iamdub
Full Access Member
They can't exceed 10% as this could cause damage to non-FlexFuel vehicles, or at least lead to poor operation. I'd say the ~30% calculation in alcohol content is an error on your Tahoe's part.
Ethanol percentage flex fuel
- Thread starter wsteele
- Start date
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They can't exceed 10% as this could cause damage to non-FlexFuel vehicles, or at least lead to poor operation. I'd say the ~30% calculation in alcohol content is an error on your Tahoe's part.
iamdub
Full Access Member
Does this tell you anything, compared to your driving and diagnostics procedures?
"E85 Flex Fuel Description
E85 compatible vehicles no longer use an alcohol sensor to determine and adjust for the alcohol content of the fuel in the tank. Instead, the vehicle calculates the alcohol content of the fuel through measured adjustments.
The ethanol calculation occurs with the engine running after a refueling event has been detected via a measured change in the fuel level sender output. The virtual flex fuel sensor (V-FFS) algorithm temporarily closes the canister purge valve for a few seconds and monitors information from the closed loop fuel trim system to calculate the ethanol content. This logic executes several times until the ethanol calculation is deemed to be stable. This may take several minutes under low fuel flow conditions such as idle, or a shorter time during higher fuel flow, off-idle conditions.
Air-fuel ratios and the corresponding ethanol percentage are updated following each purge-off sequence. The fuel alcohol content percentage value can be read on a scan tool.
When an E85 compatible vehicle is built, an ECM or PCM replaced, or if the learned alcohol content has been reset with a scan tool the fuel system will need to contain ASTM gasoline with 10 percent or less ethanol content.
A minimum of 11 liters (3 gallons) must be put in the tank in order for the vehicle to recognize a re-fueling event. It is not necessary to turn the ignition OFF in order to have the re-fueling event recognized, however local safety regulations should be followed.
After the re-fueling event, the system registers the amount of fuel that was added, relative to the amount that was in the tank. Reading fuel trim and O2 sensor activity, the system determines if the fuel added was either ASTM Gasoline or ASTM E85. Based on that determination, the system adjusts to the expected alcohol mix in the fuel tank, and then the fuel trim and O2 sensor activity fine tunes 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 E85 to gasoline, can result in drivability symptoms due to the inability of the system to adjust for fuel composition by not attaining closed loop"
That was my assumption. @Fless had posted a similar test kit on the other thread that had morphed into the Ethanol percentage quest. I hadn’t bought one as my assumption was Costco wouldn’t risk a major lawsuit for a few cents a gallon in added profit. I think I will go ahead and check it anyway, just for my edification.
That is very helpful, thank you. I am obviously still puzzled as my assumption the old O2 sensors were the likely source of the error, clearly didn’t pan out. But at least my guesses as to how the thing worked weren’t too far off.
They have released new calibrations to fix calculation errors, but unfortunately my truck has the latest calibration for my VIN (thanks again to @Fless for that help), so I a, back to square one at this point.
After the content test, I think I will try other gas brands and see if things move around.
One thing I have noticed is my truck never completes its evap monitor. I am wondering if that inability to complete that monitor has anything to do with the likely Ethanol miscalculation it is producing.
I am pretty sure at this point the system works to some degree, as with the 0% 76, it didn’t budge from the 3% the Tech 2 reset it to for the whole tank of gas.
I think you might be on to something with your comment about the evap monitor not completing. With what @iamdub posted about the canister purge valve needing to be closed for a few seconds while the info is monitored, perhaps there is something going on (or not) with the evap system.
I am going to see if I can exercise (test) the canister purge valve with the Tech 2. I would like to get to the bottom of the evap monitor never completing in any case, although I have read many say their's never completes.
swathdiver
Full Access Member
There are several Sunoco stations in my county that sell different levels of ethanol and despite what the stickers say, you never know what you're going to get! That's even taking into consideration how it will mix with the remaining fuel on board. The Racetrac that sells E85, is much more consistent.
E85 can be anywhere from 51% to 83% (the last two percent are chemicals to make the fuel inedible)
E70 is a winter blend E85, 51% to 70%
I have also seen pumps advertising E15/88, E20, E25, E30
Sunoco also sells E85R - 85% and is considered an off-road racing gas
I suspect that Bill's station might be selling fuel that is not what it appears to be. Best way to tell is to fill up one of them vials and see. I have one, can fill it right off my fuel rail.
E85 can be anywhere from 51% to 83% (the last two percent are chemicals to make the fuel inedible)
E70 is a winter blend E85, 51% to 70%
I have also seen pumps advertising E15/88, E20, E25, E30
Sunoco also sells E85R - 85% and is considered an off-road racing gas
I suspect that Bill's station might be selling fuel that is not what it appears to be. Best way to tell is to fill up one of them vials and see. I have one, can fill it right off my fuel rail.
I like the idea of testing from the fuel rail for a comparison to the Tech 2 reading, but that's not going to be a direct measurement of what's coming from the pump. I think @wsteele would like to confirm the efficacy of the supply so he can move on down the diagnostic path. (I used "efficacy" since it's all I hear about the 'rona shots...)
swathdiver
Full Access Member
I get it, was just explaining the set up I have. If I were going to fill that little beaker up a the gas station, I would surely spill more on the ground that goes into the little bottle. It'll evaporate quick enough though but sure would stink up my hands unless wearing gloves. I got it, pump some into a bowl and then submerge the beaker in that to get a sample. Yeah, that'll work.
I bought this one off ebay, the numbers are etched into the glass, no sticker.
I bought the test bottle James recommend above. I liked the idea of etched graduations.
I had a plan already worked out to obtain without spills the test samples. I will get that done in the next week or so. My guess right now is Costco is probably selling legal gas and it is something my Yukon is doing in error that miscalculates the Ethanol percentage.
One primary reason for that conclusion is how rich my engine runs just after I do a cold start and it is running open loop. I think it is starting it extra rich because it thinks it has a lot of Ethanol, then cleans things up once it switches to closed loop. If the gas actually had the Ethanol the PCM thinks it does, that rich mixture would be closer to the mark starting out.
We shall see. I am also going to sit down with the Tech 2 and see if I can figure out how to command the Cannister Purge Valve and see if it is responding like @iamdub's write up says when calculating the % after fill up. Or maybe I will just stumble on why my evap monitor won't complete...
I had a plan already worked out to obtain without spills the test samples. I will get that done in the next week or so. My guess right now is Costco is probably selling legal gas and it is something my Yukon is doing in error that miscalculates the Ethanol percentage.
One primary reason for that conclusion is how rich my engine runs just after I do a cold start and it is running open loop. I think it is starting it extra rich because it thinks it has a lot of Ethanol, then cleans things up once it switches to closed loop. If the gas actually had the Ethanol the PCM thinks it does, that rich mixture would be closer to the mark starting out.
We shall see. I am also going to sit down with the Tech 2 and see if I can figure out how to command the Cannister Purge Valve and see if it is responding like @iamdub's write up says when calculating the % after fill up. Or maybe I will just stumble on why my evap monitor won't complete...
