Novice Question

[Ludis Langens]

Bob Valentine wrote:
>
>          The number of cylinders is selected by the voltage
>         on [...] pin 13 of the 16 pin resistor network in the
>         MEMCAL.
>
> Hmm....   So can you just pull pin 56 of the memcal to ground?  Might try
> disabling code 41....

Pulling it to ground should work, but note, the knock sensor filter will
be incorrect.

Code 41 is caused by a mismatch between this MEMCAL generated voltage
and a value in the EPROM.  If you are using 8-cyl software in the EPROM,
grounding the pin will make code 41 go away.



Peter Gargano wrote:
> 
> I'd assume you could "just pull it to ground"
> although, for current consumption reasons, I'd be measuring the value that
> a "normal" 8 cyl netres uses, and use that!

Good suggestion.  I generated the voltages using a 5K pot and had no
voltage drop problems - implying that the load is high impedance.



You can check the '7749 schematic on my web page to find which MEMCAL
pin(s) is ground.

It might be a good idea to try to disable limp-home at the same time.  I
have a hunch that MEMCAL pin 45 (pin 7 of the 14 pin network) is the
enable/disable for this.  The ECM has a 10K pullup on this pin.  With
the MEMCAL missing, the limp-home chip stays mute.  I suspect that the
MEMCAL pulls this pin low to allow limp-home.

-- 
Ludis Langens                               ludis (at) cruzers (dot) com
Mac, Fiero, & engine controller goodies:  http://www.cruzers.com/~ludis/

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