injector pump is what mechanics call pump,
injectors are also called, nozzles, atomisers etc etc.
they are first tested in a lab setup - all 4 injectors should pop at equal pressure (I think 120 bar for 2C) - maximum variance allowed is 1 bar.
the pump should deliver equal quantity of fuel to all 4 delivery valves - the pump is a precision device and needs to handled and worked on like a surgeon operates on brain. Using hathora technique without using brains, not using factory procedure will render a garbage pump.
Once the lab has setup everything correct, the pump is installed on engine and timed with a dial gauge in relation to the engine - this way the pump can deliver the fuel at the exact right amount of time (pump timing)
This adjustment of pump timing is very very very miniscule and cannot be seen or tested by human hand/feel/noise etc. You need a dialgauge.
Once the engine is timed right, the piston rings expand under load at the right time, which results in less blow and more solid power from the cylinders. - I made a thread a long time ago about this, and later on other people have also made threads on rebuilding pump and nozzles etc.
