Martyn 2006 Q7 TDI

Audi Q7 start issue observations:

Preliminary info: 2006 Q7 TDI 3.0, 130000 kms
New battery, good cranking, good charge rate from ammeter
Leaving on trickle charge overnight produces same results – assume battery good
Jump start assisted produces same result – rule out battery supply
Oil changed for half of tests – no change
Air filter cleaned after half tests – no change
Fuel cleaner added for half of tests – possible slight improvement

First starts of day:
Exceed 10-15 seconds of cranking (in one go fully automated, or in several manually controlled cycles) Tendancy to do better with three manually controlled cycles of 4-5 seconds.
Crank speed increases very slightly after first 2-3 seconds then constant (oil getting in, starter seems ok)
On starting, smooth idle, pure white smoke (Getting some fuel prior to eventual firing)

Other starts:
Second start at 50 deg after zero to … min rest – strong
Third and subsequent – good, sometimes slightly laboured or 2 second crank time
70 ish degree warm starts – mostly strong
90 degree starts – mostly strong

4 observed ‘no start high resistance’ (doesn’t complete a crank) at all temp ranges and time after shutdown between zero and 30 min. (fuel in cylinders? / starter ?)
3 observed ‘no start’ high resistance’ after 3 long runs with heat soaked engine within 0-2 min of shutdown.
No clear trend – other than has occurred mostly for an attempt 0-5 min after previous running. Ie never after a long rest period.

Possible diagnosis ?
Battery power supply good
Starter appears good – supported by multiple strong starts when warm ? All starts are occurring at 100 RMP – what is the limits / standard ?
Glow plugs – lights go out, and nil codes, shouldn’t be a player at operating temp anyway.
Fuel pump supply – getting some fuel for start (white smoke), good strong running for remainder of conditions.

Fuel pressure ….
I suspect 10 Bar (PSI?) check valve at the common rail remaining open … could explain cold start issue because it is getting drizzle of fuel, and longer crank times whilst fuel pump gets rail back up to pressure. Hot start high resistance issue 0 to 5 min after possibly due fuel continuing to pool in cylinder - giving compression lock or pre-detonation. Second start immediately following this have always been ok - as that fuel would be exhausted through valve or burnt. Occasionally observe small bubble in clear hose (any significance ?).

Any takers ? seen it before ? I've trawled the forums.... none describe quite the same symptoms. Much appreciated for input before I go throw $$$ at Audi.