[Gmecm] Modify $8D to work on MPFI 3.1L DIS engine

[Robin Handley]

Been studying the DIS timing diagram.

Apologies for my dumb questions (I've never really looked very closely at GM
DIS before).

1) Is there still a rotor arm to distribute the spark to the correct plug?
If not, how is this done? Is there still just one coil (I know some DIS
systems have 2 and fire 2 cylinders at the same time - but that still
requires cam phase knowledge, to know which 2 to fire.)

2) When the ECM isn't in the loop, with the DIS system, is the SA 60deg?

3) AIUI, a _dizzy_ (reluctor) trigger generates a pulse via the HEI module
to the ECM when any cylinder is at the static advance position (e.g. 10deg
BTDC), defined by the rotation of the dizzy mounting. So, when the ECM is
out of the loop, the HEI module fires the coil straight away - which gives
10deg SA. I'm not sure whether the pulse from the HEI module to the ECM is
high to low or vice versa. Assuming high to low, then it is equivalent to
the 60deg BTDC trigger from the DIS. So, what if notches 1 & 4 on the DIS
trigger wheel were moved to be 10deg before notch 5? Would this resync the
DIS module? Why is the logic of the DIS module needed (i.e. can't the raw
trigger go straight to an HEI module, like the dizzy one, so you'd just have
2 notches on the wheel)? Is the answer to this related to the answer to 1)?
:-)

Thanks,

Robin

----- Original Message -----
From: <davesnothereman at netscape.net>
To: <gmecm at diy-efi.org>
Sent: 04 September 2006 12:51
Subject: Re: [Gmecm] Modify $8D to work on MPFI 3.1L DIS engine


> On a 4 cylinder engine the "double notch" of the 7x crank wheel indicates
synch.  The module fires on the next signal from the crank wheel.  Two
pulses are counted and the module fires on the third.  One pulse is counted,
then the double notch to indicate synch, and the cycle begins again.
>
> Zaphod
>
> -----Original Message-----
> From: Robin at FuryWorld.fsnet.co.uk
> To: gmecm at diy-efi.org
> Sent: Sat, 2 Sep 2006 6:46 AM
> Subject: Re: [Gmecm] Modify $8D to work on MPFI 3.1L DIS engine
>
>
> > On Friday 01 September 2006 04:31, Robin Handley wrote:
> > >
> > > I hadn't thought about the cranking situation, but I'm now wondering
how
> a
> > > DIS based ignition system can actually get an engine to start (when
the
> > > 'static' advance is so far away from something you'd want to use for
> > > cranking). Does the DIS module do something clever here, that I'm
> missing?
> >
> > Nope, when cranked (when the ECM is *not* controlling the timing), the
DIS
> > module just fires the coils at the crank mark timing (the static timing,
> > typically of 0deg), and only the signal it gives back to the ECM has
60deg
> > offset.
>
> Sorry if I'm being dim here; when the ECM is not controlling the timing,
> does the DIS module fire at every pulse from the trigger wheel? How does a
6
> x 60deg trigger wheel work for a 4cyl engine?
>
> Thanks,
>
> Robin
>