One the 3.9L V6 and 5.9L V8 the carbon buildup on the top of the piston is common. As the buildup increases with mileage and over time, symptoms may vary from light ticking, to ticking/hammering, to hammering/knocking noises. Fuel injector cleaner often solves the problem.

On 3.9L V6 and 5.9L V8 engines, the intake manifold gasket may leak and cause increased oil consumption and a spark knock during acceleration; the gasket should be replaced.