[Gmecm] MAF specs and MAP replacement.

[Jay Vessels]

Hi there!

> starting to learn about microproccessors 

Ah, budding firmware engineer.  Pull up a seat.  Or, find a nice, fat 
connection and download (and read) the entire GMECM archives.  It's a 
great distraction from reality :)

> change the whole wireing harness but I would like to use MAP readings 
> and create false MAF readings on the output side of MAF.

The idea's simple enough but it's going to be difficult in practice. 
The MAF sends the ECM data in grams/second of airflow.  The ECM uses the 
airflow and a "load variable" which is calculated, to determine fueling. 
  Load determines target AFR (if memory serves) and airflow is used with 
the AFR to generate the injector pulse width.  It's not exactly like 
that in code but that's the idea.

However, you're getting load from the MAP sensor when what you really 
want is airflow.  Given the throttle aperture (TPS), MAP data, RPM, 
engine displacement, and VE, you can calculate airflow.

Of course, once you've calculated airflow like that, and you know engine 
load (TPS and MAP), you could calculate injector timing yourself and 
you've just built your own fuel injection controller.  To that end you 
might as well just use the right ECM for the job.

> primarily want to ditch the platinum and heat sink fins in the unit.   

Why?  MAF isn't a restriction in its measurement range.  If you need 
more than 255g/s then you need a bigger MAF and a different ECM (or 
pretty serious reprogramming) to make use of it.  New/reman MAFs are 
getting cheap, too, so cost can't be a factor.

> Anyone have any good idea about this.   I would love to eventually build 
> this device and sell it for around $100.

Neat thought but no market.  Who's going to buy it when for that same 
$100 (using the V8 TPI system as an example) I can convert to the 
1227730 ECM that is equipped to use MAP natively, and outputs a faster 
datastream?  V6 and 4-bangers have similar upgrade paths for similar money.

Your friendly firmware engineer,
Jay Vessels
1982 Chevrolet S-10 Sport, 2.8V6 TBI
1984 Chevrolet S-10 Blazer Sport, 2.8V6 carb. (for now)