My car is a 2008 Audi A3 2.0 TDI (engine code BKD) showing 100,000 miles on the clock. It is serviced and gets new oil, fuel and air filters regularly. Over the past year, it has developed a strange fault. It starts up first thing when hot or cold, regardless of the outside temperature, for a day or two, but after 3-4 days it behaves as if there isn’t diesel coming through the system. It will eventually start on the second or third try.
Apart from this, all systems are OK and there are no warning lights. Audi has tested it for hidden faults, too. Aside from this, the car runs like new, cold or hot. George Patelaros The engine in your Audi is the Pumpe Düse unit. The injection pressure is delivered by the injector itself, using the cam lobe to operate the injector and provide the pressure. The injection timing is still electronic and a wiring loom runs within the cam carrier housing to trigger the injectors.
One problem that is very common on this engine is for the loom that runs within the cam carrier housing to fracture. This will give an intermittent connection and can cause a problem such as you are experiencing. A replacement loom costs around £60, but when this problem occurs it does normally trigger a fault code.
Other common faults include the failure of the injector rubber seals and problems with the camshaft operating system. If either of these are present I would expect to see smoke when the vehicle started and/or a slight misfire. As you report neither of these problems, we can hopefully discard these possibilities.
This leaves the fuel pressure system. One possibility is that the fuel pump at the end of the camshaft (tandem pump) is draining when left for a period of time, meaning no fuel is initially supplied to the injectors.
With this in mind, I would examine the fuel pipes and connections on the fuel filter. Also inspect the fuel pipes between the fuel filter and pump. There is a non-return valve built into this pump, but it can fail over time. A cheaper alternative to replacing the tandem pump, which also supplies the vacuum to the braking system, is to fit a separate non-return valve in the system. VAG manufacture such a valve (part number 165201542B) and it costs around £18. Fitting one of these in the return feed from the tandem pump to the fuel filter should remedy the problem.
The one-way non-return valve.