Audi TT Coupe - Crankcase gas recirculation - Keith S

A number of motoring forums seem to be catching on to problems with recirculation of crankcase gasses into the inlet manifold to be burnt as part of the combustion process.

It would seem the blowby gasses pick up oil vapour thus coating the various sensors, hoses etc.

This seems to be more of a problem with direct injection engines - like those on modern Audis. The lack of fuel vapour into the inlet manifold means that a lot of the oil deposits are not washed away.

It all beggars the question, why dont manufacturers build a filter into the system to catch the oil vapour?

It seems most older cars seem to eventually suffer from rough idling due to blocked sensors, stepper motors, gunged injectors. Engines with direct injection now seem to be suffering from excessive carbon buildup on the valves etc. Perhaps a return to the old days of a de-coke every few thousand miles.

Any thoughts?

Audi TT Coupe - Crankcase gas recirculation - injection doc

Closed cuircuit crankcase ventalation has been a problem for years. Steam or water vapour injection in the manifold would keep all the valves & manifold a lot cleaner .

You can buy an aresol cleaner now designed to wash inlet manifolds & EGR valves but the only way to really clean an EGR valve is to remove it.

I agree its carp the way the gases cause other problems but thats the way it is.

Vauxhall 10+ years ago had to design an extra vapour/oil trap to fit as a mod on vectra's to stop the clag from causing too many issues with the throttle body & idle control valve but they still clogged up!


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