A6 1.9 TDI Warm Start Judders!!

[mrcheeezy]

My 2003 A6 1.9 TDI has started to give me problems starting when warm. It starts fine when cold runs fine and pulls great but when warm it sometimes fails to 'catch' first time and judders quite violently. After 3 or 4 attempts and keeping it turned over it will eventually start but it doesn’t sound good - it gives a loud 'knocking' as if misfiring. it doesn’t do it all the time and I think it must be fuel related. Any clues anyone before I go down that very expensive dealer path.

Thanks

Paul

[a8 tech]

Possible conflict of temperature readings between coolant sender and fuel temp sender and air temperature.Most likely coolant but you may need to post some fault codes if any or if possible.Does it also black smoke when hot start issue occurs.Regards Jon

[mrcheeezy]

Thanks for responding.

No fault codes and no black smoke - temp gauge looks ok too. Does the ECU/management system have a different temp sensor? It starts fine once cooled down a bit.

Could it be dirty injectors - which cleaner additive is best?

[a8 tech]

The coolant sender has 4 pins.Two for the dash display and two for the engine control unit.Try to get a reading from the sender when warm start occurs to see if the reading is accurate anf that it doesnt jump about to much.The sender will only register faults when the voltage is lost ie open circuit,short to posotive,short to earth.It wont on the earlier version register a fault for irratis or incorrect readind from the sender itself.

[mrcheeezy]

Thanks,

Got the sender off - not the most accessible position!! Anyway, when I removed the connection block it appeared to be full of oil around the terminals!!??? - I take it that this is not right - possible waterproofing???

Tested the terminals under cold and hot conditions.

One side gives 800 cold and 140 hot
the other gives 1800 cold and 300 hot (twice the other side) - should they read like for like at the same temperature?

Also I was expecting a Green connecter block (according to Audi) but mine is black with number 078919501c - is this the right one for the car?

[mrcheeezy]

Temp Sensor changed but still the same problem - it does not like warm starts at all!!

Could it be vapour locking anywhere?

[222637]

My 2003 A6 1.9 TDI (Multitronic) has a similar problem starting when warm. The engine judders quite violently but does not start for some time. Get worse the hotter the engine becomes. After a long drive it become even more difficult to start.. It starts fine when cold runs fine and pulls great. Starter motor is fine.

The local agents say that the flywheel needs to be replaced. Difficult to belive this.
Any clues on where the problem could be and how to solve the problem.


Appreciate and help on finding the fault.


Ravi

[mrcheeezy]

Mine is still doing it exactly as you describe. I cant belive its a flywheel issue i think it must be fuel related - still investigating.

[a8 tech]

Check the cranking speed of the engine and try to fast crank it with a battery booster to see if its crank amperage related.Also check for any fuel leaks around the fuelpipes or even replace the fue lfilter,try that lot first and let me know.

[222637]

Replaced the flywheel few weeks ago, and the problem was solved.

I understand there is a gel inside Audi TDI’s flywheel to provide some play to start the engine. When this gel gets wasted the play increases as the Engine get hotter and leads to warm start problems.

Ravi