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Steve the tuner emailed me and asked if I would attach your last scanner recording values since you did not know to do it
Even though you mixed some E10 with the non Ethanol fuel and first drive the OBD-II scanner shows the fuel trims have already coming down and close what would
be seen with E10,
Once you get through that tank and then full tank of E10 the fuel trim values should be even better.
Values seen on this drive are about what was expected where before fuel trims were -17-20 plus percent rich and now about -8% rich and that is in 56 degree weather
You could look next year summer heat what fuel trims look like and decide which fuel is good at the 2500-3000 feet elevation but since you only do street speeds
it may not be worth the high cost of non Ethanol gas at that elevation since the GM tune is slanted for E10

Later on when not worrying about GM warranty you could consider having a custom tune done to allow for the better non Ethanol gas and the performance gains of that fuel
and tune gains

Nice to see the cold start issue now gone

Suggestions were :

Put that other half of Seafoam into intake manifold while at idle, if cannot do that put in engine oil
Since the engine has been running way rich for months is take sparkplugs out, clean and re-gap them
Take front O2 sensors out and use a propane torch to heat up ONLY tips of them to burn off any carbon buildup
To limit blowby and engine reverb is next time changing engine oil to go with a bit on oil viscosity

Use lower gears to use higher RPMs ( rather then high speeds) and loads to help blow out carbon and allow PCM to learn/adjust fuel trims for all engine loads
and allow the carbon breakup from the Seaform to exhaust out.
If the vehicle is seeing -17 to -20 ltft then its either been tuned already or something mechanically is wrong. A stock GM tune will not be this far off regardless of E10 or E0 being used. A stock tune with a properly installed CAI should also not be causing drastic negative ltft either. A CAI assuming it actually works and didn't make air flow worse should flip the ltft to the positive side if anything. The simplest thing to do is validate the CAI is installed correctly or re-install the stock air filter. There are ways to identify if the vehicle has been tuned. If its a manual and the cags isn't being enforced and there is no local bypass hooked to transmission then its been tuned. Another easy way is to state at what temp the fan turns on while the car is stationary. Anyone here can validate if that fan temp is stock or not. Another way is to have someone with hptuners or similar pull the tune and compare to stock file. A car with that far negative ltft has either been tuned already or has a mechanical issue. There are many corvettes out there being driven by owners that don't know their vehicle has been tuned.
 

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Discussion Starter #22
racingvette, Steve here, It seems my starting trouble ( rough idle ) is gone and I don't know what fixed it. Also since using E10 gas it seems the fuel trims are down to normal. Here in Va. the temp also came way down anyway I thank you and Tuner for all the help.
Steve
 

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racingvette, Steve here, It seems my starting trouble ( rough idle ) is gone and I don't know what fixed it. Also since using E10 gas it seems the fuel trims are down to normal. Here in Va. the temp also came way down anyway I thank you and Tuner for all the help.
Steve
Steve it has been a few weeks since you did the cleanup and using E10 as suggested and being you also say once using E10 the fuel trims leaned out
I think you did the right thing and problem is gone

Stay with the E10, cold weather, you do not race, street driving, you do not need to spend the extra money for non Ethanol gas as GM tune is not slanted for that
Once weather gets hot check the fuel trims and decide if then it is worth non Ethanol fuel or have the PCM tuned for that gas if that is what you want to use.

Good job you did much better then the dealer having the car for multi days and not finding the problem but if they did as you did and saw the -17-20 % rich fuel trims
they would then zoom into that.
Keep using your OBD-II scanner, you will learn more and have the experience in using it.

Have fun with with your C6 Z06
 

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That recommendation was probably made because E10 will lean the car out a bit. Stoichiometric AFR for E0 is about 14.7:1 and stoichiometric AFR for E10 is around 14.1.

Therefore your ratio is 14.1/14.7 so you would lean the mixture out across the board by about 4%.

Be careful though because if your running rich everywhere besides wide open throttle then you could run a hair lean at WOT after making the change. The car needs to be tuned correctly.
 

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Don't ever use less than 93 octane for Z06s it will harm the gas pump and many other issues in timing "retard or knock".
Here in Lebanon we use 95-98 octane gas for all cars. But for me I always put in my corvette 98 octane.
 
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