why do you have an 02 sensor on a carbie??? is that some freakish california thing?

Ding ding! We have a winner!

I'm really not sure what all the ECU does on this truck, I think Josh probably understands it the best. I did find the pinout just now, and here is what's hooked up to it:
  • O2 Sensor
  • Temp switch 1
  • Temp switch 2
  • Vacuum switch 1
  • Charge light
  • Tach signal
  • Vacuum switch 2
  • Speed sensor
  • EBCV
  • EACV
  • CMH
  • Fuel cut solenoid valve
  • VSV

According to the FSM it actually has a way of adjusting the A/F mixture.

My Truck: 1987 XtraCab DLX 22R 4WD 5 Speed Manual
"Speed has never killed anyone. Suddenly becoming stationary, that's what gets you." -Jeremy Clarkson