Leaner mixture during tires slippage after launch

Hi.

It's been noticed the A/F mixture is getting leaner than target afr when tires are slipping after launch whilst it matches the target afr when you get a good grip without tires slippage. Can anyone explain why it happenes?

Maybe it's due to the ECU accessing untuned area of the map. My guess would be higher RPM but lower load. Can you do a ghost trace on the map to see which cells are being accessed while this condition happens?

It is always the same when using speed density regardless the brand of ECU. I have spoken with many guys experiencing the same thing. Same load, same engine rpm but different afr... I have an idea why it is happening but I'd like to hear from other people first...

I'm curious as well, let's see what the others are gonna say!

More than likely prediction built into the fuel model and transients being affected by a different factor of time.

Bingo! That is what i thought...

What are the injector pulse widths doing at this point? Do they reduce in duration to match the lean, or remain the same? If you are using ignition cut to control the engine torque it may be that you are seeing a lean value on the lambda trace due to the fuel not being combusted and thus leaving an excess of air in the exhaust stream.

I assume you're using a timer for the enrichment - as David said, any tyre slip will take the engine's RPM rise out of phase with the enrichment roll off.

It was a big problem with top fuel drag cars because they had to be mechanical, and they used timers for their fuel curves which could get out of phase with tyre shake, miss-set clutches, and/or if the driver had to 'pedal' through wheelspin.

Hi, Stephen.

Yes, that was one of my first thoughts that fuel isn't fully burned causing WB to read lean but I didn't think it is logical enough since I'm not using ignition cut for traction control and injectors pulse width stays the same.

Gord,

acceleration enrichment issue was also one of my thoughts at very beginning.