7747 spark control questions.

[Programmer]

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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