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Understanding AFR: Start-up and Dead Zones

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Start-up and Dead Zones


00:00 Next we are going to deal with the zones labelled dead and startup.
00:04 The start up area as its name implies is the area of the fuel map the engine will be accessing during cranking and initial startup.
00:12 On the face of it this sounds like a really important area since it influences how the engine will start but the reality is that during this period of time, the ECU will be using cranking enrichment and post start enrichment which influence the startup quality much more than the actual target AFR or the fuel table numbers in this area.
00:34 Likewise the dead zones consist of areas in the fuel table we can’t get to during normal engine operation.
00:41 For example we can’t access high boost pressure at 500 RPM, and typically we also won’t operate the engine at 8000 RPM and high vacuum.
00:51 This means we don’t need to worry about the specific tuning in these areas too much.
00:56 For the sake of smoothness and completeness I follow the AFR target trend I have in the rest of the table through these zones, and in the main fuel table I like to achieve a smooth shape to my map in these areas too.
01:10 Most engines exhibit a reasonably smooth and consistent change in volumetric efficiency as load and RPM changes.
01:19 This means that our fuel table should also be smooth and consistent.