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

Mon Sep 11 03:33:23 UTC 2006

Since we are on the subject of DIS ignition, how does the DIS on the
3.8L engine differ from that on say 3.1L v6?

I purchased a 89 Bonneville this weekend, and it's crank sensor is
mounted external to the engine, and reads teeth in the backside of the
harmonic damper.  (had to change it, rubber was gone)

Anyways, this 3.8L engine uses a different DIS module and coil pack
setup then I'm used to looking at.  The coils are all one assembly, not
2 towers per coil-pack.  Also, the crank sensor has two channels, a 3x,
and a 12x I think it was, can't remember.

Also, each slot in the 3x signal is a different length.

Anyone know how this system differs? Or had any experience with it?  Are
these motors sequential? (Reason for 3 different length slots on 3x
signal??)

-----Original Message-----
From: gmecm-bounces at diy-efi.org [mailto:gmecm-bounces at diy-efi.org] On
Behalf Of davesnothereman at netscape.net
Sent: Sunday, September 10, 2006 6:32 AM
To: gmecm at diy-efi.org
Subject: Re: [Gmecm] Modify $8D to work on MPFI 3.1L DIS engine

    The generation of Delco DIS related to that timing diagram uses only
crank information to synchronize the ignition coils. The coils, one for
each cylinder pair, are sequenced by the ignition module in a repeating
pattern initiated by the synch notch in the crank sensor. Both pistons
of each coil pair are at TDC simultaneously, with one ending the exhaust
stroke and one starting the power stroke. The coil provides spark to
both cylinders. One cylinder uses this spark to combust fuel, the other
does nothing with the energy.

 When the ecm isn't in the loop, the SA is 0 deg advanced. The reference
pulse is 60 deg advanced.

 I would have to say that moving the fire notches for a 4 cylinder
engine would likely advance timing, although there is probably a limit
to how far they can be moved before the module flags a problem. If the
synch notch is removed the module will stop providing spark and
reference signals and will do it straight away. 

 With only 2 notches on your crank, how do you determine which coil to
fire first? What safety is incorporated to prevent a sequencing failure
from ruining an engine? You'll need an additional signal of some type.
When the Delco DIS system was released there were not many ecm's in
production with the hardware or code to utilize a cam position signal.
Functionally the DIS replaces a distributor as a complete unit. With 3
variable changes in software, the distributor and DIS are
interchangeable. It seems like a cost effective design to me.

 With that in mind you might to wonder why, when the 2.0L OHC engine was
converted from distributor to DIS, GM decided to forgo the entire US
made DIS system. Instead they used the Euro / Bosch "extra tooth" crank
sensor and coils and a completely new / separate Delco ecm dedicated
specifically to an engine which would only be used for 2 years before
disappearing.

 Zaphod

 -----Original Message-----
 From: Robin at FuryWorld.fsnet.co.uk
 To: gmecm at diy-efi.org
 Sent: Sat, 9 Sep 2006 6:36 AM
 Subject: Re: [Gmecm] Modify $8D to work on MPFI 3.1L DIS engine

  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
>

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