009's all done @110% Duty Cycle? (T+ tuning)

[bruce]

Originally posted by Razor
but exactly how does one know for sure the injectors are at 100 percent..I know Direct scan does a computation to calculate this with values it recieves from various sensors.but what is the formula for this determination..

If load is at 254 and Maf is pegged at 255 ...what other parameter is involved in the correllation to the injectors being static..

And finally How is an AFR calculated on direct scan..and how accurrate is it?

Time available vs PW, tell you duty cycle. The ecm calculates a PW, DS compares that to time available, and bingo Duty Cycle.
I've hooked a dwell meter in series with an injector, and the reported figures all line up within a few %.

An injector going static is about not having enough time to shut off and turn back on again. If you build an ecm bench and hook an injector up to it, you can plan as day hear it when it stops cycling, and also when it chatters.

DS doesn't calculate the AFR it displays, it just reports what the ecm has stored as a it's COMMANDED AFR. As long as the info into the ecm is accurate then the data out is accurate. Peg the MAF and then the MAF numbers are bogus, and so are the Commanded AFRs. Also, removing screens, changing air filters all will skew the MAF. As designed it's right, as folks modify things then the greater the error.

The ecm uses a part of the processor as a scratch pad, just writting values down for future use, DS accesses those areas and reports the values. The DC, Tor, HP and Accleration are DS functions, and not related to what the ecm is thinking about.

 

[BEATAV8]

Razor,
Here's some more info you may find useful:

You can also think of duty cycle as a percentage of two full crank rotations. Our little 4 stroke V6 fires each cylinder 1 time for every two crank rotations, or 720 degrees. Each injector has to deliver it's fuel for it respective cylinder during that 720 degrees. A 100% duty cycle would represent an injector that is on for that full 720 degrees, as well as the next 720 degrees! 50% DC would mean the injector was on for 360 degrees and has a break for 360 degrees before firing again.

To calculate the number of crank angle degrees the injector is firing:

(360 degrees/rev)*RPM*(1min/60sec)*(.001sec/milisec)*(Injector PW miliseconds)

or shorten it up and keep it simple: .006*RPM*inj pw milisec=# of crank angle degrees

Change that number of crank angle degrees into a percentage of 720 to get injector duty cycle. Percentages great than 100% just mean the injector is on full time.

Like Bruce said, the A/F ratio is a commanded value. The mass air flow number can be converted from grams per second to lbs/hr by calculating the following: (will use 255 grams/sec as an example)

(255 g/sec)*(.002205lb/gram)*(3600sec/hr)=2024.2 lb/hr of air flow

divide 2024.2 lb/hr of air by the commanded A/F ratio: (example A/F ratio=12.6)

(2024.2 lbs air/hr)/(12.6 air/fuel)=160.65 lbs fuel/hr

160.65 lbs fuel is a total, divide that by 6 (the number of injectors) and you get: (160.65lbs/hr)/6=26.7lbs/hr

Shows that for a commanded A/F ratio of 12.6 and a true mass air flow of 255g/sec, the stock 28 lb/hrinjectors should be well matched to the system.