Timing vs Duty cycle

[Philv6]

I was out doing some street tuning with alky and I would swear that when I pulled about 4 degrees of timing out my injector duty cycle also dropped from @ 92 to 86 %. What I don't understand is why would duty cycle be affected by the timing? This does not make sense to me.

 

[Lance]

There are not directly related in control.. However, if you decrease the engine's efficiency by retarding the timing (loss of power) and are running closed loop, it's not inconceivable that the duty cycle could be reduced to achieve the programmed air fuel ratio.

 

[pe_turbo]

If you retard timing, the burn won't be as complete so it appears richer at the O2 sensor. If you have O2 feedback enabled, it will try to hit the target you have in the table therefore pulling a small amount out of the mix.