Stoich value not reading consistently

[CRSilverado]

I've been logging a 13.87 stoich in my 2013 6.2 Silverado but in my 08 Corvette 14.68. I'm using 93 octane in both. What is going on?

 

I did fill up at different stations so maybe I've gotten a different Ethanol mixture???

[oldscsc]

Definitely a possibility. Straight gasoline's stoichiometric A/F ratio is 14.7:1, but E85's is about 9.8:1. I know you're not running E85, but my point is that if you got an alcohol blended fuel, your A/F ratio will be lower than straight gasoline.

[CRSilverado]

Definitely a possibility. Straight gasoline's stoichiometric A/F ratio is 14.7:1, but E85's is about 9.8:1. I know you're not running E85, but my point is that if you got an alcohol blended fuel, your A/F ratio will be lower than straight gasoline.

 

The fuel in my tank now is from an Exon station that was put in by the dealer. I think maybe I need to run this fuel out and see what happens with fuel from the station I normally use (Chevron) in my Corvette and see if this gets me to the same stoich. My Chevron station does indicate up to 10% Ethnol but I still log a 14.68.

[oldscsc]

Regardless, I wouldn't worry about it too much. The truck knows what's going on. Unless it throws a code or you see a driveability issue crop up, just keep on truckin'.

[CRSilverado]

Regardless, I wouldn't worry about it too much. The truck knows what's going on. Unless it throws a code or you see a driveability issue crop up, just keep on truckin'.

 

Thanks, no driveability issues. Truck runs good. No codes. I'll keep on truckin!

[CRSilverado]

Still trucking good but after multiple fill ups I now read 14.4 stoich. Corvette still reads 14.68 with both fueled at the same station on the 93 octane pump.

[music]

When you say you're reading "xx stoich", do you mean as-measured using a wide band, or is that "commanded afr" from the ECM?

[CRSilverado]

When you say you're reading "xx stoich", do you mean as-measured using a wide band, or is that "commanded afr" from the ECM?

I'm reading commanded stoich with my HP Tuner. Do not have a wideband connected to the truck. Just don't understand why even commanded stoich should be different with both vehicles having the same fuel from the same station. The Corvette has always read 14.68 for the last 5 years of logging. Had a wideband on it but don't remember what actual was at the time. In my files for each both have commanded almost the same. Only slight differences.

[music]

Is this a completely stock setup (no custom tuning)?

[CRSilverado]

Is this a completely stock setup (no custom tuning)?

I have an Airaid pipe with the factory filter but all else is stock including the tune. But even with the factory pipe it read differently than my vette.

[music]

I don't know HPTuners, as I've only used EFILive, and only on my 5.3. The commanded AFR vs Ethanol% will be correct from the factory. I suspect that the "Ethanol% estimator" is working correctly, and that you're running 10 to 15% Ethanol. My 5.3 isn't flex fuel, so it doesn't have an Ethanol sensor, afaik. I'm not really sure how it estimates small amounts of alcohol, but I assume that it just watches O2 voltage vs expected, and maybe chamber pressures. I don't think the non-flex method is very accurate, though, as it seems to always reads 14.7, even when there may be ~10% alcohol in there.

 

Edit: I've only been using EFI for about a year, and not very often... so take my input as an "educated guess".

[CRSilverado]

I think maybe you have the answer. My 6.2 truck is a flex fuel vehicle and my 08 Corvette is not. The truck must be getting a reading on the fuel some how like you say. The pump I fuel from says up to 10% Ethanol.