19 --- General causes
Carbon build-up in combustion chamber. After high mileage's have been covered a large accumulation of carbon may occur. This may glow red hot and cause premature ignition of the fuel/air mixture, in advance of normal firing by the spark plug. Cylinder head removal will be required to allow inspection and cleaning.
Fuel incorrect. A low grade fuel, or one of poor quality may result in compression induced detonation of the fuel resulting in knocking and pinking noises. Old fuel can cause similar problems. A too highly leaded fuel will reduce detonation but will accelerate deposit formation in the combustion chamber and may lead to early pre-ignition as described in item 1. Refer to fuel recommendation given in Chapter 5 - Fuel & Oil.
Spark plug heat range incorrect. Uncontrolled pre-ignition
can result from the use of a spark plug the heat range of which is too hot.
Weak mixture. Overheating of the engine due to a weak mixture can result in pre-ignition occurring where it would not occur when engine temperature was within normal limits.
© March 2015