Correction: The $2.50 MC9S08 with the analog to digital converter is 16 pins and not 14.  We may get it smaller later on if I can get a cheap programmer.

This chip does not have a pulse width modulator so we are going to do it using a timer.

How that works is as follows you load the timer with a number that will give the desired pulse width. You then set the output pin high. When the timer times out you set the pin low. You then wait until it is time to send out another pulse and do it all over again.

A simple way to wait is to feed  an oscillator into the reset pin of the chip running at a desired fixed frequency for triggering the injectors. It then takes in an analog voltage from the MAF and goes through the motions of setting the timer and so fourth to output the pulse width.

Things happen so fast, on the order of 20 million instructions per second, the inherent delays in doing this are minimal. With an oscillator with a 10 ms period (100 CPS) 200,000 computer instruction can take place if my arithmetic is correct. Max pulse width would be 8 ms.

What this also does is make the microcomputer software  crash proof as it is always starting from a reset condition for each pulse.

The chip requires only two capacitor. Less parts than a 555.

Paul Lamar