obviously...any dead miss could be an injector or an internal engine problem (piston rings/cylinder walls)..
typical symptoms of high mileage (7.3L) injectors are...
hard to start when cold
runs like crap (or very reduced power) when cold (may run better/fine when warm)
if you can have a buzz test performed, LISTEN to the sound of each injector buzzing...any injectors that sound weak, or muffled during the buzz test are caused by normal wear at the poppet valve...as the injector (poppet) wears...it moves further and further away from the solenoid, which can delay the movement of the poppet.
since the inj poppet moves further from the solenoid...this will cause a mechanical delay in the time between when the inj receives the signal from the IDM and when the fuel is actually injected...ie..retarded inj timing.
On almost any vehicle...retarding the inj timing will result in poor fuel economy and less performance.
keep in mind that one bad tank of fuel (gas, water, poor filtration, low fuel pressure, etc) can wreak havoc on the plunger and barrel assemblies...and can result in a misfire or skip from the engine...
we see poppet valve wear cause issues (poor cold starts, lack of perf) on injectors in the 200k mile range...some go more, some go less.
Poor engine (piston ring sealing) condition can increase the poppet valve wear since the engine oil is picking up carbon (soot) from the combustion process...
carbon is pretty hard stuff last I checked...so excessive soot in the oil will cause increase wear at the poppet valve..causing the valve to move further away from the solenoid...delaying injection, etc.
