[CrewChief]

The CIS for early 80s functions about alike for all the Porsche cars. In other words your car CIS is functionaly identical to the CIS in the 924. I have the supplement at home for details when I get there. The same supplement covers both cars.

FWIW at the moment.

The O2 is only really involved when the car is at idle. The various microswitches tell it when idle is by throttle position. The rest of the time the sensor is not really in use. By all accounts, and my experience, the early systems were not very good and will at best 'hunt' when using the sensor output. The cars do run better without the sensor.

However, the lambda computer IS required to run the frequency valve at all times. The CIS distributor is setup to see the frquency valve modified pressure in the lower chamber(s) and will not run correctly with a non-functional frequency valve. No matter what you do; it's just too far off. There is a table which shows the duty cycle of the frquency valve at various operating conditions. Most of the time it is fixed at 50% (IIRC) with microswitches to create accleration enrichement for a cold engine and full throttle enrichement. The table conditions depend on engine temperature, sensor temperature and throttle positions.

If the frequency valve is completely dead the most likely cause is bad connections and wiring. A quick check to see if there is output to drive the frequency valve is to find the 3 prong round connector that is for testing the signal. The red and brown connections were to power the factory supplied tool. Dont' short them. The black wire is the signal. Use a dwell meter to check the square wave to the frequency valve. Since this is a test coming directly from the computer you will then know if the problem is at or after the computer.

The CIS really functions quite well and has plenty of capacity for the power developed. The only major limitation is that it will not tolerate hot cams to jack up the power.