I wonder if anyone can explain why my 2003 CLK 270 CDI won't start since I have removed one injector to replace the leaking copper washer. I think this is a fuel problem just because I can't think of another explanation. I know these engines can need quite a lot of cranking to get the fuel pressure up when the fuel lines have been opened. I have changed the filter before and I remember it took quite a while to get the engine started. Prior to the injector removal it started and ran fine. I had just taken it for an MOT after having put some Wurth additive in the tank to get the emmissions down. Can anyone tell me: Do the solenoids on the injectors only open if the sensor on the common rail senses high enough pressure? If one solenoid does not operate does that stop the engine starting? The resistance of the solenoids (the two I measured are 0.3 and 0.5 ohms) I assume that is normal? There is another injector leaking that also needs the seal replacing but I planned to do one and see how it went prior to doing the next one. I know I have diesel in the common rail and the pump can pump it to the injectors. What I don't know is whether the pressure is high enough. I am wondering if the pump is worn and was able to maintain the pressure before doing the work but cannot build enough to raise it passed the sensor threshold. It seems unlikely this would be the case but I can't think of another explanation. I have tried cranking the engine over and over and I have primed the pump with a hand primer. As far as I can see the air is out of the system. I can use the hand primer to push fuel through the high pressure pump and the common rail into the injector pipe so expelling the air. There is no firing at all which I think is to be expected if the pressure sensor in the rail is not seeing high enough pressure. I appreciate anyones advice before I begin removing the lift pump and getting it tested.