1998 BMW Z3 High RPM misfire

High RPM mean load.

It misfires erratically when it comes under load or accelerates. The engine is obviously misfiring under load but does not do it all the time. The most likely causes here would be a defective ignition coil, bad plug wires or worn out or fouled spark plugs.
I do not know what you mean by"coil ok".

I would suspect the cam sensor.
it is the only one responsable for telling the computer wich cylinder is a top dead center and wich one is approching so the computer can energize the relay ,so the relay can energize the injector.
fuel volume test is good approach, it seem like the engine is starving.it start and runs rough.
Low fuel pressure creates a lean fuel condition that can cause lean misfire, hesitation, rough idle, hesitation and misfire on acceleration (high rpm)
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Have the injectors cleaned, walmart is the cheapest place so far I know.plug injectors causing bad spray pattern can cause misfire.
check fuel pump wiring for moisture.check the fuel filter and lines for obstructions and the operation of the fuel pressure regulator before you condemn the pump.

On european EFI systems, the OEMs recommend using a static pressure test with the engine and ignition off. This is done by bypassing the fuel pump relay and energizing the pump directly

Static Fuel Pressure Test
With the key on, engine off (or with the fuel pump energized), fuel pressure should come up quickly and hold steady at a fixed value, one once per second.

Thanks for feeding that back to us.