Ethanol percentage flex fuel

[wsteele]

So I had started another thread on my trucks loose gas cap CEL and code and it morphed into a long discussion on Ethanol percentage reporting my the truck and how it seemed to affect the operation of the engine.

Until I started fooling around with a few different scan tools, I was never aware that my truck thought it was running a significant percentage of E85 in each tank.

I noticed that when the scan tools said the PCM thought it had 38% Ethanol, when the engine was warming up, it was a lot smellier than normal, a pretty rich unburned mix was being produced, not carbureted race engine rich, but much richer than normal for this engine.

My assumption was the engine when running in open loop was dumping a lot more gas than needed, thinking it had a lot more Ethanol content in the mix. Once it warmed up a little and the engine went into closed loop the short term trims seemed to get back to normal pretty quickly and things cleaned up. I don't know for certain this is what is happening, just a hypothesis.

A while back, I decided I would run the tank way down, refill with a zero Ethanol gas at a local 76 station and then reset the Ethanol monitor with my Tech 2. After I reset it, it read 3% (which is what I think the Tech 2 sets it at) and that is where it sat for the whole tank of 0% Ethanol 76.

Today, I refilled at my normal 10% or less Ethanol (Costco) and had my scan tool dongle plugged in, with my scan app going on my iPhone. I set the live data to display my O2 sensors (I just changed them and wanted to see if they seemed normal) and also had it display the Ethanol percentage.

Wow, while driving around (many different driving modes, freeway, in town, hill country up and down), I watched that Ethanol percentage hop all over the place. It jumped pretty quickly up above 18% and stayed up there for maybe the first gallon or so. It then dropped down to 8%+ for another long while. Toward the end of the driving (maybe 2-3 gallons total), it was back down and steady at 3.14%. Very strange indeed.

I will keep an eye on it for this tank and report any changes in reported percentages. Right now it is just a curiosity, as I know how to get it back to 3%, but I really want to know what causes the gross miscalculations that seem to creep in, when burning something other than Ethanol free gas.

 

[gooffeyguy]

I know mine will fluctuate for a bit after a fill-up, but only for about 10 miles maybe. I believe the computer is trying to calculate the correct alcohol percentage with the help of the long term fuel trims seen by the O2 sensors.

I did not know the Tech2 could reset the alcohol percentage. What menu is that under?

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[wsteele]

I know mine will fluctuate for a bit after a fill-up, but only for about 10 miles maybe. I believe the computer is trying to calculate the correct alcohol percentage with the help of the long term fuel trims seen by the O2 sensors.

I did not know the Tech2 could reset the alcohol percentage. What menu is that under?

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I will have to go back and run through it to find it. I am still learning the Tech2. Pretty sure it was under one of those special functions line items.

Mine got back to the 3% number it started with before fill-up. But during the ride is was jumping all over the place. If the calcs are based on the long term fuel trims, perhaps my erroneous calculations that seemed to persist will be addressed with my new O2 sensors. They seem to be working well, at least after they warm up.

 

[swathdiver]

Today, I refilled at my normal 10% or less Ethanol...

Wow, while driving around (many different driving modes, freeway, in town, hill country up and down), I watched that Ethanol percentage hop all over the place. It jumped pretty quickly up above 18% and stayed up there for maybe the first gallon or so. It then dropped down to 8%+ for another long while. Toward the end of the driving (maybe 2-3 gallons total), it was back down and steady at 3.14%. Very strange indeed.

Not strange at all. This is how the system calculates the alcohol percentage. What causes it to go awry is when you refuel and then drive a few miles to go home and or making lots of short trips. The computer needs at least seven miles to calculate the alcohol percentage after refueling. Even then, it may re-calculate even days later in an attempt to be as efficient as possible.

 

[wsteele]

One thing on using the Tech 2 to reset Ethanol percentage. I forget where I read it, but it was very clear that resetting it with a lot of Ethanol in the tank can be problematic.

Edit, I think the above warning was on the reset page itself.

 

[wsteele]

OK, here are the screen shorts of the nav to the Ethanol reset procedure on the Tech 2. This may be model/year specific, so YMMV.

 

[bigdog9191999]

i never thought to moniter this in ours, we only have one that is flex, but now i am gonna have to see what i can use to watch ( hoping my dongle with smartphone, and torque is enough) worst case i fire my windows tablet and hook up the old hpt and give it a look.

 

[swathdiver]

One thing on using the Tech 2 to reset Ethanol percentage. I forget where I read it, but it was very clear that resetting it with a lot of Ethanol in the tank can be problematic.

Edit, I think the above warning was on the reset page itself.

Correct, only reset with E10 in the tank.

 

[wsteele]

So after today’s driving, maybe 25 miles, it settled in at 17% Ethanol. It seems to really struggle with any Ethanol, versus the Ethanol free (which it stayed rock solid at the 3% reset number).

The current mix is less than 10% (80% < 10%, added to 20% 0% Ethanol, which should yield <8% total Ethanol). Right now my Yukon thinks I have double that amount.

I will continue to report results as I burn this tank down.

 

[wsteele]

Correct, only reset with E10 in the tank.

It is surprising you can’t set the target amount to a specific known number, versus just resetting to a fixed 3% number.

 

[swathdiver]

It is surprising you can’t set the target amount to a specific known number, versus just resetting to a fixed 3% number.

Well, as soon as the system detects a refueling event it's going to begin recalculating anyway so maybe that's why they didn't allow for that.

 

[wsteele]

Well, as soon as the system detects a refueling event it's going to begin recalculating anyway so maybe that's why they didn't allow for that.

It just seems like you would want to be able to set it to where you know it is, versus having to know you have less than 10% in the tank before performing a reset. I guess the only real glitch is when you reset it and have E85 in the tank, with the risk of it not running at all to be able to get it to closed loop and start correcting on the fly.

 

[iamdub]

Are you going by the advertised Ethanol percentage? This can vary wildly, especially at an "E85" pump. The only way to know your actual alcohol content is to measure it. I have this to measure it: https://www.amazon.com/Etched-Ethanol-Content-Tester-Gasoline/dp/B07NMV8WGP

As James mentioned, it takes at least seven miles of driving (mainly cruising) for the system to "accurately" calculate the content. Hard throttle (in PE) or stopping with engine off can really throw off its calculations.

 

[gooffeyguy]

E85 isn't always (and hardly ever) 85%. It can range from like 55-83%, or something like that.

Regular (E10) isn't always 10% either. On the pump it says it may contain up to 10%.

I got gas today. Second time since I've been back from the trip to NOLA, in which I ran a few tanks of ExxonMobil 93. Last time I fueled up was with e85 and my % before filling today was 55.

After filling up with 24 gallons of E85 (@$2.09), I watched the % on the Torque app on my phone. It dropped to 40 for a few minutes, then up to 60 for a minute, then to 55, then up to 66, and I think it finally settled at 69%. There might have been a couple #s it jumped to but I didn't catch due to having to drive.... lol.

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[wsteele]

Are you going by the advertised Ethanol percentage? This can vary wildly, especially at an "E85" pump. The only way to know your actual alcohol content is to measure it. I have this to measure it: https://www.amazon.com/Etched-Ethanol-Content-Tester-Gasoline/dp/B07NMV8WGP

As James mentioned, it takes at least seven miles of driving (mainly cruising) for the system to "accurately" calculate the content. Hard throttle (in PE) or stopping with engine off can really throw off its calculations.

The gas I have been using for quite a while (not counting the 0% Ethanol I used for the reset test) is Costco (advertised as less than 10% Ethanol). My Yukon has @calculated” high 30’s% Ethanol for quite a while with this gas.

When I did the test with the 0% and the reset with the Tech2, it stayed at the 3% reset number for the whole tank.

For whatever reason, a little Ethanol content really seems to fool with the calculation.

My assumption is something sensor wise is causing my truck to misread how much Ethanol is in the gas.

 

[iamdub]

My assumption is something sensor wise is causing my truck to misread how much Ethanol is in the gas.

Such as the lack of a sensor. lol

 

[wsteele]

Such as the lack of a sensor. lol

Right, so what it is using to calculate it must be sending bad data. Or Costco is putting 30+% Ethanol in their <10% Ethanol gas (pretty unlikely).

 

[wsteele]

Such as the lack of a sensor. lol

My assumption was my PCM was calculating an incorrect Ethanol content due to really tired (original) O2 sensors. I changed out all 4 and the exact same results occur. The Ethanol content calculation just seems to get higher and higher, tank to tank of the Costco <10% Ethanol (with some Shell and Chevron <10% Ethanol thrown in).

When I found the reset function on the Tech 2 I was excited as I could see if running 0% Ethanol would still yield an ever creeping higher Ethanol calculation (and seemingly ever richer open loop mixture). In fact, when I pumped a tank full of the 0% and reset it, it stayed right at 3.14% calculated content through the whole tank (the number the Tech 2 reset it to).

As soon as I started using the Costco gas again, it started moving up. I have used about a quarter of a tank of the latest fill of Costco Regular and it finished at 17% today. I suspect before I get to refill time it will be over 30% calculated.

I wish I knew what that algorithm looked like, what sensor input it relied on, to calculate the %. Then I would at least know what I might try to change out, clean, etc.

 

[Fless]

This situation cries out for an ethanol percentage test at the pump (@iamdub posted a tester), midway during the fill-up. That minimizes errors from fuel left in the hose from the last person who fueled up, with possibly different fuel.

Then a similar test perhaps halfway through the tank, taken from the fuel rail. That would verify what's going in and what's really in the tank.

IIRC the ethanol is added separately to the station's tanks by the tanker driver, and that could cause varying percentages. Hard to know what's going on without testing.

 

[wsteele]

This situation cries out for an ethanol percentage test at the pump (@iamdub posted a tester), midway during the fill-up. That minimizes errors from fuel left in the hose from the last person who fueled up, with possibly different fuel.

Then a similar test perhaps halfway through the tank, taken from the fuel rail. That would verify what's going in and what's really in the tank.

IIRC the ethanol is added separately to the station's tanks by the tanker driver, and that could cause varying percentages. Hard to know what's going on without testing.

Perhaps you guys are right. It just seems kind of far fetched that I would be getting 30+% Ethanol in gas that each pump advertises boldly (less than 10% Ethanol), but I guess it would be a profit adder to the distributor if they decided to just keep adding Ethanol to the tank. It is easy enough to test. I will post the results.