Half self start is not a tool to measure engine health, you might never know your glow plug system is rigged up with some "desi timer" which can mask a lot of problems. The original system does not even swtich on preglow when the engine is at normal temperature, at this moment the engine should take 2 to 4 revolutions of the starter to start.a very basic test of nozzle operation can be done with a stethescope, listen to all injectors - all should sound the same, if one is clangy or something then the injection pressure and timing is messed up for that cylinder, if your pump advance governor is not working you may have a very screamy and touchy engine but gutless under load. A stuck EGR can also cause the engine to breathe very heavy exhaust which in turn will cause very slow and black burn and have very low power output. Similarly a pump with low internal pressure can also do that.Lack of diesel engine power is mostly pointed out to choked out fuel filters - low fuel supply to diesel pump will cause extreme low power.