Sharan TDI Warm start problem

[timshaw]

Hi

I wonder if anyone recognises this fault:

TDi 1896cc 110 BHP (AVG engine)

Starts perfectly when engine cold
When engine warm it takes 4 to 5 seconds cranking to start. It doesn't matter what you do to the throttle and it always starts after about the same length of cranking time.
When started it runs perfectly OK

It's starting to pull the battery down when you have a lot of stop/starts during the day ...

[simo911]

hi
poss coolant or fuel temp sensor reading wrong when hot. need to get it plugged in to vagcom/bosch diagnostic tester hth simon

[timshaw]

Yes - that was what I thought of too - it checks out OK and anyway it's usually the other way round (poor cold starts and easy warm starts) if the temp sensor is u/s

Interestingly however, the problem disappeared when a new battery was fitted!

My theory is that if the engine is cold the ECU takes appropriate action and engine starts easily even with slightly poor cold cranking speed of a slowly degrading battery.

If engine is warm ECU takes no immediate action and engine is not easily able to start. I'm guessing that after a set time of cranking, the ECU decides it needs to help out by changing some settings and the engine is then able to start despite the cranking speed being a bit poor.

That's my best guess anyway.