2.5 tdi

[ainarssems]

As asked by christhompson on another thread about TDI engine EGR and wastegate so that I do not derail the other thread. This is about AKE engine in A6 but should be similar for A8 and other engines

EGR-exhaust gas re-circulation, under certain circumstances it opens a valve between exhaust to in-take so that exhaust gasses make it to the intake to reduce NOx pollution. They do have carbon/soot build-up quite commonly which causes intermittent problem progressing to permanent of valve not closing properly and under boost part of air leaks to exhaust causing loss of power, smoke from exhaust and excessive fuel consumption. I am not sure if it is legal but You can blank off EGR valve and delete function from ECU. EGR function also causes soot build-up in intake pipes and manifolds reducing their diameter and therefor airflow and power so I would recommend taking them off and blasted to clean and restore airflow. Ours do work OK most of the time but sometimes it lacks of power and has smoke from exhaust under acceleration. The plan is to blank EGR off , delete it from ECU and have the intake pipe and manifolds cleaned by crushed nut shell blast next summer when I do cambelt change until then I will just disconnect vacuum hose from EGR and blank it off.

Wastegate is internal part of turbo on these engines and it opens up when boost pressure reach certain level to reroute exhaust gasses straight to exhaust not going through turbo and prevent overboosting, if it starts stucking it does not close properly and some of exhaust gasses always leak straight top exhaust causing reduced boost pressure, power at cost of fuel consumption.