Main spark bias

[Shannen Durphey]

WEG1192 at aol.com wrote:
> 
> Can anyone tell me if the term "main spark bias" in the Tunercat 7747 ECM
> constants tables is the same as the "spark reference angle" in the GMEPRO
> tables? In my stock 7747 truck bin, the main spark bias is set to 10, but I
> thought the base timing setting was 6 deg for GM engines.
 
Spark bias is not spark reference angle.
Base timing is 0 degrees for most truck engines. 

> 
> Also, can anyone shed any light on how open loop tuning is affected by the
> closed loop tuning. I am tuning a 7747 to run an AMC 360 engine. I have added
> almost 40% more VE to the RPM vs. MAP table in most locations and it still
> isn't enough, but its close. But it won't run well until it gets to closed
> loop mode, so I was wondering if I need to tune the open loop first. I guess
> I don't understand the relationship between the open loop tables and closed
> loop tables. Is the ECM still using the main fuel table in open loop, but
> just adding an A/F ratio multiplier to richen the mixture a little? Can
> anyone tell me where to find info on open loop tuning or remember a
> discussion in the archives? I've searched but no luck so far.
> 
> Thanks for your help. I'm tuning my first motor and it is challenging to say
> the least.

Are you beginning to realize why "just do it" gets thrown around so
much?  Tune for "very close" in open loop, and the ecm will need to
provide less correction in closed loop.  The engine should run
acceptably well in open loop.  Closed loop is really to make the
catalytic converter happy, not the driver.  It should not be used as a
crutch for a kinda close open loop calibration.  IMO, for relatively
stock engines, the injector size, fuel pressure, and base timing
should be close enough so that "back up fuel mode" still provides
reasonable performance.  But YMMV there.  

Have you been saving email?  Bob Rauscher (rr) has posted some
excellent stuff, there is info on closed loop disable in programming
101, and I think there's a text file in /incoming that discusses
this.  There have been discussions about this recently, and they're
good ones, too.

Shannen
----------------------------------------------------------------------------
To unsubscribe from gmecm, send "unsubscribe gmecm" (without the quotes)
in the body of a message (not the subject) to majordomo at lists.diy-efi.org