Delayed ref pulse (was Re: Spark latency correction)

[Ward]

On Mon, 20 Sep 1999 00:49:25 -0400, Shannen Durphey wrote:

> Ward wrote:
> > 
> > On Sun, 19 Sep 1999 17:26:29 -0400, Shannen Durphey wrote:
> > 
> > > Ward wrote:
> > >
> > > > Please remember that spark advance is actuall dely, since yiu cant
time
> > > > travel backwards to start spark, its actualy delay from the prior
TDC
> > event.

Fair enough, the delay is from the falling edge of the DRP to the falling
edge of the EST signal out of the ECM.

At 3000 RPM (5000usec) 1 degree of advance is 13.88 usec, since you have 90
degrees between events, 20 deg of advance will require a delay of 90 - 20 or
70 degrees of delay, or 972 usec fron the last DRP. 

The hardes thing for most people to get on to the idea that your doing spark
from the prior DRP. In truth you could be using the prior and timing from a
DRP 8 ot 10 cyl back. The limitation would be the engines ability to accell;
over comming its own polor moment of inertia.  This is a high value as
evedenced by the very high value of MAP observed when you stab a V8 that is
under no external load.

Ward

Off hand I can't think of a way to see this on a timing light.

Ward


> > > > to calulate a V8 time between TDC's do 15/RPM,
> > >
> > > I've tried to see this by routing the REF to EST and applying 5V to
> > > bypass.  I thought that I'd see a displaced timing mark with my
timing
> > > light, but it didn't happen.  What was I missing?
> > > Shannen
> > >
> > 
> > No. The delay in the processor won't be involved, and the inductive
> > discharge is also not in that loop.
> > 
> > When you put by pass to +5 you switch the DRP output ckt from the coil
> > driver to the DRP pin. You also disble the startup dwell and timing
advance
> > function. There is a 5 - 6 deg spark advance during by pass operation.
> > 
> > So I don't see how that would show the CPU indiced delay correction?
> > 
> > Ward
> > 
> Sorry, I wasn't clear.  I'm not looking for delay correction.  I'm
> trying to recreate a display which used a distributor, a 2 channel
> scope, and a coil to show the delayed pulse that timing is calculated
> from.  I don't remember an ecm in the display, but possibly there
> was.  I don't have the scope and I was hoping I could use a timing
> light.
> 
> The 89 Vette I was using showed no difference in timing, as viewed at
> the balancer, whether the ecm was running on base timing or ref pulses
> looped back to the EST terminal.  I expected to see retarded timing.
> 
> Shannen
> 





________________________________________________________________
Get FREE voicemail, fax and email at http://voicemail.excite.com
Talk online at http://voicechat.excite.com