7747 spark control questions.

[Shannen Durphey]

That's it!  : )

And now you see why I say that 9 degrees base timing does not mean
that the timing is advanced 9 degrees.
Shannen

Programmer wrote:
> 
> OK--I see the problem. There's confusion between the "initial"
> spark value number and bias spark value.
> The '89 454 bias is 4 and initial is 4 deg.
> An '89 5.7L is initial "0" and bias "10".
> 
> Lyndon.
> -----Original Message-----
> From: Shannen Durphey <shannen at grolen.com>
> To: gmecm at diy-efi.org <gmecm at diy-efi.org>
> Date: October 17, 2000 5:25 PM
> Subject: Re: 7747 spark control questions.
> 
> >Here's an example of exactly what I meant.  ANTZ8364, 89 3/4 ton
> >w/454.  Base timing 4deg BTDC, base timing value in ECM, 4 deg.  That
> >way the timing values in the table reflect timing at the engine.
> >BTW, I placed antz8364.bin in incoming.
> >Complete specs:
> >ANTZ8364  1988 3500, RVCK, 454, 4SPDMAN, 3.42/3.73 REAR GEAR, 7747ECM
> >Shannen
> >
> >Programmer wrote:
> >>
> >> >>Does the bias not reflect what the distributor initial timing should be
> >> set
> >> >at?<<
> >> >
> >> >All the timing decals I've seen are "0" EST bypassed.
> >> >
> >> >>Why would you have a value like this unless it was just for something
> like
> >> >ALDL output?<<
> >> >
> >> >I don't recall even seeing a spark value on a scan tool for a 7747 truck
> >> >app. Tech 1 maybe ?
> >> >
> >> >>> You could just add 10 degrees to the timing tables and set the
> >> >distributor at 0.  No need for subtraction in the timing table<<
> >> >
> >> >Well---that's how I thought it was.
> >> >
> >> >What is the raw value for the 50kpa at 600rpm?
> >>
> >> Oops...hit the enter key <g>.
> >>
> >> Just checked a 1989 SWB Chevy with a 5.7L auto 7747 equipped.
> >> Base timing is "0" BTC with the EST disconnected.
> >> 30 kpa @ 1000 rpm (cold) measured timing is 43 BTDC.
> >> 34 kpa @ 800 rpm (cool) measured timing is 38 BTDC.
> >> --Got interrupted when some freight showed up--
> >> 32 kpa @600 rpm (70C temp) measured timing is 22 BTDC.
> >>
> >> And no--I did not use the diagnostic mode on the scanner which bumps up
> >> the timing. TC's tables appear to be bang on...Winbin's you need to
> subtract
> >> the bias value.
> >>
> >> Lyndon.
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