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post #11 of (permalink) Old 11-02-2017, 08:54 PM
racingvette
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Re: Just wondering

3% is too low of effects of E10 over weather and elevation changes

The C6 Z06 427 LS7 runs hotter then LS3s do, this alone induces more engine knock and cost of performance numbers GM would not want

As compared views below GM had to set the C6 Z06 LS7 tune for fuel trims from 5 to 8% richer (to make up the 7% leaner due to E10)
(then what C5 Z06 LS6 AFR was set to) from idle to even only 2,500 RPMs
As the elevation, air and coolant temps go up the PCM is slanted to go even richer

Makes no difference what non Ethanol or high amounts of Ethanol used as this OP is about running too rich at startup and idle - what the causes were
OP had car to dealer for some days and they could not find any problem ( as AFR is GM set to rich)

The fact GM had to slant the fuel trims richer due to E10 where they did not for older Corvettes that the E10 had ill effects to AFR so C6s had to be set richer in GM calibrations

So if the engine at cold start and idle is running -8% rich fuel trims with E10 as GM tunes below shows rather then for years running a 14.2:1 (stoch) AFR GM had to lower that to 13.9:1
That means GM tune is set to on purpose command richer AFR to help reduce the engine knock from E10

Now when the OP has a dirty air cleaner (less airmass) and using non Ethanol gas the fuel trims then will be even richer and that is what the OP found doing OBD-II scans where on cold start
the fuel trims were 15% plus too rich. Will not make a good cold start

So a tuner says, clean air cleaner and run some E10 and using a scanner see what the effects are and what the fuel trims then look like when driving at their higher elevation
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Mike M - 2001 / 2008 Z06s
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