Audi A4 TDI B6 intermittent reluctant starter


New member
Oct 20, 2021
United Kingdom
Audi A4
Hello, a tricky one, I think:
Car is an Audi A4 TDI B6 130BHP saloon, 6-speed manual gearbox, at just under 250k miles.
Normally, starting is a breeze, a few short moments of cranking then we're away.
This year, on 3 occasions several weeks apart the following happens:
1. the car appears to start as usual then dies straight away;
2. first and second times I looked for error codes using a couple of basic devices - none found;
3. after, say, about 6 seconds of cranking there is behaviour like one cylinder firing (i.e. a regular power stroke - might be more than one cylinder - but not enough to run even roughly);
4. after another period of about 6 seconds of cranking more life appears and before long the engine is running normally.
5. first 2 times there was no smoke or smell of fuel, 3rd time did generate some white smoke (the getting going behaviour was slightly different, taking a bit longer)

After that all seems normal. There are no faults to be found, the fuel filter was replaced not too long ago. High revs are all fine. The fuel tank sender gives a correct reading so suspect nothing with the wiring to the fuel pump.

Is it possible for the fuel line(s) to somehow empty out after switch off (the only plausible explanation that my limited experience suggests). Or is there a component that, if it were not working, would cause these symptoms yet record no fault in the ECU?

Thank you in advance