Detonation Or Knocking

WARNING: This page does not describe the selected car, but rather 7 other vehicles, including the 2003 Mitsubishi Outlander, 2003 Mitsubishi Montero Sport, 2003 Mitsubishi Montero, 2003 Mitsubishi Lancer, and 2003 Mitsubishi Galant. However, it is still accessible from the selected car via links, so may be relevant.

Check spark plugs for correct heat range.
Check fuel quality/octane.
Check for fuel contamination.
Check for intake system air leaks.
Check the ignition timing.
Check for carbon build-up in cylinders.
Check if head or deck has been resurfaced.