CIS Computer

[mcinturff]

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.

[psalt]

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.

[Nickshu]

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.

[T77911S]

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