[Gmecm] TBI Swap - Iron Duke Tech IV

[Dustin Lof]

OK I just read Jays post, lets say we take the donor
olds 2.5 DIS car, it is a fully functioning driveable
car, lets unplug the four wire connector at the
ignition module, the one that leads to the ecm.  Days
later we forgot that we unpluged that and try to start
the car, what happens- it doesen't start, lets
troubleshoot, we start by listening for the fuel pump
when we turn the key on, yep that runs, now we take
the air cleaner off and plug in our noid light, crank
the engine, no light, we better check for 12v at the
injector, yep that fuse is good, let check spark, good
spark, wait a minute did you say good spark, why yes,
the ignition module converts the 6+1 pulses the crank
sensor generates in to a signal with 4 pulses spaced
90 deg apart this signal goes two places, one we like
to call primary ignition (when not in est mode).  The
second we call reference it is outputed to the ecm. 
The module also dictates which coil fires on what
pulse, it does this using the +1 pulse from our 6+1
signal generated by the crank sensor.  

So now we have a reference signal, a four pulse (per
crank revolution) five volt square wave, the same as
an older version of the same car using a distributor. 
The functions of the four pins in the four wire
connector of the distributor is exactly the same as
the DIS module. I would bet that the electrical
connector is the same.

The only hang up, like Jay said is changing the base
timing ofset in the chip to make the tables come out. 
so changing to an ecm like a 7747 wouldnt be a bad
idea.  

The distributor I am refering to is the style using an
eight pin ignition module, small cap, push on rotor,
external coil, single pickup.  I posted a picture on
the ftp its called 2_5 distributor.jpg
ftp://ftp.diy-efi.org/incoming/   there are 2.5s with
dual pickup distributors, mostly in S10 trucks, they
look similar but if you look close, there are more
wires.  
--- Jay Vessels <jay at vessels-clan.com> wrote:

> Hi there!
> 
> There's lots on this in the archives, and I
> (obviously) need to go do
> some reading, but I'm a bit confused about why this
> (triggering DIS ECM
> with a distributor, or vice versa) won't work on the
> TBI case being
> discussed (or for MPFI systems either). I'll quickly
> concede that SFI's
> a different beast.
> 
> Let's use a V6/60 like the 2.8V6. The distributor
> will generate one
> pulse per firing event, spaced 60 degrees apart.
> This goes to the ECM,
> which then modifies the signal and sends it back to
> the EST module to
> fire the plug. Still, the signal from the EST is one
> per cylinder, all
> 60 degrees apart. These pulses to the ECM do not
> change with ignition
> timing.
> 
> The DIS is similar on this engine family. The ICM
> sends a pulse to the
> ECM once per firing event, spaced 60 degrees apart.
> These pulses to the
> ECM do not change with ignition timing.
> 
> I *assume* for the 4 cylinder case that the ICM
> generates one pulse
> every 90 degrees, just like the distributor. If not,
> that could be a
> show-stopper (since the distributor puts out a
> different pulse train)
> but I'd be surprised if the DIS for the 4-cylinder
> did that.
> 
> The only difference appears to be the reference
> angle for the firing
> event. The ICM (in the V6 case, anyway) is
> referenced at 60 degrees,
> and the distributor is referenced at 0 degrees. For
> an application
> using a distributor to trigger an ECM designed for
> DIS (i.e. 1227730
> running $A1 for MPFI), couldn't the distributor just
> be installed at 60
> degrees instead?
> 
> Or for the other case -- DIS module running a TBI
> ECM (i.e. a newer
> V6/60 engine's DIS module hooked to a 1228062 TBI
> ECM), couldn't this be
> handled by choosing how the plugs are wired?
> 
> Could the base timing value in the ECM be adjusted
> to compensate for
> either case?
> 
> The whole problem of when the ECM is triggered
> relative to spark event
> (base timing) seems pretty easy to overcome.
> 
> I understand that with DIS you can have much more
> advance because the
> physical constraints of the rotor/terminal
> relationship are removed, but
> that's a matter of tuning the tables to keep the
> spark timing in check,
> right? Don't command too much timing and it's not an
> issue.
> 
> Jay Vessels
> 1982 Chevrolet S-10 Sport, 2.8V6 TBI
> 1984 Chevrolet S-10 Blazer Sport, 2.8V6 (TBI
> pending)
> 
> 


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