I have a Euro 1985 280SL. I think my frequency valve may be dead. It is not buzzing at all. I have tested my controller as outlined in the Probst book, and it appears to be working. The only time I can get anything out of the frequency valve is when I ground out the oxygen sensor lead as the book says to do. Then I get a duty cycle in the 90% range, and it will start to buzz. Otherwise nothing.

Any suggestions?

Thanks in advance.

Anyone? I have done a search, but can't seem to narrow the problem down.

Well, I finally figured it out after spending the better part of a Saturday. I got frustrated and started unwrapping wires that belong to the Lambda control unit, and behold, the ground wire had been disconnected and taped up under an a/c hose. Sure didn't look like it until I pulled it off. Don't know why I was getting proper signals from the unit when I ran the tests on it. Put the ground back on, and it works now. The relay on the add-on control unit was sticky, so I hit it with some contact cleaner after popping the cover off, and now all is well.