Packard Forum Index » Post-War (1946-54)

Valve noise that comes and goes often indicates gummed lifters.
A miss under load is often a problem in the ignition system. It could be a dirty, worn, mis-adjusted, or otherwise defective spark plug, a plug cable that has leaking insulation, a problem with the distributor cap or rotor, a coil issue, low primary voltage, or some problem with the points. Spark plug cables can look good and still leak high voltage to ground. Ignition system parts need to be clean, inside and out, that includes the distributor cap and rotor, the coil, all plug wires, and the spark plugs both the firing end of the plug and the insulator where the plug wire attaches. Spark plug wires that have rubber boots at the plugs can deteriorate and allow a spark to jump form the boot to the plug body which will cause a miss. The more load the engine is seeing, the more voltage is required to fire the spark plugs. That's why a miss that shows up under load is very often related to some problem in the ignition system.

Engines that have the plug wires inside a metal tube or holder of any kind often have plug wire shorts to ground within the metal tubes or shields.

Radio resistance/ radio suppression type spark plugs and spark plug cables do not work well on older ignition systems not designed for them.