Alcohol Percentages

[409Jake]

Quick question for you all... Not really an issue, but more so from curiosity side of things...

Have a 2012 Avalanche (5.3) that I started scanning tonight to see where the factory tune stands. Trims are off around 5% or so, so they're not too far out of line, only mods are a k&n cold air box.

The curious thing for me was that I happened to log afr and noticed the commanded afr was 12.82 throughout a 20 minute log, so I added the alcohol sensor (Alcohol % SAE) into the pid list just to see what it said too. I was surprised to see that it displayed 33%, since I've never had anything other than 87 - 93 octane, never e85 fuel, for 7K miles on it...

I would have expected to see maybe E10 percentages, but was surprised that it was at 33%. I pretty much use the same gas station all the time, so I'll have to change it up on the next tank and see what happens.

Anyone else ever see values like that in the alcohol percentage on regular gas?

[eficalibrator]

Does this vehicle have a physical sensor on the fuel line or does it use the "virtual sensor" strategy? If it's the latter, it is quite possible that errors from the cold air kit are affecting the ethanol percentage calculation.

[409Jake]

I believe its the virtual deal since this is a 2012 truck...

In regards to the errors, are you referring to the trims, or is there another set of errors behind the scenes? Trims aren't real ugly, mostly 5%. Its still running the factory cal so far and I haven't started any cleanup anywhere yet..

[eficalibrator]

Part of the virtual ethanol sensing uses fuel trims after a refueling event and attributes part of this to an inferred ethanol percentage. So if your cold air kit skews the fuel trims by 15%, you will see a significant change in inferred ethanol percentage accompanied by some smaller residual fuel trim. Keep in mind that a 15% alcohol percentage is NOT equal to a 15% fuel trim!

Fixing this correctly basically requires that you test the fuel, clear the trims and alcohol learns and re-map the MAF curve to match your new airbox. Once you do this, you should see more realistic alcohol percentages and fuel trims.

[Area47]

Quick question for you all... Not really an issue, but more so from curiosity side of things...

Have a 2012 Avalanche (5.3) that I started scanning tonight to see where the factory tune stands. Trims are off around 5% or so, so they're not too far out of line, only mods are a k&n cold air box.

The curious thing for me was that I happened to log afr and noticed the commanded afr was 12.82 throughout a 20 minute log, so I added the alcohol sensor (Alcohol % SAE) into the pid list just to see what it said too. I was surprised to see that it displayed 33%, since I've never had anything other than 87 - 93 octane, never e85 fuel, for 7K miles on it...

I would have expected to see maybe E10 percentages, but was surprised that it was at 33%. I pretty much use the same gas station all the time, so I'll have to change it up on the next tank and see what happens.

Anyone else ever see values like that in the alcohol percentage on regular gas?

your cai skewed the final reading number. dealt with this in the past on various trucks. put on the stock air box. load a stock maf curve back in the file, go fill up and watch what the fuel trims do. more or less what efi stated. the closer you can get to zero % ethanol the better for getting the maf scaling back in line. once the maf scaling is set with in the range you want for part throttle and wot scaling, leave it be.

[409Jake]

Thanks for the responses! Good info to know here. Didn't realize that just a cold air box would have thrown off the alcohol percentage calculations, especially with just a 5% error in the factory trims.

Since the truck has not been tuned yet, I'll throw the factory air box back on, reset the trims, and run a fresh tank through it to see if the alcohol percentages come back in line as a test.

Thanks again!