26 Jul 2016

When engine “v1.0” was tuned, one of the many ECU settings was a mode called “deceleration fuel-cut.” It made sense to have, cutting fuel when coasting, so it was enabled and not given any more thought. I recently read that a side effect of fuel-cut is that it makes engine braking much more pronounced and wondered, especially after watching the car jerking back and forth in the Streets of Willow skidpad video, whether fuel-cut could have been the cause. I also wondered if it could have contributed to the Turn 9 spin at Willow Springs, where letting off the gas caused enough engine braking that it helped initiate a spin (that’s it, not a lack of driver talent!).

Just for fun I tried disabling it – and it was a night and day difference! Throttle control is much smoother and much more controllable. I asked a buddy about this, who reached through the Interweb and “dope-slapped” me, saying there’s a lot more than just enabling it, that it’s only supposed to be enabled when:

Throttle position is <2%

When the condition persists for more than 0.5 seconds

When MAP is just below idle MAP

That said, after it was disabled I’ve yet to see a downside. The car runs fine and doesn’t flood or stumble, and the spitting, popping and crackling under throttle-lift makes me smile, so for now it stays 🙂