AFR in between gears / throttle close (boosted 6MT)

[patroklai]

Hello, I recently went s/c on the M along with a P3 gauge.

One thing that stood out to me was the AFR reading in between gears. When letting off the throttle, AFrs will jump to 20+, generally 23 but I've seen P3 recall up to 28. From what I've read, aFR in between gears isn't as important as the o2 sensor reading is changed due to the injectors shutting off when off throttle.

However, I wanted to get input from those who have been watching their AFR more closely and ideally do so in similar conditions (boosted / 6-speed manual).

Thanks!

[amrazM]

afrs run full lean when the revs drop, essentially what creates the engine braking decel effect.

[patroklai]

Okay, thanks. From what I've read seems pretty normal, specially on 6MT but was looking to confirm. Thanks.

[BPMSport]

Totally normal, fuel injection is going to be momentarily suppressed as the revs drop, the AFR seen is just a result of the mixture that's still in there. For example, rev the car up to 5k while in neural and watch the RPMs fall, you'll see it go to a full lean condition as it falls down toward idle speed as the engine has time to discharge the fuel mixture completely. It actually even goes lean on a DCT shift as well but it's so much faster that it's nearly unnoticeable on logs unless the sample rate is hundreds of times per second.

Throttle closure based on pedal position is normal, and the M3 has both injection and ignition cuts as well to prevent RPM from climbing in excess of redline.

Hope this helps!

[patroklai]

Originally Posted by BPMSport

Totally normal, fuel injection is going to be momentarily suppressed as the revs drop, the AFR seen is just a result of the mixture that's still in there. For example, rev the car up to 5k while in neural and watch the RPMs fall, you'll see it go to a full lean condition as it falls down toward idle speed as the engine has time to discharge the fuel mixture completely. It actually even goes lean on a DCT shift as well but it's so much faster that it's nearly unnoticeable on logs unless the sample rate is hundreds of times per second.

Throttle closure based on pedal position is normal, and the M3 has both injection and ignition cuts as well to prevent RPM from climbing in excess of redline.

Hope this helps!

That helps tremendously. Thanks Mike.