Tailor made patches?

[rr]

Ludis, Thanks for the tips, definitely some good ones. As for
the rpm limiting, I've noticed that some '747 bins tapered the
VE% off quickly at high rpm. I kinda' figured that this was
done to limit rpm & power.

I've looked at the code and have two methods that I am
going to try for the mph limit.

BobR.

Ludis Langens wrote:

> rr wrote:
> >
> > (yep on the sub, have'ta to do a couple of calcs, and return
> > with the results.
>
> You probably don't want to use JSR/RTS.  That'll need two extra bytes of
> stack space.  The C3 ECMs tend to be very tight on stack space.  Many of
> them even have a subroutine that pops off a known return address and
> replaces the RTS with a JMP to that address - this saves two byte of
> stack RAM.
>
> Also, the code patch will need to go to two different places:  Back to
> the original code, or elsewhere for fuel cutoff.
>
> In C, the patch is:
>
>   temp = 85;
>   if (speedLimited)
>     temp = 83;
>   if (vehicleSpeed > temp)
>     {
>     speedLimited = true;
>     injectorPulseWidth = 0;
>     goto FuelCutoff;
>     }
>   else
>     speedLimited = false;
>
> It looks like the '747 doesn't have a rev limiter.  If it did, the label
> FuelCutoff could be in the rev limiter cutoff code.  Perhaps the
> DecelFuelCutOff would have a location with the correct functionality.
>
> > Been lookin' at the code, might have to
> > steal room from the egr tables, others aren't so large).
> >
> > This is one drawback with this ecm, it doesn't have any
> > extra room in the eprom.
>
> There is some space in the transmission tables.  If the truck has an
> auto, the manual transmission tables are unused.  If the truck has a
> stick, there is even more space in the auto tables.
>
> If the '747 EGR is at all the same as the Fiero V6, there might be space
> at the tail end of the "EGR to injector pulse width" table.  The Fiero
> uses only the first five out of 16 or so bytes of this table.
>
> Instead of patching the '747 code, how about using an ECM which already
> has a speed limiter?  The 1228746 (passenger car 5.0 & 5.7 TBI) does.
>
> --
> Ludis Langens                               ludis (at) cruzers (dot) com
> Mac, Fiero, & engine controller goodies:  http://www.cruzers.com/~ludis/