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Old 05-25-2020, 12:44 AM   #34 (permalink)
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Join Date: Jul 2009
Location: New York
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no nickname , it's just a car - '04 volkswagen golf tdi
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EGR is good , more is better , to a point , FREDs fuel is bad

This thread is about driving for mpg which means long periods of low load. This is the type of condition that caused carbon buildup for me in the past. After the tune, which defeats EGR after warmup, my Italian tuneups to blow out carbon are needed much less frequently and show much less carbon when I do. .....

EGR does improve fuel economy by displacing combustion chamber volume with an INert gas (exhaust gas with no or very little 02) that does not support combustion
so EGR makes the engine smaller at cruise AND reduces NOX by reducing combustion pressure wich in turn reduces combustion temperature so it is not as easy for N to combine with 02 to form NOX as that takes place mostly above 2500f .

less combustion chamber volume = less fuel consumed as fuel rate is determined by MAF flow on the mk4 system (primarily) . and MAF can not measure EGR flow so only counts the fresh air charge coming in .

poor quality fuel does not completely combust so it leaves carbon deposits
which decrease flow in the intake add turbulence to flow and INcrease compression ratio & screw up the swirl in the combustion chamber
are an improvement in Fuel Economy

EGR is good
carbon deposits from FREDs fuel is bad

Last edited by mwebb; 05-25-2020 at 12:47 AM.. Reason: is in wrong place
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