I have had this chronic ping on my 1980 245 for quite some time, and it is driving me crazy. I've tried higher octane fuel, replaced the oxygen sensor, and had the timing in about every position possible (currently at about 6-7 degrees). The ping is obviously bad under acceleration, but it's also bad just sitting and idling, so much so that you can clearly hear the clicking inside the car. Under the hood, I can hear the click most prominently under the valve cover right at cylinder 4. Could I have a bigger problem than normal knock a lot of people struggle with on this board? I haven't really noticed a loss in power or diminished fuel economy, and the head was remachined and a new head gasket put on a year ago. I can't seem to find any other problems with the car, save this blasted pinging. What else can I do to help fix or diagnose this problem? Thanks!

Jason