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

I have a 1954 Convertible with the 359 engine and the original aluminum head. I'm using Champion RJ8C spark plugs, which would seem to be the lineal descendants of the J8 listed in the shop manual. I use premium fuel. The pinging happens only when under load, never when revving in park or neutral. I can eliminate the pinging by retarding the distributor several degrees, but the idle is very unsteady, vacuum gauge fluctuates between 13-15 inches until the RPMs go over 600. I have disconnected and plugged the vacuum advance, that made no difference.

I'm wondering if a colder spark plug might help, but it looks like Champion doesn't make a colder plug. The only other plug they recommend is the RJ12YC; the 12 in the part number indicates that it is hotter than the RJ8C. If anyone has solved this problem, I'd appreciate knowing what the solution is. Thanks.

Does the pinging occur at highway speeds and climbing a hill? And if you back off the throttle a bit it will stop pinging?

Could you be running too lean?

Running lean due to carburetor issues or a vacuum leak could cause it. A low carburetor float level could cause lean out and pinging, as could a restricted fuel supply. A problem with the distributor vacuum or centrifugal advance mechanisms could cause it. A stuck manifold heat valve could contribute to it.

A problem with the water distributing tube, if present, could cause it.

Be sure the plug wires are in the correct firing order. The engine should idle and run smoothly even with the initial timing set a few degrees later than spec.

Vacuum leaks can occur at the intake manifold gaskets, carburetor gaskets, throttle shaft, vacuum booster pump, and anywhere in a vacuum windshield wiper system or any other vacuum device, including the vacuum advance or an automatic transmission vacuum modulator.

***Overheating or heavy carbon deposits can also cause pinging. In the case of carbon deposits, driving the car on the open road for a few dozen miles at 50 to 60 MPH will usually get rid of it. Avoid hard acceleration or driving with continuous pinging.

Stale gasoline can lay down heavy combustion chamber deposits in a hurry, and stale gasoline may have much lower octane than it did when fresh. Be sure your gasoline is fresh.