Here's a teaser. My '80 Capri 2.3 pings only at cruising speed (light throttle.) I thought I had found the problem tonight, when I found that a previous owner had disconnected the manifold vacuum from the distributor advance. No manifold vacuum at a point where it should be high, so even the weak ported vacuum at that spot can advance the timing too much.
I hooked the manifold vacuum back up, and the car does run better, but the pinging is still there. Push the pedal down and it goes away. I did have the head off several months ago, and there was little, if any carbon buildup.
Any ideas?