Here read this post.
http://forums.tdiclub.com/showthread.php?t=208490
NutsandBolts wrote:
Injection start control is never good. It indicates that internally, the pump cannot correctly time the start of injection. If you want to condemn the pump last, then there are a couple of things to check:
-Make sure that the connector to the needle lift sensor on the #3 injector is tight, and that the wire appears to be in good shape. The injection pump determines when the start of injection actually happens by watching that injector, then adjusting the timing ring accordingly.
-Make sure that the bolts holding the pulley onto the injection pump are tight, and do no appear to have moved. This one is a long shot, but it's possible that the timing (when checked in relation to the crank) is jumping around a little, and the pump can't compensate fast enough.
Otherwise, I would say that the timing ring is sticking a little, and the only way to correct it without getting into the pump is to try running some Lube-Moly Diesel Purge through the pump (just pull the fuel supply and return lines off of the filter and put them in a jar of the diesel purge, then run it until the stuff is gone). I've had amazing results with that stuff, and the pump may just need a little TLC. If that doesn't work, then I'd say that an 11mm upgrade is in your future...
-Rich
Edit: The soleniod on the bottom of the pump controls the timing ring- I suppose that it's possible that the finger that engages the ring is worn, which could make the ring float around a little bit. That would also screw up the start of injection timing. How brave to you feel? You could take the solenoid out and have a look-see, but I don't recommend taking anything on the pump apart with it in the car. I'd rather have it on the bench to catch any parts that roll out (I had it happen on a 6.2l pump- won't do that again! Bench only for me.)
