Q: I have a 1970s-era Ford Ranchero with a 302 engine with a two-barrel carburetor, a C-4 transmission, and an open-type rear axle with 3.08 gears (I think). The only modifications are headers and a dual exhaust.
At about 50 miles-per-hour and above, the engine starts to break up. Acceleration up to 50 is okay—the problem occurs only when cruising. I put a new distributor in, then replaced the vacuum advance about a year later. That helped, but the problem is still there, and the distributor has a new cap, rotor, points, and condenser. I checked the hose to the vacuum advance, and it’s okay, too.
I am also having a problem with the harmonic damper. I have gone through at least seven on three different engines. I’ll be cruising along and then boom—the damper breaks. Any ideas?
A: Does this engine breakup happen after you have driven a short distance at highway speeds, then accelerate? If so, take a look at your fuel delivery system. It could be that your fuel pump isn’t delivering enough fuel (low GPH). You might want to install a fuel pressure gauge someplace where you can watch it while driving. You will be looking for any pressure drop or a rapid fluctuation in pressure.
Your damper problem sounds more serious. Unless you’ve had the incredible misfortune of installing seven defective dampers, we’d say you need to look at the engine’s bottom end. Oil clearances out of tolerance or a badly balanced engine can cause a damper to fatigue or break. Your 1973 302 requires a 28-ounce total imbalance, which means the damper and the flexplate/flywheel have to be matched. You may want to double-check those components.
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