1972 Ford truck 3/4 ton. Engine Size : 390
Question: I have a1972 ford truck changed the points, condenser, coil and cap. When I step on the gas it starts jerking. Backfires and dies but it will start up OK. Help. Frustrated. When i step on the gas to go fast the above happens. Slow runs OK. When I hit the gas the problems start.
Answer: engine misfires on hard acceleration is usually caused by a problem in the ignition system. I would also suggest replacing the spark plugs and spark plug wires. Or you can spray down the spark plug wires with water while the engine is running to see if it starts to stumble. That would show a bad wire. Hard acceleration puts a heavy load on the ignition and that will cause it to break down. Hitting the gas and driving normal does not cause such a heavy load and will usually not make a bad spark plug or plug wire breakdown.
Being as old as your Ford truck is, you could also have an engine mechanical problem. You could have a worn camshaft lobe. This can cause backfiring through the intake manifold. You could have sticking valves in the cylinder head, a worn timing chain and/or tensioner, a broken valve spring or some other internal problems. But start with the basics and get the ignition system in perfect working order.