X2 on what woodboat3 said.

Also if you replaced the Nozzles with Bosio Nozzles people say they make more noise.

An Air leak can cause the Nailing noise.

I do not know what the top of your Pistons look like but if there is any sort of a recess that the Fuel pooled in you could have had some Hydraulic lock going on. Unless before you installed the Injectors you cranked the Engine and blew it out.

As you said a higher opening/pop pressure would make the timing later/retarded and if that was added to other conditions that would make the Fuel Injection Pump Timing late you may need to retime the Fuel Injection Pump.

When step on it is the Power ok?

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84 300D, 82 Volvo 244Gl Diesel