[ischmitz]

Dennis, yes to all your questions. The S400 chip could be damaged. I've had several ECUs for repair where this chip was not functional. Sometimes it doesn't fail completely.

You can measure the current through the injector circuit by measuring the voltage drop across the 0.1 Ohm shunt. This is what the peak & hold driver evaluates for controlling the current during the hold phase. Compare the current pattern with a known good ECU. If you see differences then you found your issue.

I am not sure what the 300 circuit does. All 3.2 I dealt with didn't have this circuit. But my guess is that older versions used this as a linear regulator while newer versions use an integrated 7805 style voltage regulator. The +5V is the top reference for the AFM. If this voltage is not accurate you will have mixture errors.

Ingo