sequential efi on 440?

[TBK]

It's my understanding (and oh great one is going to correct me on this, I
can just feel it), that spark is used to control the idle as much as airflow
in the GM FI engines. I watched as the timing would jump around like mad.
Finally, that's what I learned.

I'm running a .440" in/ex 212/12 duration cam and the idle is steady with
tons of lope in my 2.8L V6. About 14 in of vacuum. Passes smog fine, but
raises the eyebrows of the inspector.

TK
-----Original Message-----
From: bruce plecan <nacelp at bright.net>
To: diy_efi at efi332.eng.ohio-state.edu <diy_efi at efi332.eng.ohio-state.edu>
Date: Thursday, January 29, 1998 9:12 PM
Subject: Re: sequential efi on 440?


>Ref the idea of a stored vac..  Tried that with a series of
>restrictors to the map, and then with fixed volume dampners
>and restrictors, to no avail (spent lots of time, and effort)
>then tried a series of TPS steps with voltage dividers
>to tamper with the map signal.  Even with V steps as little
>as .07v of tps, drivability was notchy.  IMHO the ECM looks
>for a increase of O2 v when it momentarily richens mixture,
>if it doesn't see this then it starts hunting with timing.   It's
>real easy to wind up with an errattic idle.  If someone has
>all the answers about what the ecm is doing at idle I'd love
>to hear it.  It is a real balancing act of timing mixture, and
>IAC.  It also has some sort of stall antisapator(?), so that
>if it thinks the engine is going to stall it takes measures to
>prevent that.
>The above is just what I've noticed, with a 747 ecm, and
>big cam.
>HTH  Bruce     Where would we be without cone shaped
>                        hats?.
>