[Diy_efi] GM timing signals

[Bill USN-1]

All,
I have a question and hopefully a fairly simple one.

I play around with the GM TBI systems, mostly the 7747 and 8746.

I have used the 7747 on a lot of different motors to include 4 cylinders.
I run the whole system with the stock 8 pin EST module.

My latest conversion is using the 7747 ECM and the DIS system from the 2.2
cavalier. I am running the system on a 1275 A+ motor in an older Mini. I use
it to drive the SPI(TBI) Mini throttle body and single injector by just
tying the 2 injectors signal wires together Since the pulses are alternated
from one inj to the other anyway.. The ECM just thinks there's 2.

When I researched this project, it appeared on the surface that the required
timing signals and the wiring were all interchangeable. But obviously it was
not that simple. It seems that the ECM timing signal is opposite of what DIS
wants to see. When I start the motor it goes to full advance and stays
there. At present I simply have the bypass disconnected, removed code 42 and
set the base timing to 15?. This gives me a total advance of about 30? in
limp home so it is at least drivable.

Does anyone have any specs on the differences in the timing signal from the
7/8 pin to the DIS?

I have read a lot of the data on the GM and DIS posted on the Megasquirt
board but it didn't really specify anything.

I even tried to read the patents I could find but they seemed really
generic.

I'm hoping there's a simple solution like just inverting the signal with a
switching transistor.(I can hope)

Any help is appreciated.

Bill
USN-1