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I've been tuning the fuelling for my B20 using a Hondata S300. What should the ARF be on the overrun? I'm assuming it should still be getting some fuel? However my fuel appears to be getting cut completely a few seconds after coming off the throttle and will stay like that until you open the throttle again. Surely this is not correct?
Normally you would want to use an over run fuel cutoff strategy to completely disable fuel injection. This is done for fuel consumption and emissions purposes. Just about every ECU I've tuned has this option and allows the over run fuel cutoff to be enabled above a certain rpm and below a certain throttle setting. If you are using this feature, the AFR reading will be very lean as fresh air will be passing through the cylinder and read by the oxygen sensor.
Ok, so its fine for no fuel to be I injected on the overrun? I was worried it may damage the engine as it didn't do this on my old ECU so I really noticed it when my AFR gauge started displaying AIR on overrun.
As long as its normal and my engine is safe all is good.
Yes absolutely. Over run fuel cut is employed on OE ECUs for emissions and economy purposes. There is no reliability downsides to this.