Injector Offset from Flow Data

[jimmyblue]

I found a web page which had coherent injector static
and pulsed flow (2.5mS/10mS) numbers. I worked these
over in Excel and it appears to produce sane time-offset
values. I am curious whether anyone here has "backed
into" injector offset table numbers, for any of the listed
injectors, and how their results compare.

This data does not come with info on the drive voltage
and the fuel pressure is 300kPa, not 4 bar, but it seems
to bear out my notion that offset values -could- be
obtained empirically.

It is interesting that there seems to be no real trend by
volume or make, to the offset.

<attached .xls>

I've got another "charity tune" coming up and I could use
some proven-good 42# Lucas tables.

[S2H]

hey jimmy...I did a 2000 camaro with lucas 42's...
I jujst used the injector spreadsheet....and it came out great...
I had previously tuned the car cause it was mine....and guy froma local board bought it from me....
he changed injectors to get ready for some superchargin...and he put lucas 42's on it...
all I dis was change the injector IFR table and all his rims were still within +/-4..except for a few down at idle that went -6/-8
and we did just a hair of WOT correction...it didnt take much...
I was really amazed at how close it was

I'm sure that I could have played with it a little and gotten the offset volts to make them all fall back in line...but teh offset table from the 2000 camaro was close enough...

[redhardsupra]

Jimmy,
i'm really interested in this, i can see what you're doing with your math, but i'd like to know where the logic comes from. care to elaborate?

[jimmyblue]

The way I make out the injector offset as used by the
PCM, it's a pulse width adder to correct for actuation
time. It's how much pulse you can apply and still get
zero delivered fuel, pretty much.

So I take the 10mS/10mS (static) flow, and the 2.5mS/10mS
dynamic flow, and extrapolate to the zero delivered fuel point
(X-intercept) which gives me a negative time value and which
the addition of a positive injector offset, would put to zero
fuel at zero "desired" pulse width.

This all seems nice, in theory, but now I'm looking for some
real-world confirmation (not to mention any idea at all, of
the test conditions underlying the table; system voltage
in particular as that goes straight to current ramp time
and time-to-delivery).