Cylinder 4 sits at the back of standard 4-cylinder engines or in the middle of V8 blocks. Detonation in cylinder 4 triggers a high-amplitude signal on the knock sensor. The computer reacts by retarding ignition timing specifically on that cylinder. If the engine continues to knock, it sets a permanent code. Worn spark plugs, a lean injector, or low fuel pressure can cause cylinder 4 to knock.
Mechanic Glossary
4 Above Knock Threshold
An engine diagnostic code indicating that the knock sensor has registered detonation levels in cylinder 4 that exceed limits.
Frequently Asked Questions
The engine computer detected pre-ignition knocking in cylinder 4 that exceeded the safe operating noise limit.
Low-octane fuel, carbon buildup on the piston, a failing spark plug, or a clogged fuel injector causing a lean condition.
Replace the spark plug and coil pack, run a high-quality fuel injector cleaner, or check for intake manifold vacuum leaks near cylinder 4.