swathdiver
Full Access Member
I suspect that a vacuum or exhaust leak can trigger a relearn because the fuel trims are upset by such.
Ethanol percentage flex fuel
- Thread starter wsteele
- Start date
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So far, the only condition that seems to trigger the relearn on my truck is filling the tank. After a fill-up, when I drive enough (like 10+ miles) it will settle on a number it likes. Then the next cold start seems to cause it to make a final decision and the number usually jumps quite a but from the last calc. It will then stay at that spot until the next fill.
Today, I had a second start and drive today, after the fill. It was a warm start, so I wonder of it even got to open loop. After I started the engine, it was displaying 19.38% (down a few percentage points from when I turned it off the first trip after the fill).
It will be interesting if it stays there or goes lower/higher when I do the cold start tomorrow.
OK, final update for this fill. The E% calc after the first cold start after a fill (I had two warm starts after the fill), the % is the same as the final calc after the second warm start, 19.38%. About 19% above what is actually in the tank. 
I changed the canister purge valve to a new OEM unit and also installed a new OE E85 gas cap and did get a monitor complete on the Evap, so it looks like the canister purge valve isn’t playing a role in the poor performance of the virtual ethanol sensor.
I am thinking I am not going to get to the bottom of this issue. Glad I got the Tech 2 to reset it to 3% when it gets up into the 30’s percentage range.
I changed the canister purge valve to a new OEM unit and also installed a new OE E85 gas cap and did get a monitor complete on the Evap, so it looks like the canister purge valve isn’t playing a role in the poor performance of the virtual ethanol sensor.
I am thinking I am not going to get to the bottom of this issue. Glad I got the Tech 2 to reset it to 3% when it gets up into the 30’s percentage range.
Is the calculated ethanol percentage something one can monitor using a Bluetooth dongle and one of the Android apps? If so, which apps, and would it require buying the enhanced PIDs version (vs. the free version)?
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Yes, I am using a simple ELM327 Bluetooth dongle (like $20) and a free app called Car Scanner. The dongle is sold by Viecar, but I think there are myriad other vendors selling the same thing. I chose Bluetooth because the iPhone seems to have problems with some WiFi versions. I think Android works with both pretty well.
I did do the lifetime upgrade to the Pro version of the app, for like $6, because it allows me to display more simultaneous parameters, but the free version works fine as well, just limited to like 2 variables at the same time.
Edit, here is what I bought. It went up $5 since I bought mine (like everything else in the world).
https://www.amazon.com/Viecar-Bluetooth-Android-Diagnostic-Multi-Brands/dp/B01MTKSCEJ/ref=sr_1_5?crid=1TZZGXZQ5DZDM&dchild=1&keywords=viecar+bluetooth+4.0+elm327&qid=1621533523&sprefix=Viecar,aps,222&sr=8-5
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swathdiver
Full Access Member
Haven't been able to pull up Alcohol Content with the Torque Pro app but can see it with the Dash Command app.
Mine is staying at 73% today. Almost time to refuel, next time out probably.
I assume you are using E85. Have you used the water bottle test to see how your virtual sensor is doing versus the actual content of your E85?
Thanks. I have the OBDLink MX+ Bluetooth dongle, just need to figure out a good Android app for the small tablet I use.
swathdiver
Full Access Member
I have in the past but not lately. I'll see about pulling another sample soon.
Holy smokes, so your truck thinks it has 73% Ethanol and you are pumping E10?
swathdiver
Full Access Member
No, no, when I wrote that earlier today it was finishing up its 3rd tank of E85 and the Tech-2 read the alcohol content at 73%. A couple of days before it mirrored the last tank, 62%. It was 28 days since my last refueling. Spent an hour looking for my fuel rail adapter and no joy. It's around here somewhere!
Thanks Ken, it's Greek to me but will see if my kids can figure it out.
Got it. 73% sounds quite plausible as an accurate number for E85. It would be really interesting to know how close it is to what is actually in your tank.
I may try E85 next and do my bottle test with the stream I am putting in my tank to see if my virtual sensor is any better at calculating E85 percentages, cause it definitely isn’t very good with Zero or E10.
Getting E85 is a little bit of a pain here as the one pump within reasonable driving distance charges about what my best price on 87 E10 is here, so effectively more expensive than E10 premium on a cost per mile.
kbuskill
***CAUTION*** I do my own stunts!
You can create a custom PID... just enter the information that I posted in those screen shots.
Your girls are smart... they can figure it out.
swathdiver
Full Access Member
It usually takes 3 to 5 tanks to get up to full strength E85. Highest I've seen is 80% at these Sunoco pumps. I refueled on the way home from dinner tonight, about 5 miles from the house. Once I find that adapter, I'll make sure the truck has run at least 40-50 miles before taking a reading with the Tech-2 or Foseal OBDII and Torque Pro.
most likely you have an issue with the ethanol sensor. or fuel sensor it's actually a real sensor..OK, final update for this fill. The E% calc after the first cold start after a fill (I had two warm starts after the fill), the % is the same as the final calc after the second warm start, 19.38%. About 19% above what is actually in the tank.
I changed the canister purge valve to a new OEM unit and also installed a new OE E85 gas cap and did get a monitor complete on the Evap, so it looks like the canister purge valve isn’t playing a role in the poor performance of the virtual ethanol sensor.
I am thinking I am not going to get to the bottom of this issue. Glad I got the Tech 2 to reset it to 3% when it gets up into the 30’s percentage range.
Ask the person working at the Gas station what Percentage the E85 is they will have the sale sheet they get from the fuel truck guy...
also the sensor can be dirty so run some fuel injector cleaner
(note this is just an example not the actual one for your suv)
Amazon.com: 12568450 12570260 Flex Fuel Sensor Replacement for 2000-2003 Chevy S10, 2002-2005 Chevy Silverado 1500, 2002-2005 GMC Sierra 1500, 2002-2005 GMC Yukon 2.2L 5.3L: Automotive
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Very hard to clean or replace a virtual sensor.
kbuskill
***CAUTION*** I do my own stunts!
GM, in all of their infinite wisdom, did away with the physical flex fuel sensor on the GMT900 platform, it is probably sitting in a box on a shelf, along with the cabin air filter, lights under the dash and on the door panels, at GM headquarters.
The GMT800s have an actual FF sensor but the GMT900s use an algorithm, based off of different parameters including the O2 sensors, to deduce the ethanol percentage.... or perhaps a crystal ball.... lol
gooffeyguy
Tom
A lot of interesting info in this thread. I always thought there was a sensor, but then why would it fluctuate so much after a refuel if there were. Makes sense now.
I refueled with E85 yesterday. Price finally went up a bit, from $2.09 to $2.29. This was my 3rd refuel of E85 since coming back from spring break where I last had E10.
My % before fillup was 72.55. After fillup it fluctuated down to 58, then up, then down, and finally settled to 71.76. I also checked it this morning to see if it did the change after the first cold start, but it was the same, 71.76 %
Sent from my SM-G930V using Tapatalk
I refueled with E85 yesterday. Price finally went up a bit, from $2.09 to $2.29. This was my 3rd refuel of E85 since coming back from spring break where I last had E10.
My % before fillup was 72.55. After fillup it fluctuated down to 58, then up, then down, and finally settled to 71.76. I also checked it this morning to see if it did the change after the first cold start, but it was the same, 71.76 %
Sent from my SM-G930V using Tapatalk
Thanks for the information. 71.76% sounds pretty plausible as a real value for E85. After I burn down this tank of zero, I will fill with E85 and test it with the bottle. Maybe my virtual sensor will be more accurate on the other end of the scale.
