7747 spark control questions.

[Shannen Durphey]

Programmer wrote:
> 
> Ok, EST bypassed is non computer dizzy timing. You should then be at TDC or
> 0 degrees as per the timing decal. If Bias warm is 10 deg. Bias
> cold is 20 deg (I think). Winbin table for 50 Kpa @ 600 rpm is 29.88 deg
> whereas
> Tunercat is 20.1 degrees BTDC. (Using an ARJT as an example).
> Winbin adds 10 deg or includes the bias--TC doesn't add it-- so what's the
> actual "engine" measured timing value at 50Kpa and 600 RPM ? I'm assuming if
> the WOT table has a negative, it's adding 10 bias. So lets' say we have a
> negative 3 at 100Kpa and 1000 rpm--we've got an actual 7 BTDC at that point
> provided we set the ignition timing as specified. If we add 9 degrees to our
> base timing, we've then got a physically measured16 BTC at 100Kpa and 1000
> rpm. Is this not correct ??

If you add 9 degrees at the distributor and do not change any prom
values, you've advanced the timing at the crank by nine degrees.  If
your distributor is set at 9 degrees, and the value at 0x009 is 9
degrees, the position of the distributor is adding no more timing to
the ecm calculation.  The ECM calculates desired timing based on
tables, warm n cold spark bias values.  Then the ECM subtracts the
initial distributor setting from the final calculation to deliver the
correct timing.  

Base timing, bypass timing, non EST timing (all the same) affects
startup, specially hot, limp home driving, stall recovery, minimum air
setting, dieseling (Yep, it can happen w/TBI).  Most of us set it -n-
forget it.  The initial distributor value is a means to allow the base
timing to be set at your choosing  The spark tables will reflect
accurate timing.  You pick the timing value that you want, and the ecm
takes care of remembering where the distributor base timing is so the
timing at the engine is the timing you've set in the tables.

So you can have 9 degrees advanced base timing, and nine degrees in
static timing value in ecm, and they cancel each other out.

Shannen

> 
> 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 10:41 AM
> Subject: Re: 7747 spark control questions.
> 
> >Depends on reference or initial timing value at 0x009.  If bias is at
> >10 Dizz base at 9, and static angle is 9, spark table is only 10 deg
> >biased.
> >Shannen
> >
> >Programmer wrote:
> >>
> >> You're at 9 BTC with the EST disconnected ? That adds another 10 with
> >> EST connected. You're going to be close to 35-40 BTC hot idle.
> >> Lyndon.
> >> -----Original Message-----
> >> From: Reid Bishop <rbish at ibm.net>
> >> To: gmecm at diy-efi.org <gmecm at diy-efi.org>
> >> Date: October 17, 2000 12:52 AM
> >> Subject: RE: 7747 spark control questions.
> >>
> >> >>>Dissies are set "0" with the EST disconnected. The bins should show
> main
> >> >>>spark bias at 10 degrees.
> >> >
> >> >Really?  Hmmmm... my 4.3 dist is set to 9 BTC, and I my spark bias is
> set
> >> to
> >> >10.  I could still use more advance throughout the curve, but not
> working
> >> >that yet.
> >> >
> >> >Are 4.3's the exception to this rule?
> >> >
> >>
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