Bottom engine knocking sound

How many miles on engine? Was oil changed after it ran hot? Install a good mechanical oil pressure gauge to see what is really going on. Also might use length of hose put one end in ear and listen with other end to locate exactly where noise is coming from. BE CAREFUL NOT TO STICK HOSE INTO SPINNING PARTS. If noise is from bottom of engine bearings may be shot. However, it could be mechanic left some part loose and that would be an easy fix.

I currently own a 2003 isuzu rodeo that i purchased new in 2003 i recently changed the oil and was driving and heard a loud knocking / banging noise . I immediately pulled over and shut it off ,popped the hood and checked the oil only to find out i had plenty of oil. i asked a mechanic he told me to replace the oil pump and i did , but it still makes the same noise. it only has 80,000 miles what else could be wrong?

Oil pump pickup screen may be clogged (in oil pan) from lack of use causing sludge buildup.

Well,
There could be a few causes. The rap really could be the bottom end, or number 3 cylinder, or piston slap (when cold), a belt-driven component or cam drive components or even a nerfed valve. The best way to find out is to listen, but I illustrated the Timing Light Trick first if your ears aren't trained (and while you are hooking up that light with the engine running, take the time to listen to it and 'train' your ears to finding out what the heck that noise REALLY could be and what it certainly ISN'T (such as a bubble in the tire thumping the fender, but hey, you are stopped with the car in park while you're hooking up that light, right? (Always work SAFELY).
Here's the breakdown before you declare it's the bottom end:
1) Connect a timing strobe in accordance with the manufacturer instructions to the main secondary coil wire. If you have a coil over plug installation, there may be an adapter you would need to get.
2) In idle, flash the strobe. If the knocking appears to be in time with the timing light, it's the upper half of the engine (cam, tappets, valves, etc.)
3) In idle, flash the strobe. If the knocking appears to be twice that of the strobe, you can conclude it's something in the lower half of the engine. Generally, crank journal main bearings make a worse metallic ringing under load. Connecting rod bearings usually quiet down under load if they're worn as the extra slack is taken up by cylinder pressure.
4) The most accurate test is to use your ears. Listen with a stethoscope all over the engine until you can tell me whether that knock is really a faulty power steering pump bearing, an alternator bearing, the number 3 cylinder or the camshaft. Take the time - you are training your ears to listen to what the engine is telling you.

Of course, if you have gas in the oil, it'll knock. If you did an engine flush, it may knock - all that gunk overloads the filter to the point the bypass opens in the oil pump - you're SOL if that happened. If you're out of oil, it WILL knock. If you changed heads recently and now you have a knock, the most likely cause for that is coolant in the oil; whoever changed the head burped the old one off without draining the coolant from the block. Even a small amount of it running down into the crankcase from that operation will create an acid that will destroy bearing surface material in a very short period of time. Even a complete oil change will not get all the contaminate out of the engine.
Lastly, Stop Leak may turn into Stop Engine - so if you use oil additives like these that can possibly clog the journal oil holes and cause a knock.

Bottom line - do your research, listen to what that mill is telling you, rule out belt driven accessories and oil levels (and condition) and when this knock started. Finally, tell me where that knock is coming from - a belt driven component, number 3 cylinder or the flexplate (auto slush boxes) or the flywheel (gearboxes).

The whining noise at start up is either the power steering pump (possibly low fluid, or faulty pump bearing), or possibly a belt on the engine. As for the knocking sound, that is hard to diagnose without actually hearing it, but based on the fact that you are hearing a whining sound at start up, which is indicative of a loose belt, I would start at the belt tensioner and make sure that it is applying the correct amount of pressure on the belts. If the belt tensioner is faulty, it can make a knocking sound. If that is not the issue, then it could simply be the lifters. With engine run time/miles on the engine, internal engine components, such as lifters, valves, bearings and any moving part, deteriorate from friction wear and heat.They have a tendency to make a knocking/rattling sound when they are building up pressure. When they build sufficient pressure, or the engine reaches operating temperature, this sound/noise will dissipate and become nonexistent. This can be remedied by changing the oil, and possibly the weight of the oil (5w30, 10w40, 20w50) depending on your driving habits , or conditions (Highway v/s City/Stop&Go, or short trips under 30 miles)

I hope that you have found this information to be useful, and if I can be of any further assistance, please let me know. Thank you for using fixya!

It sounds like valve train noise. The best thing to do is have the dealer listen to it and see what the preliminary diagnosis is of the nosie. Is the engine full of oil and it has been changed on a regular basis or at least every 5,000 miles.

The creek? Sure sounds like it. Have a mechanic listen to the knocking. Rod bearings or crank main bearings may have gone out.

No if the oil light has flickered you have oil pressure loss some time just belive the sensor do help us out. lifter do not cause oil pressure loss pressure is built in the rotation of the crankshaft. The knock under the plenum will point you to that cylinder that is affected, (main bearing) as for a 1995 the injectors can only cause a misfire but no knocking noise,will they honor the warranty

If your engine has a rod knock the engine has to be rebuilt or replaced rebuilt is about $2000 to $3000 dollars and a new motor even more.It is unusal for a rod to be out around 60,000 miles unless it was ran real hard or run out of oil or way low on oil.

Sounds like a connecting rod bearing problem. I would have a pro. listen to it.