What cause a pinging or tapping sound under the valve covers of a Cadillac Brougham?

engine ping

engine pinging can be caused by several different problems.here is a list of things to check.

low octane fule.use higher octane fule.

ignition parts .replace spark plugs,ignition wires,distributor cap andignition rotor.check ignition coil.

egr valve not working properly.check diaphragm and vacume line to egr.clean carbonbuild up in the intake manifold between the egr valve and throttle body.

engine running hotter then normal.check antifreeze,thermostat,electric fan,fan clutch.radiator and water pump.

engine timing out of adjustment.have timing corrected, checked for,worn timing belt or chain,worn out distributor shaft,timing adjustment on fly wheel.

===other ping or tap under the valve covers==

sticking lifters, excessive clearances, some parts loose inside the valve covers, pushrod(s) bent

A farmers' method is to take a long screwdriver, put the handle against your ear and the blade against valve cover with engine running (be careful so nothing you wear nor any body parts are caught in the fan and the belts, and that you don't burn yourself on the engine or exhaust headers) - by moving the screwdriver blade front to back on the cover, and even down to the block between exhaust ports, you should be able to hear where the noise is located.