870 Spark Control

[Keith D. Miller]

20 degrees is the max retard for an ESC module, have you checked to be
sure
the ESC or wiring is not bad, signaling the ECM to retard?

Keith
--
  -----Original Message-----
  From: owner-gmecm at diy-efi.org [mailto:owner-gmecm at diy-efi.org]On
Behalf Of Matt Sandine
  Sent: Friday, May 11, 2001 3:47 PM
  To: gmecm at diy-efi.org
  Subject: Re: 870 Spark Control


  I am not kidding. It bucks and sputters all over the place, but that
is what is really happening. You can tell the fuel is totally being
ignited at the wrong time. I thought my timing light could be way
outta wack. I used another with the same results. She purrs like a
kitten when the timing connector is disconnected and it is at 6 deg,
besides the fact that you can't rev it because the computer isn't
adding the spark. Just in case the balancer was slipping, I marked the
pulley. It is honestly retarding the spark at least 20 degrees from
the 6.
  Does this make sense? The only way I have been able to figure out
spark advance on the 85 (since it doesn't show it in scan tools)
besides using a timing light is to use a scope on the pickup coil
input and EST output at the computer harness. By tracking both of
these waves at the same time, I was able to see the EST get tighter
and tighter compared to the pickup coil pulse remaining constant. Only
problem is, I need to try to figure out if the EST pulse is actually
being retarded from the computer or if it is being retarded at the ESC
module. Thanks for the interest Lyndon, -Matt-


    Matt,

    If this thing was going into 24 degrees retard from 6 BTDC, it'd
stall. Are you 100% sure it's going 24 ATDC ?

    Lyndon.

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