Virtual or Reality?

[swathdiver]

Was recently asked to do a comparison between what the engine computer shows as the alcohol content and by taking an actual sample of the onboard fuel from the fuel rail.

Both vehicles have been driven less than 30 miles since refueling.

The 2012 6.2 Sierra showed a virtual alcohol content of 21% and the actual measurement came out to about 19% after letting it sit for 10 minutes or so. This truck was refueled two days ago.

The 2009 5.3 Yukon XL showed a virtual content of 77% and the actual measurement came out to about 80% after letting it sit for less than 5 minutes. This truck was refueled today and the fuel has about two hours of run-time on it and the beaker was slightly over-filled.

 

[wsteele]

Was recently asked to do a comparison between what the engine computer shows as the alcohol content and by taking an actual sample of the onboard fuel from the fuel rail.

Both vehicles have been driven less than 30 miles since refueling.

The 2012 6.2 Sierra showed a virtual alcohol content of 21% and the actual measurement came out to about 19% after letting it sit for 10 minutes or so. This truck was refueled two days ago.

The 2009 5.3 Yukon XL showed a virtual content of 77% and the actual measurement came out to about 80% after letting it sit for less than 5 minutes. This truck was refueled today and the fuel has about two hours of run-time on it and the beaker was slightly over-filled.

Very accurate.

I have been doing a lot of reading on the subject and mine can get way off, as you know.

Lately, a "normal" calculated reading for me is around 19% Ethanol for fuel that has 6% Ethanol in it.

That error does seem to affect cold start open loop mixtures mildly (can smell it a little more than normal), but not terrible. In the past, I have seen as much as 38% calculated for fuel with less than 10% Ethanol (that error produces cold start mixtures that would make a mechanic on a carbed race tune engine proud).

In reading the 2007 MY shop manual. With everything else being nominal (my truck runs great), if the calculated Ethanol is within 15% of the actual tested content, GM says it is good. So officially, at 19% calculated on gas that is 6% actual, my truck is fine.

Now, if the difference is 32%, like it has been in the past at times, that is not considered within spec and entails a few more tests, all of which I have done and in the end entails dropping the tank and doing a complete clean of the tank and fuel system.

Given I am within the 15% error spec right now and only need to reset the incorrect error with my Tech 2 each time I fuel up, as soon as I get one more confirming test completed (testing the fuel pressure with a new gauge I have coming), I am going to do what a good GM tech would do and say "no trouble found" and start thinking about something else, a beaten man.

 

[swathdiver]

Very accurate.

I have been doing a lot of reading on the subject and mine can get way off, as you know.

Lately, a "normal" calculated reading for me is around 19% Ethanol for fuel that has 6% Ethanol in it.

That error does seem to affect cold start open loop mixtures mildly (can smell it a little more than normal), but not terrible. In the past, I have seen as much as 38% calculated for fuel with less than 10% Ethanol (that error produces cold start mixtures that would make a mechanic on a carbed race tune engine proud).

In reading the 2007 MY shop manual. With everything else bing nominal (my truck runs great), if the calculated Ethanol is within 15% of the actual tested content, GM says it is good. So officially, at 19% calculated on gas that is 6% actual, my truck is fine.

Now, if the difference is 32%, like it has been in the past at times, that is not considered within spec and entails a few more tests, all of which I have done and in the end entails dropping the tank and doing a complete clean of the tank and fuel system.

Given I am within the 15% error spec right now and only need to reset the incorrect error with my Tech 2 each time I fuel up, as soon as I get one more confirming test completed (testing the fuel pressure with a new gauge I have coming), I am going to do what a good GM tech would do and say "no trouble found" and start thinking about something else, a beaten man.

Are you testing the fuel in one of those little beakers?

 

[wsteele]

Are you testing the fuel in one of those little beakers?

Yes, that exact one I bought under your suggestion.

It's all over on the Ethanol Flex Fuel thread.