GM-GMC: pinging in 89 s10 engine, connecting rod bearing, valve lifter

Question
Hi i have an 89 chevy s10 and when u start it there is a loud knocking/pinging sound from the top of the engine,ive been told its sounds like a rod knockin,or a stuck lifter it will drive but it vibrates bad how can i know what it is an how do i go about replacing it,an can i do it myself i know a little about chevy engines but i need an experts advice, also i have a 92 chevy c20 van that when u turn the key off the engine wont stop for about 20 seconds after it just keeps rollin over...can u help

Answer
For the S-10, the noise and vibration you are describing could be either a valve lifter or a bearing knock.

A simple way to tell is to unplug one spark plug wire and then start the vehicle.  It will run roughly, and maybe even worse then it does now, but you will need to repeat the process for each cylinder.  When you get to the bad one, the engine will run as it does now.  If the noise goes away, it is likely a bearing problem.  If it does not, it is likely to be the valve lifter or maybe a bent pushrod.

Once you know which cylinder it is, you can remove the rocker arm cover and check that cylinder's rocker arms for looseness.  If you find a loose rocker arm, and the adjusting nut has not backed off (or even come completely off) check the pushrod and make sure that it is not bent.  If there are no indications of problems as I just described, you probably have a bad valve lifter but it is also possible that the lobe on the cam has rounded off.  The intake manifold will have to come off to allow removal of the valve lifter and inspection to ensure that the cam lobe is undamaged.

If it isn't in the valve train, you probably have a bearing problem in the identified cylinder.  That will require removal of the crankshaft from engine and that is a job best done with the engine removed from the vehicle.  All of the bearings should be checked for wear and replaced as required.  If it is a connecting rod bearing, or bearings, that assembly will need to be removed from the engine after removing the cylinder head.  The connecting rod will need to be checked for out of round condition.  This is major, and expensive, work.  It might be less costly to find another engine for the vehicle and replace it.

For the 1992 van, the engine has throttle body fuel injection.  For some reason, it is either not shutting off, or there is a leak in the throttle body assembly.  The vehicle has On-Board Diagnostics (OBD) and it should be checked for trouble codes that might help diagnose it.  Many auto parts stores will read the codes for free.  If there are no trouble codes stored in the computer, the throttle body assembly should be removed and checked for leaks.

Until the van is checked, and if it has an automatic transmission, leaving it in "Drive" while turning off the key may help stop the engine more quickly.  The shifter can then be moved to "Park" and the key removed.