Roads are just starting to get dry up here and I am getting geared up to work on my tune. I have heard everyone talk about logging duty cycle and I am interested in this to see how my 44lb'ers are holding up and how much room I have left for a small shot of go go juice. There are so many different PIDs to choose from. Which ones do I want to log?

 

Log the injector pusle width, it will be in milliseconds. You'll compare that to the total possible time between power stroke events for a given cylinder - thats two revolutions - at a given rpm.

Just divide 120 by whatever rpm you log your pulse width at then compare to you logged values.

Example - 60 seconds in a minute @ 6000 rpms gives you 10 milliseconds per revolution times two revs per power stroke = 20 milliseconds. So at 6000 rpms, you have a maximum time slice of 20 ms to fuel the cylinder. 60/(rpms)*2=120/rpms

My example:
I can log 23 ms pulse width at 6000 rpms, so my PCM is saying it needs 23 ms to supply the desired amount of fuel. 23 is 115% of 20, so I'm at 115% duty cycle and lean.

This means that the higher you spin and more power you make, the bigger the injector you'll need.

 

so is there a generic injector pulse width PID, or is there a PID for each injector?

Then, how do you make the next connection from: "I'm at 115% duty cycle and lean," to: I need more injector, or I don't need more injector?

Thanks, TEX.

 

EFI has a PID for injector pulse width, but I don't know its exact name right off hand.

If the total possible time to add fuel is 20 ms and you are logging a higher value, then you are out of injector. 23 / 20 = 115% - I was saying my PCM is commanding 15% more fuel per cylinder at 6000 rpms than my injectors can possibly flow.

 

ok got it. Sorry for my stupidity. Thanks TEX

 

my efi live has an actual injector duty cycle pid to choose from.

i was at 108% with the stock injectors and with the 57's the most i have seen is 42%, got some room to grow there.

 

INJDC% = INJBPW * RPM / 1200 (condensed version of the math Tex showed above)

Wow! 57lbs injectors are pretty big parish!