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My AFR gauge showing 17.6 at idle

EFI Tuning Fundamentals

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If my AFR gauge is showing 17.6 at idle (when engine is warm) and I know that I'm aiming for 14.7

Is the right calculation: 17.6 divided by 14.7 = 1.19 meaning I need to add 19% of fuel delivery?



That could be correct. But be sure that you aren't getting a false lean reading at low flow volumes. One trick I try is to place my hand over the exhaust exit so that fresh air isn't drawn into the exhaust (not completely sealed, just not completely open). If you do this and the AFR gauge changes richer, you know that it's been reading some of the outside air, and the readings with the exhaust covered are closer to the actual mixture.

Depending on sensor placement you can get dilution from the backnof the exhaust or from intake/exhaust overlap if the engine has aggressive cams/ports which means you read leaner than the actual in cylinder combustion.

Thanks for the tip!

Will do!

As Slides said - they are quite expensive, but a 4/5 gas analyser will allow you to check for hydrocarbons (unburned fuel that would have reacted with the oxygen in the air) and carbon monoxide, which would be partially burned fuel. They, with the loxygen levels, would help optimise fuelling for cruise, especially with a lot of overlap.

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