Checking knocking

WARNING: This page is about a different car, the 2002 Volvo C70, 2001 Volvo C70, 2000 Volvo C70, 1999 Volvo C70, and 1998 Volvo C70. However, it is still accessible from the selected car via links, so may be relevant.

Abnormal knock may be due to any one of the following reasons (which are not listed in any particular fault-tracing order).

Oil contamination

If oil is sucked into the engine through the crankcase ventilation (due to a high oil level in the engine), combustion will be poor causing knocking.

Defective spark plugs/ignition cables

Can cause poor combustion causing knocking.

Defective distributor cap/rotor

Can cause poor combustion causing knocking.

Loose/defective knock sensors (KS)

Can transmit incorrect information about knocking to the engine control module (ECM).

Incorrect fuel

Can cause poor combustion causing knocking.

Extremely high engine coolant temperature (ECT)/intake air temperature (IAT)

Can cause poor combustion causing knocking.

Incorrectly adjusted camshafts

If the camshafts are not correctly set up the intake and exhaust times will be incorrect. Ignition advance will also be incorrect as the distributor is mounted at the rear of the camshaft. This can cause poor combustion causing knocking.

Mechanical knocking

Knocking may be due to worn mechanical components (for example excessive bearing play, excessive piston running clearance, valve rattle due to defective hydraulic lifters).