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

[Robin Handley]

Thanks.

Robin

----- Original Message ----- 
From: <davesnothereman at netscape.net>
To: <gmecm at diy-efi.org>
Sent: 10 September 2006 12:31
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