I went through two mufflers now. It will start and run fine. After turning it off for ten minutes I go to restart it, BOOM! Any ideas why this would be happening? Is it possible for fuel to get into the exhaust? I haven't checked anything yet because it's wintertime.

I own a 1992 4 cylinder rear wheel drive b2200 extended can fuel injected.

 

Yes, there is unburned fuel getting into the exhaust and then there must be oxygen in the mix as well. Last there is a source of ignition: any hot parts will do, including a fresh push of exhaust gases.

Check for leaking injectors. Check the ignition parts. Check the exhaust system for leaks.
Normally the catalytic converter should burn off excess combustibles. Quite possibly your converter is no longer up to this task.