747 Timing Connector and misc questions

[Bruce Plecan]

-----Original Message-----
From: Jason Weir <jweir at worldnet.att.net>
Subject: Re: 747 Timing Connector and misc questions


>Shannen Durphey wrote:
>
>> Actually what I intended to say is that the timing advance
>> you are seeing with the bypass disconnected is built into
>> the module.  Once the bypass line is opened, the ecm cannot
>> control timing.
>
>Ahhh, I see now, the ESC mod controls it after the connector is undone.
Clears that right up...

No, no, no

The ESC is for retarding the timing due to knock.   It sends a signal
to the ecm when knock is detected.  The ecm then retards the timing.
the ESC is the thin black box about 2"x2".  All it does is listen to
the knock sensor.  When it hears the right noise it tells the ecm hey
we got knock.  Trouble with this system is that certain sounds sound
like knock, and can falsely trigger it.

With the timing connector disconnected (tan/blk wire) the ecm has
no control over the timing.  The only timing is what is inherit with
the actual design of the electronics.

When you rev a ecm timing controlled car in neutral (gm ie 747) the
timing curve you see with a timing light has nothing to do with what
you have in gear, or when driving the car.  The timing curves you
have posted have notthing to do when the car is in gear, or when
a vss is present.

The only real good for accurate timing a timing light does on a 747
is setting base timing, ie tan/blk wire disconnected and speed below
800 rpm.

>Jason Weir - 88 YJ - 258 / Howell TBI  145K and counting

Cheers
Bruce