With only 10k miles on it, your muffler is most likely not the culprit!
A "muffler garage" mechanic and two Toyota repair estimators couldn't tell me why the muffler on my 1988 Toyota Camry (four cylinder) literally blew up! After driving about 20 miles in the mountains, I heard a pop. The muffler had bulged and split at the seam, creating a hole 12 inches long by one and a half inches wide. The muffler was just over a year old, driven 10,500 miles. The car has 54,500 miles on it and is serviced regularly. There were no holes and no rust on the muffler. No one can tell me what happened, or how I can prevent it from happening again. Can you guys?
RAY: Of course we can, Romair! Are we not America's foremost authorities on all things automotive?
TOM: OK, so Ann Landers has a slightly better understanding of sequential multi-port fuel injection. But we'll try to help you anyway.
RAY: We do have an idea about why your muffler blew up. My guess is that unburned gasoline got into the exhaust system, and that the intense heat in there (from driving in the mountains) ignited the gas and caused the explosion. And the reason your muffler exploded is because it is the "weakest link" in the exhaust system. It's the part with the weakest seams.
TOM: Why was unburned gasoline getting into your muffler? That's the question your mechanic has to answer, Romair. If one of your cylinders were not firing correctly, or if one of your injectors were putting in too much gasoline from time to time, unburned fuel could be passing through a cylinder and getting into the exhaust system. Normally, unburned gas that gets past the cylinders is burned in the catalytic converter. But maybe there was just too much of it for the converter to handle?
RAY: The problem is, replacing the muffler won't help. The explosion was caused by an engine problem. And unless you find and fix the problem, your next muffler may go "ka-blooey," too.
TOM: So it's time to investigate. Have your mechanic start with an emissions test. That should confirm the unburned gasoline theory, in which case you can look to the fuel injectors or to the secondary ignition system (to see if one of the cylinders is NOT getting adequate spark).
RAY: If the emissions test does not confirm the gasoline theory, then I'd have to suspect foul play in the explosion. Do you have one or more an ex-wives, Romair?