I have a 98 Accord, 4cyl 2.3 with approximately 65,000 miles on it. The car seems to run great, and by great, I mean, it seems to not have lost any power over its years. I have noticed that during mid to upper acceleration, it will sometimes spark knock. I have not heard it during lower acceleration (0-40mph). An example would be on the highway if I go to pass a car, when I accelerate from say....55-65/70mph, I will hear spark knocking. As far as maintenance, the plugs have been replaced in the last year and a half. They were properly gapped before installation. I have not replaced the wires or distributor/cap. I purchased the fuel injector cleaner and have ran that through several full tanks of gas. It still seems to be doing it though, in the upper accel. Also, I have started running 93 octane with every fillup. Is this merely a honda thing? or possibly needs a tune-up ?