7747 related questions

[rrauscher at nni.com]

>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.
>

The fuel pump voltage input is read by the ECM. Some bin's
do an diag check on it, others don't. Depends on whether
the diag mask bit is set.

Here's the interesting part: The fuel pump voltage is used for
two functions. The first is for injector voltage compensation.
The other is to bump up the idle on a dropping voltage. Yep,
and I would have thought they would have used the BatV input
for this stuff.

BobR.

>> 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/
>
>
----------------------------------------------------------------------------
To unsubscribe from gmecm, send "unsubscribe gmecm" (without the quotes)
in the body of a message (not the subject) to majordomo at lists.diy-efi.org