Opinions wanted ( analysis of the effects of spark advance va riation on vacuum)

[cmillard at crutchfield.com]

Hi Bruce, 
I only changed the Closed throttle spark settings (not very scientific of me
- I'll do better next time.)
I let the PCM control fueling via O2s, IAC, etc, left VE alone, so I did not
have as much of a control group as I should have. 

My methodology (last nights tuning). I flashed the pcm, let car run 5
minutes, recorded 5 minutes worth of data, turned off, reflashed, started
again, etc... The temp was consistant 166F-173F.  I did not drive the car in
between flashes last night, as I ran out of time (Girlfriend needed company
:-)

I will repeat the experiment in open loop, disable the IAC (although the IAC
vacuum adjustments feel like they should be taken into account.) 

Cruising is the next step, baby steps I try to tell myself...

Hmm.. Plug gap.. I have a virgin set I can install at factory spec.. I'm
running 1 step colder due to 11.4:1 compression, I will go to stock
temperature if anyone feels that is a factor, I would like to avoid
detonation, and I know the colder plug always helped from my blown days..

Gotta run to a meeting (darn work..hehe)
Keep 'em coming (Thank You!),
-Christian

-----Original Message-----
From: Bruce [mailto:nacelp at bright.net] 
Sent: Thursday, September 21, 2000 11:17 AM
To: gmecm at diy-efi.org
Cc: Chipsbyal at aol.com; ewright at silverback.gorilla.net;
douglas.t.wood at lmco.com; jll at edge.net
Subject: Re: Opinions wanted ( analysis of the effects of spark advance
variation on vacuum)


Opinions wanted ( analysis of the effects of spark advance variation on
vacuum)
Did you disable the IAC, set the VE table so that for a given amount of
timing the fuel baseline was the same?. Over what period of time was all
this done?. How long was the engine run for temps to stabilize. Looking at
the BLs, seems like the pcm was affecting the outcomes, by being closed
loop.

I'd suggest repeating things with the above considerations. Nice to see
someone putting in the effort to really tune something and share the
results.

I've found that making cruise corrections takes the ecm 15-20 mins for each
correction to really take effect.

While timing is a big concern, remember it's really about recovering heat
energy.  ie having the optimum timing of when the reaction will be pushing
the piston back down.  So plug gap will have a rather large effect also (in
response to you using a .040" plug gap). Bruce




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