I've been trying to get the lambda system working on my 1982 244 turbo. Right now, the frequency valve buzzes audibly with the oxygen sensor cold or disconnected. Once connected, it quiets down and the dwell drops to around 11 degrees. The O2 sensor reads steady at around .7 volts and does not fluctuate (tested with the o2 sensor still plugged in).

I've tried:
Testing all lambda system wiring per Bentley, checked good
Tested pressure differential switch, and thermal switch, checked good
Tested Freq. valve resistance, read 2.7 ohm, seems good
With O2 sensor disconnected, dwell reading is a normal 43 degrees
Replacing o2 sensor with a new one
Replacing Lambda computer with a junkyard unit

The only possible things I can see that might be wrong are a bad O2 sensor, or a bad computer, which seems unlikely since I've replaced both with to no effect.

I'm stumped.

Any ideas?

--
Eric, 1983 245 ti

A bit more information:
The lambda system was working earlier, but it stopped sometime after the wiring harness was replaced. Right now I am inclined to suspect that I may have inadvertently gounded the O2 sensor wire while putting in the wiring harness and killed the first sensor. The second one I just put in was contaminated with antisieze because the protective cap had fallen off. Would this prevent it from working? The mixture was not changed since the lambda system was working and I think it is running close to stoic with the sensor disconnected, although I do not have access to a CO analyzer.

Eric
--
Eric, 1983 245 ti

There have been some definitive discussions here concerning this. Try searching the archives using key words like mixture, dwell, smog, frequency, etc. You may only need to adjust the mixture. It seems unlikely the adjustment would have changed by itself. Has the lambda system ever worked? Perhaps a previous owner played with it in an "attempt to get more power".

My guess would be a bad frequency valve or CPR. Your lamda computer and O2 sensor sound like they are working. If your dwell is low the Lamda unit is trying to lean out the mixture. This corresponds with your O2 sensors rich reading. The frequency valve would buzz with the O2 sensor cold or unplugged because the Lamda unit would be working in open loop.
I would swap in another frequency valve first, and if that did not work I would test the control pressure from your CPR.