audi r8 part1.pdf
Engine Component Damage (UK TPI)(2029773/4)
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process. No other damage or signs of seizure marks are evident on the piston.
The reason for this type of material erosion is caused by extended time periods of knocking
combustion. Pressure waves are generated during the knocking which spread across the combustion
chamber and down to the first compression ring. At the reversal point of the pressure wave, small
parts of the material are removed through kinetic energy. The small parts of the eroded material could
potentially cause glow-ignition which accelerates the process.
4.1 Possible causes
Use of fuel with inadequate knock values – octane rating too low or fuel does not conform to
Diesel in the fuel which lowers the octane rating
Diesel fuel does not conform to EN590 standard
Excessive amounts of oil in the combustion chamber (worn piston rings etc)
Compression ratio too high (large carbon build up, incorrectly machined cylinder head)
Ignition timing too advanced
Mixture too lean which causes very high combustion temperatures (consider injectors/fuel
Intake air temperature too high – possible exhaust back pressure or poor ventilation of intake
5.0 Erosion and build-up of sulphur within the combustion chamber
The customer’s complaint could be ‘reduced power’ or ‘poor running’. When removing the cylinder
head or checking with a bore scope, a large amount or discolouration is noted and often sulphur build
up is evident.
5.1 Possible causes
Using fuel that does not conform to EN228 standard (Petrol)
Using fuel that does not conform to EN590 standard (Diesel)
Using fuel with high levels of ethanol/biomass blends
Using non-approved fuel additives
Always consult the owner’s manual for guidance about fuel additives and types of ethanol/biomass
blends suitable for use in the vehicle.