My 2005 Nissan 4cyl manual Frontier pings ( spark knock) at low gear. The dealership in Spartanburg, SC said timing is done at the factory and cannot be adjusted at the dealershoip. Their adviceis that the only thing I can do is use Shell Premium gas. Itried this but it still pings. Someone on line said I need to replace a PCV filter, which I can't even locate.I used Berryman B12, Lucas Oil Upper but it still pings. How much is this damaging the engine? Are there spark plugs on this car, so I can replace them right now? read full review »