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Adding PI to supplement DI - Lambda fast controls

Understanding AFR

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I am integrating PI to supplement the factory DI system to run E85. As I dial in the blending tables, I am monitoring lambda fast controls and lambda actual. My question is how close to 1.0 do you want to get for fast controls on a WOT pull? Is it better to be slightly below 1.0? The system seems to do a good job of hitting target even when fast controls are 0.7-0.9, and I prefer seeing the system go a little rich vs going a little lean on 40 psi WOT pull, but curious what more experienced tuners shoot for.


I'm not familiar with "fast controls". What are you referring to? Is that a gain on closed loop fuel trimming?

Please let us know what you're trying to achieve as that might also help us better offer advice.

Correct, it is the Audi closed loop fuel trims. 1 is no intervention, above 1 is adding fuel and below 1 is pulling fuel out.

Ok thank you.

+/- 10%, in this case 0.9-1.1 would be a good starting point, with +/-5% being more ideal (0.95-1.05 in this case). I've had cars that could hold +/- 3%, but don't beat yourself up if this car won't stay in that range.

Keep in mind this is under steady state conditions such as idle, gentle driving, and full throttle operation after throttle plate position and intake manifold pressure have stabilized. During rapid throttle motion and/or rapid MAP delta, fuel trims will often briefly exceed reasonable expectations of steady state behavior.

And a little add on...ideally within that range you won't have situations where trimming needs to jump from 1.05 to 0.95 as you move the engine through adjacent engine speed or load areas. For example at MAP of 100 kpa, engine speed 2000, you should have similar fuel trim to 100 kpa and 2400 RPM, but perhaps idle will have trim 0.97 and cruising will be 1.02. You just don't want the engine jumping from areas that are significantly overfueled to areas that are significantly underfueled for example, because trims can only respond so quickly.

I appreciate the feedback! I will target that 0.95-1.05 area. I am road tuning, but running through many scenarios such as different pedal aggression and shifting at different RPMs to see how fueling responds to dial in various cells in my maps.

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