Volvo: 1983 240 FI relay, k jetronic, oxygen sensor

Question
Thank you for the prompt reply. In answer to your questions about the relay
replacement, they were replaced with new relays and the noise still exists when the poor running
condition exists. Would that likely be a problem with supply votage to the relay or a problem with
one of the devices to which the relay supplies voltage? The Oxygen Sensor has not be replaced
during my history with the car.  I will investigate that. Thanks TD-------------------------
Followup To
Question -
My 240 with K-Jetronic injection goes into a very poor running mode after running perfectly for
15 minutes or so. When this occurs a slight buzzing occurs at one of the two relays under the
passenger side dash. The relay is quite when the the car is running well which it does most of the
time. Both relays have been replaced with no change occurring. Where do I look for the problem?
Answer -
When you say both relays have been replaced with no change, does that mean the noise went
away, but the running problem remains, or that the noise didn't go away, and the problem didn't
either.  Did you replace the relays with used ones or new ones?  At first glance, it sounds like you
might have a bad or dying oxygen sensor.  When was the last time it was replaced?  They usually
need to be replaced every 30K miles.  Let me know.

Answer
The thing that throws me most is that the new relays are still buzzing.  I've not heard of that before, generally when they are new, and there is some other voltage problem, they are either on or off, without making audible noises.  It's possible there is something else under your dash that is making that noise that I can't think of right now.  Meanwhile, besides the oxygen sensor replacement, another thing to check is the frequency valve, below and to the front of the injection manifold.  It is SUPPOSED to make a buzzing when the engine is running, and helps control fuel timing.  If it dies, or malfunctions, it can cause your type of problem.  Who knows, it might even create that buzz under the dash when it fails (I haven't experienced a failed one myself, so I'm not sure).  Anyway, check that valve out as well, it might have an issue.  Another thing to check is the knock sensor on the distributor as well as the distributor itself.  A failed knock sensor can again cause non-fuel related but equally frusturating symtoms like you describe.  Good luck!