'7747

[Shannen Durphey]

Are you interested in using a 7747, or an 8746, or???
The information for both ecms is available.  Are you planning a swap from one ecm
to the other?

Ken Kelly wrote:
> 
> Hi guys, I'm new to the list - I've talked to Bruce a few times in private
> and I decided to join up here and ask my questions so I wouldn't bug him as
> much. :)
> 
> I've got a few simple (I hope) questions about the '7747 that I'm hoping you
> guys can answer. I've been reading the schematics (of the '8746, which is
> supposed to be similar?) on Ludis' website and checking out all the inputs
> and outputs, comparing them to the pinout page. I wanted to know what some
> of them are;
> 
> 1. C8;PSPS - what the heck is this? (Power steering?) What does it do? How
> does it work? (It's labelled as an input..)
closes when power steering system is pressurized.  Consider it a load sensor to
help prevent stalling.

> 2. A2;A2OUT - listed elsewhere as "A/C Control" .. how is this wired in with
> the A/C? What does it do? Are you supposed to wire your A/C switch into the
> ECM, and the ECM to the compressor (so the ECM controls the compressor?) I'm
> only assuming that it cuts the compressor off at higher throttle settings so
> you get more power? (y/n?)

It's not used in all applications.  If you're installing a 7747 in a system with
"self contained" a/c, it's not necessary to connect this.  Although it might be a
nice touch to make a "professional" job out of it.


> 3. C2;SELECT - I'm hoping/assuming that this is the A.I.R. select valve;
> meant to select between the cat and the header injectors.. am I wrong? Is
> there anything special to enable this or does it just "work"?
> 4. C1;DIVERT - Same as above, but to divert air from the SELECT valve to the
> air cleaner (during deceleration, so you don't get backfires) Correct?
> (y/n?)

IIRC  C2 is exhaust/atmosphere and c1 is c2/converter.

> 5. A3;CAN - Cannister purge?
Yes.

> 6. B6;VATS - is it even used on the '7747?
No.

> 7. C12;MAT - Manifold air temp.. is it used either?
No.

> 8. B9;B9IN - What is this for? Says "Not used" on the pinout schematic.
Not used in that application. : )
You might want to look at the links on this page:

http://www.diy-efi.org/gmecm/ecm_info/

If you haven't already found it, there are wiring diagrams there for both ecm
types.
Shannen
> 
> I appreciate any and all answers!
> 
> Ken
> 
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