we have a 4-53 diesel engine i am not much of a diesel person, but this thing has a miss/ low power it is in a log skidder, i was wondering how to test the injectors this is what the owner suspects.

since you question my advice here some explanation:
first of all, as a former chief engineer,I had lots of expierience with diesel engines and there related operating troubles, everything ranging from 10pk to 10000pk.everything between 100rpm and 1800rpm,2stroke,4stroke, different setups of turbo/blower charger,...
the detroits I have overhauled were V8 and V12 blocks
they were two strokes and charged with a roots blower.
the injectors were combined units (fuel pump and injector as a single component.Despite having worked so many hours on diesel engines,I can't say I know all ever manufactured diesels, therefore I looked for a picture.here are some typical values on component wear and there reflection
on engine performance:
injectors:wear on needles and seats,2000-4000hr,leaking injectors don't have to much impact on power output,improper combustion causes smoke and raised cylinder exhaust temperatures
fuel pumps:wear on helix and pump outlet ports,15000-25000hr,the helix on the plunjer and the outlet ports on the pump barrel defines the amount of fuel being injected.wear in the form of cavitation marks in this area causes the plunjer to seal off later, so the injection timing is retarded,this causes a drop in combustion pressure and decrease in engine power.
piston rings:they pass openings in the cylinder bore (air inlet ports) and sometimes brake.because its not a running time related failure, they need to be inspected on a regular base.since the OP mentioned the use of the diesel engine in a log skidder (I assume this is a machine to chop blocks of wood), before you hit the maintenance interval for pump plunjer/barrel (2 years continuous operation), you are a few years down the road.further,lack of power as a result of lack of compression is easier to detect without specialised equipment than as a result of fuel pump wear.(because of a bigger drop in engine performance)
see attachment for air box inspection covers

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