[Gmecm] C3 mystery? Not so mysterious!

[David Allen]

> Neat car, Mr. Allen

Thanks!


> As you know, the 1226869 ecm is very popular with the Fiero crowd.
> Ludis Langens, once a major contributor to this list, was into Fieros
> once upon a time.

Thanks for the info! I remember Ludis's page from a while back.  Will look
it up again.  I do have duty-cycle measurement tools because some of my
microcontroller programs use PWM outputs. Plus the machines I work on for my
job use servohydraulics that are almost always PWM dyty-cycle controlled.
And yes, a test light will respond to a 12V PWM duty cycle but it will not
light up at very low duty cycles.  For that you need an LED light.

> There are posts in the "old" archives discussing wastegate coding in
> this ECM.  There are some valid rumors that the Fiero code is probably
> a precursor to the C3 controlled, 1.8 powered Turbo Sunbird, maybe 1986
> or 87 vintage.

  Interesting! I choose the 6869 because it was almost pin-compatible with
the original MAF-based ECM in my car. (and I wanted speed-density).  The
wastegate control functionaliy will be a nice bonus if I can get it working.
  As-is, with the wastegate at its factory 9 psi setting, the car is much
faster than I had expected. I'm afraid to push the engine any harder until
it is rebuilt.

> Ludis' page... someone here must remember that gem... has (gasp)
> schematics for the 1226869 which have pinouts based on (1) actual study
> of the ecm, and (2) the same boost friendly code found in the Fiero.
> Included in these schematics are callouts for pin A3, listed as Gate,
> and C7, Waste.  Possibly one or both of these pins isn't populated in
> your harness?  If you followed the wiring diagram for a stock 85 Fiero,
> they shouldn't be.  Possibly one of these pins might be the wastegate
> output?

Yep.  I got the stock diagram to do the ECM swap, and both these positions
are currently unpopulated.  After my trip next week I will do some digging
on this.

>
> You might want to use an oscilloscope to check.  A test light may not
> respond fast enough.  Then again, depending on the bulb in your light,
> lamp intensity may change with wastegate % duty cycle change.
>
> Don't forget to google "ludis langens page."
>
> Have fun.
> Zaphod