7747 related questions

[Ludis Langens]

Ross Myers wrote:
> 
> 1 - On the wiring schematic there is shown a "Fuel Module" for the 7.4L and
> 5.7L models.
> It connects to B2,

Well, pin B2 is where the ECM measures the "12V" voltage being sent to
the fuel pump.  I don't know if the '747 checks this or not - but in
general an ECM could use this input to detect problems with the fuel
pump relay.

> 3 - Can the 7747 be run without the Calpack in it?, the ECM's he got were
> from a 4.3L, so I 'guess' it won't run too good if we put a 7.4L EPROM in?.
> He doesn't care about limp mode (hence the 2 ECM's), so if the 7747 looks
> for a No_Cylinders voltage from the calpack what should I use for a V8?.

I theorize you can get it to run without the CALPAK if you add a jumper
resistor.  The ECM supplies 5V to pin 16 of the CALPAK.  The ECM
software measures the voltage at CALPAK pin 12 to determine if the
CALPAK is missing.  There's a 10K pulldown on the ECM side of this pin. 
You need to overpower the pulldown - I've seen GM use a 1K resistance in
the CALPAK for this purpose.

Pin 11 of the CALPAK tells the limp home circuit that the CALPAK is
installed.  This is yet another pulled down pin.  I think you can leave
it open - thus turning off limp home mode.

Pin 8 of the CALPAK enables the seperate firing of the two TBI
injectors.  With pin 8 open, they'll both fire simultaneously.  With pin
8 pulled to ground (available at pin 7), they'll fire seperately.

Because the '747 is a TBI ECM, it doesn't care about the cylinder count.
 The only problem I can think of is starting.  I don't know if the limp
home circuit gets involved in starting or not.

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


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