Detonation (Engine Knock)

WARNING: This page does not describe the selected car, but rather 13 other vehicles, including the 1998 BMW Z3, 1998 BMW M3, 1998 BMW M Roadster, 1998 BMW 740iL, and 1998 BMW 740i. However, it is still accessible from the selected car via links, so may be relevant.

Ignition timing too far advanced.
Blown head gasket.
Stuck thermostat (engine overheating).
Lean fuel mixture.
DME/Motronic control unit malfunction.
No coolant in radiator/engine (engine overheating).
Wrong octane fuel.