Injection Start: Timing & Optimization

Could the injection timing on my 2.5 TDI V6 (121,000 km) already be so far out of alignment after the first timing belt replacement that it's causing starting problems? If so, how could this happen? Is it due to stretching or slippage?

Hello, hello!
It sounds like what I'm experiencing (V6 TDI AFB, 100,000 km, a lot of biodiesel used). Similar problems: error code 550 'regulation difference injection start,' cold start problems, the engine management system goes into limp mode. I had it checked out at the workshop (cost: EUR 75). The diagnosis: faulty injection pump.

After seeing the measurement report, I have to believe them (I initially wanted to replace the timing belt, not the pump, but I've now decided against that).

'Das ist ein sehr interessantes Thema, und ich bin froh, dass wir darüber sprechen können. Ich denke, es ist wichtig, verschiedene Perspektiven zu berücksichtigen, um ein umfassendes Verständnis zu erlangen. Es gibt viele verschiedene Meinungen dazu, und es ist wichtig, offen für neue Ideen zu sein. Ich bin gespannt darauf, was wir alles herausfinden werden.'

ZITAT ENDE
VAS 5052 Self-Diagnosis Protocol.
...
08 Read measurement data block.
Ad group 0.
...
32 62 0 23 100 215 71 170 127 110
...
04 Default settings.
Display group 4, system in default settings.
Default setting.
830 revolutions per minute.
late
3.4° North, East of True.
100%

Default setting.
830 revolutions per minute.
early
5.6° v.OT
0%
'QUOTE END'

If I understand correctly, this means that with a 100% duty cycle for the input signal of the injection timing control valve, an injection timing of 3.4° before top dead center (BTDC) is achieved. And with 0% (maximum advance), the injection timing is 5.6° after top dead center (ATDC). And the latter would probably be too late...

A possible cause might be dirt on the injector control valve (causing it to jam or become blocked), or wear and tear (allowing diesel to leak past the valve instead of exerting pressure).

On the other hand, you were already scheduled to have the timing belt replaced (at 120,000 miles/km) anyway!!

Okay, I'll just have the belt replaced now, since the injection timing will be adjusted anyway. I'm not sure if it's been exposed to biodiesel, as I only bought the car with 103,000 km on the odometer. However, mine doesn't go into limp mode; instead, after it finally starts, it behaves quite normally. The only thing I've noticed is a temporary, slight lack of power. There's no noticeable hesitation or jerking.
Since I've repeatedly heard that poor starting performance can be related to incorrect injection timing, I wondered if this only occurs after a poorly executed replacement, or if it can also be caused by factors like stretching, slippage, or other influences.
Interestingly, the error memory didn't report anything, but the battery had been disconnected shortly before; however, I think that shouldn't matter much with a TDI, as everything should be stored.

I'm currently talking to my VW mechanic, and he suggests you check if the tensioner lever between the tensioner pulley and the hydraulic (oil) tensioner is securely fastened on your engine.
This could cause the timing belt to be too loose, and the fuel injection pump would not have a clearly defined injection start.