I have a Volkswagen Golf MK4 1.9TDI, and I recently had that fault pop on my diagnose.
17656 - start of injection regulation.
I was told it was from the timing setting on the injection pump, and I decided to give it a check with the TDI TIMING and it showed up as 255+, which should be between 40-60 as the graph shows. I turned my 22mm bolt and tried to align it and I managed to get it done and got the timing down to 55. When I tried to start my car the next day, it just started cranking, but didn't start. I then turned back the same bolt a little and then it started but the timing was back to 230-240 and the car started running poorly again. Why does my car can't start when I put the timing right?