Could use some help and advise on this one please. Car arrives trailing plumes of grey/white smoke from the exhaust and a residue of a clean, light viscous oil like substance from the tailpipe but performing well.questioned customer re contaminated fuel and water and oil consumption none of which gave significant pointers to the cause of problem ie not topped up with oil nor water and levels were ok. Feel and smell of fuel were fine.

No eml was illuminated but fault codes retrieved were 4175 exhaust gas temp sensor before particulate filter signal error 4cf3 exhaust gas back pressure sensor signal error 4226 lambda probe signal or value below threshold there were also 6 codes for glow plugs. Road testing cleared the smoking up for short periods of time and showed no problems with performance.the breather diaphragm was checked and okd.the pipe to the pressure sensor was removed and when the engine was run small amounts of black oil were emitted.

We are sure the problem lies with the emission of this light oily substance but are unsure how to test for a) overfueling b)oil bypassing or excessive oil from turbo wear. If overfuelling was an issue would the smoke be black and performance affected especially at idle. If oil contamination would the smoke be blue. Bav tech is not great on its live data likewise modis but not sure what correct readings should be with regard to pressures and injector quantities etc.

Any help gratefully recieved