[phonefixer]

I recently began hearing a tapping when starting my 1998 silverado, it doesn't matter if the engine is warm or cold. it goes away after a while. i am pretty sure that it is a lifter losing prime, but not positive. i just noticed my water pump is leaking. it has about 70k miles on it. the truck has 173k miles. it has been good to me. i have never been into the engine before. i am trying to make it last one more year. the intake manifold has been leaking for a year or so, just enough to tick you off. i was thinking of replacing all of it at once. here are my questions--
should i replace all of the lifters or only those that are either sticking or losing prime?
do i have to remove the intake to replace the lifters? (if so i will fix that gasket at the same time)
if the lifter(s) are bad, is this a sign of more problems sooner than a year from now?
is there anything else you would do while you had the engine partially disassembled? what about timing chain while the water pump is off and out of the way?
is there anyway to safely clean carbon from the engine. i have heard of running deisel through it for a little while and then replacing the oil. i plan on replacing my hoses, belt, valve cover gaskets, and thermostat. i put plugs, plugwires, distr cap, and rotor button on about 30k miles ago. what about cleaning injectors, i am not completely sure how this works.
i know this is a lot of questions...any help would be appreciated.
thanks