P4 Cylinder Select

[Ludis Langens <ludis@cruzers.com>]

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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