Re: P4 Cylinder Select Thanks

["nacelp" <nacelp@bright.net>]

Great info., now I can at least id the number of cylinders some "blank"
memcals I have are.
Grumpy


> I've just discovered how to select the number of cylinders in the P4 ECM
> hardware.  The number of cylinders is selected by the voltage on pin 11
> on the 34984 (aka 79435) chip.  This is U13 in a '727, '730, and '749.
> The pin 11 voltage comes from pin 56 of the MEMCAL.  This in turn
> connects to pin 13 of the 16 pin resistor network in the MEMCAL.
>
> Here's how the voltages are interpreted:
>   0 to 1   volt  : 8 cylinder port injection
>   1 to 2.5 volts : 6 cylinder port injection
>   2.5 to 4 volts : 4 cylinder port injection
>   4 to 5   volts : throttle body injection (any cylinder count)
>
> The '727 I tested this on defaulted to "4 cylinder port" when pin 11 was
> not driven (no MEMCAL).
>
> The CPU can read out the pin 11 mode selection.  Code 41 will be flagged
> if it doesn't match the cylinder selection stored separately in the
> MEMCAL's EPROM.
>
> --
> Ludis Langens                               ludis (at) cruzers (dot) com
> Mac, Fiero, & engine controller goodies:  http://www.cruzers.com/~ludis/
>
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