CIS Computer
 

Hey guys, I don't have the O2 sensor plugged in anymore on my '83 SC, my mechanic set up the CIS to run without it (yes, I know, it won't be perfect but it runs fine). Do I still need the computer under the passengers seat? I'm likely going to do an interior overhaul soon and would like to keep it minimalist.

Yes, if you remove the ECU the FV will stop pulsing and your fuel mixture will be too lean. The FV still pulses at the default settings with a defective or disconnected O2 sensor. One of the reasons the SC is so long lived is proper fueling, disconnecting the sensor is choosing to shorten it.

You still need it. With the O2 sensor disconnected it pegs the frequency valve at a fixed duty cycle, 50-60% IIRC.

With the O2 disconnected (from what I understand) you do get a more stable idle in the presence of a leaky (vacuum) engine, but you are robbed of WOT performance/output.

Psalt is the expert here, I learned from him here on the forum, I used to have mine disconnected until I truly understood how the system works, now I have it reconnected and dialed in properly. Porsche made many modifications to this system to optomize performance over the standard Lambda K-jetronic that was installed on VW's and Audis of the day. It was not simply a K-jetronic with the Lambda as an add on, it was much more integrated into the system than most people think. This includes the addition of a throttle position sensor that sends a signal to the Lambda brain to offer a richer mixture at certain throttle positions for higher performance at upper RPM's above the level which emissions requirements tested at that time.

+1 with paul.
if it is to just save money on a new O2, you are better off getting a new one.