loop operation). "

[the_red_shark]

I don't think what you are saying about the ethanol tables being irrelevant is true. From the research I have been able to do, it appears that they have the PCM set up so that it drives the tune to the ethanol tables based on O2 feedback or something - but I can't figure out the details - one guy was talking about the sign wave that the O2 sensors makes changes... maybe because of the ethanol burning cooler? I don't know and was hoping one of the experts on here knew how it works...

I agree about lambda being lambda no matter which fuel you run - but the calculation to get AFR is where the difference comes in. 1 lambda is 14.76 with gas, but not with ethanol - it is 9.76... Maybe that is how they get the PCM to force into the ethanol tables... If the PCM sees 1 lambda from the O2 sensors, when ethanol is in the tank, it will take more fuel to maintain 1 lambda - maybe that's how it knows...

I know for sure that some year model flex fuel vehicles don't use a sensor in the tank...

If I end up going to ethanol, I really want to be able to run both fuels from the same tune - not have to flash a different tune in order to switch. And not have to run the tank down to empty either...

If you look in the description of the tables it's explains it better. If the ethanol blending it is commanded to run off the ethanol tables, whereas if it isn't runs off the normal fueling tables and you tune to suit.

Your o2s don't know what fuel is in the car they read the mixture and adjust trims. The ecu based off what you command is no different from ulp to e85, lambda is 1 so let's say your Stoich value on ulp is 1 you will require a richer mixture on e85 so whilst your wb reads lambda 1 your fuelling is up say 30% for example to achieve that.

By my thinking, and I'm very happy to be corrected as I'm always looking for ways to improve, flex fuel cars without the intank sensor would work in a fashion that the o2s would sense the lean mix and assume an ethanol fuel was being used and adjust trims heavily to compensate, how this would be represented in the tune I am not sure.

[Chevy366]

Here is a writeup I found on the Virtual Flex Fuel Sensor - this was for the 2006 Impala, but the theory would be the same for any flex fuel vehicle that doesn't have a sensor...

"In the past, GM had some small trucks and SUVs that could operate on different mixtures of ethanol-based fuels. These vehicles used a fuel sensor in the fuel line that signalled the computer how much ethanol was present in the fuel; the computer would add or subtract the amount of additional fuel required. Now, the Impala flex fuel system can perform this analysis without using any additional sensors. GM has developed a Virtual Flex Fuel Sensor (V-FFS) software program that calculates the ethanol content in the fuel, instead of using a sensor to measure it. When the fuel level in the tank increases as the vehicle is refueled, the computer recalculates the percentage of ethanol in the fuel and automatically changes the air/fuel ratio. To do this, the computer temporarily stops the operation of other emission systems and monitors the oxygen sensors to determine ethanol content. The test is done several times until calculations remain stable. This can take several minutes when the engine is idling, but much less time at higher fuel flow rates."

and another I found:

"For 2006 and 2007 models, E85 compatible vehicles marketed in North America no longer use an alcohol sensor to determine and adjust for the alcohol content of the fuel in the tank. Instead, the vehicle "learns" (calculates) the alcohol content of the fuel, (and subsequent mixture in the fuel tank), through a series of measured adjustments.

Adjustments

After the re-fueling event, the system registers the amount of fuel that was taken on-board, relative to the amount that was in the tank. Reading fuel trim and O2 sensor activity, the system determines the ethanol content of the fuel that was added. Based on that determination, it adjusts itself to the expected alcohol mix in the fuel tank and lets the fuel trim and O2 sensor activity fine tune the adjustments. The system must remain in closed loop in order for this adjustment to occur. Numerous short trips after switching from gasoline to E85, or vice versa, can result in driveability symptoms due to the inability of the system to adjust for fuel composition (by not attaining the parameters necessary to reach closed loop operation). "

Have not tested it, but a non-module flex fuel OS should work as long as it is for the year and body of the vehicle, the only problem would be the injectors they are definitely larger in a Flex Fuel engine. I would assume the refuel event is handled by the ECU.
There are some 20 plus tables that are different in a Flex Fuel tune versus a non FF tune. I have posted on a 5.3L the differences somewhere on the site. It looked as thought the EQ table (EQ table has a sliding scale based on the determined percentage Ethanol content, thus commanding the correct EQ/AFR) was the determining factor ie 14.76 versus 9.76. There was minimal change in the VE, MAF and timing tables.

Something I found;
In 2006 GM changed the way ethanol percentage of fuel was calculated by their trucks. This new system was deemed Virtual Flex Fuel System. Instead of using an additional sensor in order to measure ethanol content, the ECM had a software upgrade which allowed it to make this measurement by utilizing the fuel tank pressure sensor and level sensor signals. At a key on event the ECM looks to see if the fuel tank level sensor signals atleast a 2 gallon change from the last key off. If so, the ECM shuts the tank vent solenoid, monitors the fuel level and fuel tank pressure. These readings are applied to a formula which gives an ethanol percentage. The commanded air/fuel ratio is then changed according to ethanol percentage of the fuel.


In 2006 GM trucks used the same 160 pin ECM with blue and green terminal position assurances as did the 2002-2005 trucks.

[BLK02WS6]

Yeah, it appears the injectors would be my problem - would have thought they would all use the same for cost reasons, but flex fuel are bigger. I would think my stock ones could come close to supporting E85 since the engine is totally stock, but if that were true, they would have done it that way...

The price spread of regular gas over E85 around here has not reached a point where it is worth it yet - but if something crazy happens and gas goes through the roof, I wanted to know if I could do it by simply flashing in a new OS... I would still be tempted to put my injector tables into the flex fuel OS and try it on E85 to see how far it is off... I would put in half a tank only so I would have room to put gas in if the injectors run out early. I'm thinking if you didn't run the crap out of it, the injectors would handle normal driving. Would be nice to have that flexibility if the world goes Mad Max one day and gas is $10 a gallon LOL!


Edit: looked up the fuel pump and it is different for the flex model too... just got even more expensive to do it... oh well, at least I know now and understand a little more how it works!

[driver456]

I didn't read through the whole thread,But here's what I did to my 99 Silverado with a 0411 pcm.I hooked up the ethanol sensor and full flashed a flex fuel tune in,Works pretty good.I tuned the truck 1st on a full tank of pump gas.I hooked up the scanner a few times and you can see the comm.fuel change on what ever % the ethanol was,But my a/f gauge always reads the same no matter what % of ethanol I have in there.Now I don't have to worry about changing tunes

[driver456]

Towing my car to the track,I used 5 gallons more fuel with 65% ethanol compared to to 10 or 15%

[Chevy366]

Towing my car to the track,I used 5 gallons more fuel with 65% ethanol compared to to 10 or 15%

So you left stock injectors? I have read that the stock injectors will work fine. Did not know about the fuel pump, what is the difference there?
At the beginning of E85 people said they just filled up with it and off they went with no problems. Some did have to change fuel filter (became clogged due to tarnish in the tank and lines turning lose) and that was about it.
The 5.3L tune I showed as a comparison I had to hand change all tables because we can't compare different OS tunes, so I found and copied all tables to a like tune so as to be able to show differences(PITA).