In the workshop recently an Audi S7 V8 twin turbo customers complaint described as engine stalling and then difficult to start it was also mentioned that on starting an unusual noise was heard . The vehicle had been recovered to the workshop and initially after checking visually for any signs of issues alongside basic levels we started the car with no apparent issues . After allowing the engine to warm up at idle we then increased engine RPM it was then we heard an alarming noise which increased with engine speed but was also present on lifting off the throttle the noise appeared to be coming from the turbo area of the engine and a severe vibration could be felt on the n\s turbo . After consulting with the owner we stripped off the inlet pipe work to inspect the turbo’s . The n\s turbo bearing’s had failed completely and the compressor wheel was machining itself into the housing there was also wear in the o\s turbo .
We decided to see if there were any known technical bulletins relating to the failure and there was a known issue and the symptom’s matched the original customers description of stalling followed by poor starting . The turbo’s can be starved of oil when a small oil strainer where the turbo’s oil feed originates from becomes restricted and reduces the oil flow and results in turbo bearing failure . Having established the failure and cause we again consulted with the owner and he approved the repair which is quite substantial requiring putting the front of the car into service position , removing the turbo’s complete with manifolds , stripping out the centre cover to access the oil strainer and non return valve .
Turbo’s removed Old turbo’s
The oil strainer has been modified, with a new one fitted and a new non return valve we could start to rebuild .
Oil strainers old and modified and fitted into housing prior to reassembly
Two new turbo’s were installed along with all new oil feed and coolant pipes , all gaskets were renewed along with all new studs and fittings as required . A new genuine air filter installed and fresh engine oil and filter . The cooling system was vacuum filled with new genuine antifreeze and with the oil system primed we ran the engine up to temperature and after inspecting for leaks the final part was an extended road test to confirm correct operation and boost .
The vehicle was restored to normal operation with normal starting idle and turbo boost .