My mother's car, a 1991 Civic Wagon, is pinging. I took out the Bosch Platinum plugs and put in NGKs, no difference. I fed it about a gallon of water through a vacuum line and made lots of steam, still no difference. I checked the timing and it was retarded according to the light, but the distributor is fully advanced. So I checked the cam timing (it was correct) and changed the belt, which was loose. No change yet. I have backed off the distributor to stop the pinging, but I would like to have the timing where is should be. Two things possibly related: a crank angle sensor and 02 sensor code (have not come back since I reset the ECU). And at WOT it doesn't usually go past 6000 rpm (redline 6500), it just slows down and stays at 6k (smoothly, no bucking, sputtering, etc.) unless I back off the throttle a little.

Any ideas? Can timing lights be wrong? Am I missing something?