Re: 7749 question

["Green" <green@dsl.telocity.com>]

> > In the SyTy 7749 ECU fuel control scheme, where does the Injector Flow
> Rate
> > enter into the BWP calculation equation?  There's no mention in the P4
> > document of this term; there's the BPC term, which supposedly
compensates
> > for engine displacement & injector flow rate (& EGR).
>
> I'm not sure what the injector flow rate is used for.  I'll edit that
> sometime when I have my emulator hooked up and see if the a/f ratio is
> affected.
>

It isn't in the code at all, so I'm guessing it isn't used in the fueling
calculation at all.  I've had some chips that i changed it in, others i
didn't, no difference between them.

> > Reason I ask is that I'll be changing to some 40#/hr injectors from the
> > stock 29#/hr flowrate and I'm wondering where to input this new info for
> > the ECU to "see".
>
> Sounds like an opportunity to finally get some good data for a 40# chip.

course it will be on a truck running an Isky cam and Vortec heads

> >
> > Promgrammer has data fields for both terms, one a Gal/Hr injector flow
> rate
> > constant and the F28 table of BPC vs EGR.  Value here is .108 across the
> > board; larger injectors would mean changing this value to what?
Inverse?
>
> I ended up using .059 across the board for the MSD 50# injectors.  I think
> this could vary +- .010  depending on the values in the f29 and f30 tables
> and the fuel pressure you are running.   An educated guess would put you
> around .084 for the 40# injectors.
>

Stock is .089, I had to multiply by 1.5 for 3 bar, giving you .1335, i went
leaner (.108) to adjust fuel curve for elevated fuel pressure.  Simple calc
to give you F28 value to start with :
.089 stock x 1.5 = .1335     then  x (30/40 )  =  .100

> Some other things to play with include KAPLL, KAPLH, KAPMIN, F31, F38, and
> F92 tables.

To give you accurate values for these (BPC as well) the best way to do it
would be to get injector pulsewidth versus fuel delivered data.  You could
find out at what pulsewidths the injector loses linearity, when it delivers
no fuel etc.  Also could compare to stock injector data, to get a slope of
the line to adjust BPC correctly, adjust the F92 offset based on that data
also.  Problem I found doing this is that the stock chip does not have any
values for the F94 table, and I believe that it should, from looking at
stock injector data..  Also, the F94 table is a bit limited.  It doesn't
extrapolate off the end of the table (if pw is greater than 3.9ms, offset is
set to zero).  So if you wanted to do that table the same way most timing
tables are done (with positive values in all tables, decrease value to
'subtract') it isn't possible.  Between the F92, F94 and F28 you *should* be
able to have an injector dialed in very close to stock (forgetting about AE
right now), but I found this wasn't possible (for me at least, and the
injectors i tried).

The quasi-asynch fueling can get sketchy, not sure if it's fault of the
design of the fueling, or calibration, but when i've tried running the
quasi-asynch at less than XX ms, I had problems at the transition spots ...
I have a few chips that run full quasi-asynch, runs fine... I haven't seen
any issues running the injectors this way.  Kinda like running bank to bank
rather than batch, as the injectors are only firing once every other
rotation.  Good for idling bigger injectors.

>
> I haven't looked at the aftermarket 40# chips, but I believe the major
> change was to the BPC only.

No... the ones i've seen didn't even do that. Changed injector flow rate...
but my guess is they had some documentation on the chip, and saw injector
flow rate, and assumed it was injector constant.

Brian Green
Syclone #160


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