Q: I have a Ford truck with a 390 FE engine. I had the heads redone and installed a new cam and lifter set, true roller timing chain, valve springs, single plane Edelbrock intake, adjustable rocker arms, and headers. I use the truck to haul my 12 foot camper.

When I reach highway speeds and keep the rpm steady, I hear a sound like a chain or marbles inside a coffee can. When I let up on the gas, the sound goes away, and when I hammer the gas hard, it goes away. I drove 1,000 miles with this condition. Is it the cam walking and hitting the timing cover? Could it be the lifters or valve springs?

ford 390 fe engine from 1976 ford f-100

A: Your sound does not seem to be caused by a mechanical problem. If it was lifters or valve springs, the sound would be constant, not just when you’re cruising. The problem sounds more like pre-ignition. There are several ways to cure pre-ignition:

  • Run higher octane fuel. Premium gas rated at 92 or 94 octane is best for an engine with a compression ratio between 9.25 and 10.25:1. Using premium can be expensive, especially in vehicles that use a lot of fuel.
  • Run the engine on the rich side. You can do this by using larger jets in the carburetor, or by running a colder range spark plug than the one you are using now.
  • Try playing with ignition timing. Most engines like to run more timing than stock specs call for. If you run too much initial timing, you will get pre-ignition; too little and you lose performance. We recommend starting initial timing at 10 degrees BTDC and adjust from there.

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