A friend of my has a older Ford pickup(1971?) and they blew up two mufflers and had a heck of a time figuring out what was the problem. It had a new distributor installed and the mufflers blew after that. What they found was the condenser was bad. It was new with the new distributor and they changed the condenser and the problem went away. For the life of me I can't see how a bad condenser would do this but it cured his muffler problem.