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going lean when off throttle

Practical Standalone Tuning

Relevant Module: Road Tuning - Tuning Without a Dyno > Full Power Tuning

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Is it okay that my afr goes super lean when lift the throttle? Afr is around 14 when im doing a pull. Using ecumaster black on bmw m52tu engine

Since you're not spraying any fuel, but still sucking in air it should be at the lowest value your sensor can read. No combustion is taking place on decel.

14:1 AFR is a bit on the lean side for a power run - the engine will tell you what it wants, but I'd expect closer to 13 would be a little better.

If you're using fuel shut-off on over-run it'll certainly be lean, but even without that, the engine has a large pressure differential across the butterflies on over-run and can have more air than might otherwise be expected.


What AFR are you seeing when you lift throttle? Is it the max possible reading, which indicates no combustion as those posting above me have stated?

If by lean you mean it's reading say 15.5 and the sensor value can achieve 18, then the suggestion would change.

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