Mallett396

On my stock Silverado SS, I normally see the Injector Duty cycle move upto 98% around 5700 rpm @ WOT.

I have scaled my IFR table to lower my LTFT's to bellow 0.

Basically, I want to confirm, that adjusting the IFR table will not skew the reported Injector Duty Cycle in EFI Live. Can anyone confirm, or deny?

Also, at what point, should I start looking at new injectors. I'm guessing during my next real mod? Cam maybe.

Thanks

red ws6 99

Yes if you set the IFR wrong then you can scew the duty cycle.

First you can't look at duty cycle without knowing what your air fuel ratio is at the point. The AFR must be determined from a wideband. So you compare your actual afr to the commanded afr (what you get from efilive or autotap). If your actual afr is more rich than commanded then get those in check. Once they are in check then check the duty cycle. You should not run your duty cycle above 80% (again based on your commanded/actual afr). You could see a 100% afr but only because you are getting 11 afr and commanding 13 afr. Anything above 80% can damage the injector.

Gary

deezel

Disclaimer: just my opinion/understanding of how the PCM works

The injector duty cycle is calculated from RPMs and the base pulsewidth determined by the PCM (INJDC=INJBPW*RPM/1200). The PCM determines INJBPW from VE, IFR, PE, MAF, MAP and probably a few others. It does not matter what your AFR is, the injector duty cycle ONLY depends on INJBPW and RPM.
IFR seems to have a direct effect on all fueling. If you trick the PCM into thinking the injectors flow more or less, then it will compensate by changing the base pulsewidth.

I also see about 98% INJDC with my stock injectors around 5600. It actually starts to drop after that - down to about 95% around 5800. Sounds like we both need a cam for more air flow and bigger injectors for more fuel.

jimmyblue

iTrader: (11)

It should affect it initially and open-loop but learn it
back out in closed loop (the point of doing it, to get
your LTFTs to move). The closed loop PW will servo
back to where you started once the trims accumulate
fully.

red ws6 99

I give an example from my car. First its a Incon twin trubo running 9 psi. I have 50 lb injectors. For the tests to see what effects PE have on injector duty cycle the following are left the same: boost level, timing, ifr, fuel pressure.

So I set the PE to 1.34 which gives my AFR of about 11. Maximum injector duty cycle was 68%. Changing only the PE to 1.23 gives an AFR of 12 and the duty cycle drops to 50%.

Why does the injector duty cycle drop because you have told the computer to run leaner which means less fuel, which means less injector on time.

Gary

deezel

I agree on how the PE table works. It has a direct effect on WOT fueling. The original question was about the IFR (Injector Flow Rate) table and if it would change the calculation of injector duty cycle.
You said...
My point was that the injector duty cycle can be determined at any time if you know the base pulsewidth and rpms, and that changing the IFR table does not affect the accuracy of the injector duty cycle calculation.
I also agree that the commanded AFR from the PCM is not accurate.
Knowing the injector duty cycle without having accurate AFR values can still be useful information. For example, my relatively stock truck seems to be running out of injector, as does Mallet396's. I have been tuning using my knock sensors, so my AFR is probably not ideal. But, I know that my injectors are running too high during WOT runs.
Hope this clarifies things...

red ws6 99

Sorry, obivously was not reading to closely. I agree if you have duty cycle that are high you are running out of injector.

Gary

deezel

Hey, its cool. Sometimes I'm not clear or detailed enough... I was at work when I made the first post and I just whipped out a quick reply...