Tapping noise - oil pump?

That's possibly a sign that one of your main or big end bearings is failing, especially if the tapping noise varies with engine revs. One way to make more certain is to pull off and replace the plug wires one by one while the engine runs. If the noise disappears with one certain plug wire disconnected, then that cylinder big end bearing is falling apart. The next step would be to remove the sump pan and inspect the bottom end bearings one by one.
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Model year ?

The oil light comes on when oil pressure falls below 7 pounds of pressure. A tapping noise from the engine is an indication of poor oil flow/pressure supply. You may have an oil pump failure or if high mileage, excessive bearing clearances that can cause oil pressure problems.

blown or clogged oil pump. The tapping noise may be a bearing or lifter, I would not run it until problem is fixed, you could blow a piston rod out the side of your engine. check the oil pump to see if is operating. if not, replace.

Sounds like you might have starved the bearings of oil which in your words , you've got a knackered engine. Probably too late for a pump.

bottom end noise usualy the knock of death for most engines
tap noises are lifters knock is crank or rod bearings. driving will only spin a bearing or weld it to the crank
if the truck worth it...used engine from auto wrecker
or spend that money on new ride

If it is a 'squealing' noise it's probably the alternator/power steering drive belt. Before you turn on the engine in the morning, lightlt smear or spray some oil on the inside of the drive belt to lubricate it. If the squealing stops/disappears, then that's the fault ..

That squealing noise can be caused by an incorrectly tensioned belt, or a worn belt. Replacement is the only option.

The other frightening sounds can best be described as 'rattles' or 'tapping'. When a car stands overnight all the oil drains back into the sump (oil/pan).

There are two things (usually) that can be cause the rattle/tap:
1. Because the oil hasn't been pumped around the system, at start up worn big end bearings can rattle and tap on the crankshaft until the oil 'fills the gaps'. The tapping/rattling goes away as the engine warms and oil is pumped around the lubricating system.

A 'bottom end tapping' is a symptom of worn big ends (they are bearings at the bottom of the piston and fit around the crankshaft).

2. A rattle/tapping from the top of the engine can either be a worn camshaft or 'lazy tappets'. Again, when the engine warms and oil gets to the camshaft and tappets (also called 'hydraulic lifters) the noise will disappear.

If your car has this rattling/tapping noise - identify whether it is coming from just under the rocker box (ie the camshaft/tappets..) or the bottom end of the engine (big end bearings).

If the noise is coming from the top of the engine, try an oil change with a can of thick 'additive' included. A lazy tappet (lifter) isn't too much to worry about. A worn camshaft will affect the performance of the engine, though continue to do its job. An oil change with an additive included may help in quitening things down.

A bottom end tap/rattle (or 'knock') - the sooner that is sorted out the better.

Sounds like you didn't put the pushrods back in the proper locations. There are two different lengths in this engine and you may have one backwards

The light comes on when the oil pressure is too low, when the sending unit is bad, and, if you have too much oil in the engine and it whips the oil so much that the oil pump cannot pull the oil in since it is mainly bubbles

The knocking sound comes from a shortage of oil to he bearings, tapping comes from the valve train under the rocker cover (cylinder head).

Make sure you haven't lost any oil & that it isn't overfull and correct that if needed. Beyond what I've mentioned, you would be looking at the oil pump needing to be replaced or major engine repair if the bearings have spun or worn excessively.

good luck

check oil level first.then have a mechanic check the valve train for wear .may need lifters and or rocker arms,push rod tips worn?etc..give me a shout back.wish you the best.