Injector Duty Cycle question

[LS1Nova]

So what parameter does efilive use to calculate the injector duty cycle? If my ifr table was set lower than it should be would that give me a false injector duty cycle reading?

Thanks,
Frank

[5.7ute]

Injector duty cycle is calculated from IBPWn & RPM using the expression
{GM.IBPWn}*{SAE.RPM}/1200
If your IFR was set lower than actual, your cylinder airmass calculation will need to be out by the same percentage to get actual & commanded AFR into line.
If you right click on the pid & select more info the expressions will be shown.(Not all pids are supported in this manner though)

[joecar]

Yes, on the PIDs tab highlight the pid CALC.INJDC1 or CALC.INJDC2 and do rightclick->More Info.

Decreasing the IFR will cause the PCM to run the injectors open longer... IBPW and INJDC will still be correct, but the delivered fuelmass will be too much.

Like 5.7ute said, cylinder airmass (derived from VE or MAF) will have to be dropped by the same percentage to make the PCM calculate a smaller fuelmass which makes the injectors be open for less time.


This is for the initial IPW calculation on each cycle, before trims are added (trims are then added, combustion is triggered, and the trims are updated (for the next cycle))... this is ok for running in CL (trims correct to stoich), but this is not ok for OL or transients (the calculated IPW is wrong and no trimming).

[redhardsupra]

The curious property of IDC is that it is correct even while IFR is wrong. Joe and Mick are correct in stating that tuning with wrong IFR will result in overcompensation elsewhere.
AFR is a ratio of airmass and fuelmass. If you keep AFR constant, fuelmass must change. Fuelmass is a product of IFR and IPW. So if IFR goes down, IPW goes up, and vice versa. That's the overcompensation. IDC cares about fuelmass total, not IFR, one of its components, that's why IDC is correct regardless of individual components of fuelmass.