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

Mon Sep 11 03:57:39 UTC 2006

hi,  the  early  model commdores   vn/vp v6 3.8 here in australia came  with 
the  setup where  all the coils are mounted in one block.

the later model commodres  vr - vt  v6 3.8 came with the  3  coils  , with 
two  towers on each  coil , like the ones your use to .

 both setups are 100 % interchangeable.
i`ve even swapped  one setup with teh other on my commodre.

mark k

----- Original Message ----- 
From: "Brendan Patten" <bpatten at centurytel.net>
To: <gmecm at diy-efi.org>
Sent: Monday, September 11, 2006 1:03 PM
Subject: RE: [Gmecm] Modify $8D to work on MPFI 3.1L DIS engine

> 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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