Injector slope AFR tuning
Now that my Sport is quite drivable using MTF AFR tuning I've decided to make another attempt using injector slope AFR tuning. Here are some injector specifics from the calibration summary:
AHISL (high injector slope) = .016741 lb/sec or 60.27 lb/hr
ALOSL (low injector slope) = .017552 lb/sec or 63.19 lb/hr
FUEL_BKPT (fuel mass to switch between high and low slopes) = .00003363 lb/pulse
On my earlier attempt I used the above and an MTF from bench airflow testing of a Lightning 90 mm MAF sensor. The AFR varied from rich to extremely rich as load increased.
Below is a graph of my Siemans Deka 60 lb/hr injectors.
Using the graph I derived the numbers for comparison to the published data.
AHISL = 43 mg/6 ms or 7.167 g/s or .0158 lb/sec or 56.9 lb/hr
ALOSL = 10 mg/1 ms or 10 g/s or .02204 lb/sec or 79.34 lb/hr
FUEL_BKPT occurs at a pulswidth = 1.7 ms x .0158 lb/sec = .00002686 lbs/pulse
Since my derived parameters were fairly close to those published I concluded the published data was accurate. Next, I created three tunes and data logged each during short drives. I limited the throttle (load) to keep the AFR on the wideband meters above 10:1 since that is their lower limit. Then I plotted actual lambda vs MAF AD counts. The commanded lambda was .99 for each plot.
Plot A: AHISL=.0234441 lb/s, ALOSL=.0246 lb/s, FUEL_BKPT=.0000471
AHISL is 2.54 times the published and others scaled accordingly.
Plot B: AHISL=.02981 lb/s, ALOSL=.03121 lb/s, FUEL_BKPT=.0000625
ALOSL is the max allowed by Advantage 3 and others scaled accordingly.
Plot C: The only difference between B & C is The Returnless Fuel Pump, Fuel Rail Pressure was changed from 39.15 to 100 psi in the tune.
It is obvious from the plots that the 60 lb/hr injectors are way bigger than what I need for my modest power increase from 160 rwhp NA to 227 rwhp FI. I should have selected Deka 40s which would have allowed me to double my horsepower. I was surprised that changing the Fuel Rail Pressure in the tune made a difference since Injector Comp for Pressure was disabled.
My next attempt will be to double the fuel injector slopes and breakpoint multipliers from 1 to 2 and restore the Fuel Rail Pressure in the tune to the actual of 39.15. This may not have any effect since my stock strategy is set up for a returnless fuel system with no fuel pressure sensor.