DIS for GMECM

[Shannen Durphey]

Oh, no no no.  DIS ignition signals output by the ecm are shaped and
timed differently than HEI or distributor type signals.  Distributors
use varying dwell, adjusted for rpm and battery voltage, where DIS
signal "dwell" portion is exactly 1/2 the duration of the "fire"
portion.  In addition, a GM DIS system's reference signal is quite a
bit advanced compared to the dizzy signals, as much as 80 degrees. 
This would mean the ecm commanded advance of 30 degrees would equate
to 110 degrees at the crankshaft!

If dizzy/DIS swap were easy, the SYTY guys would all be running sans
dizzy, and the GN guys would be running sans MAF sensor.

Shannen

mta228 wrote:
> 
> I am a bit confused on this one.  Why would you need a little box to set
> between the ECM and the DIS ignition module / coil pack?
>     I thought it was simply a matter of wiring the EST, BY-PASS, and
> Reference supplied for the old HEI distributor system into the corresponding
> terminals on the DIS ignition module.  Does the ECM somhow know that the
> ignition module has determined its reference pulse from a crank sensor
> rather than a pick-up coil in a distributor?
>
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