The only fire I've seen coming out of the exhaust on any of my cars was the time the soot in the Volvo caught fire after I fixed the turbo.
Apearantly there was quite a bit of coked oil and soot in there from turbo seal leaks and bad performance (the EGR would stick open at full throttle, made an immense amount of smoke), and after pulling a long grade, it burned. Chunks the size of my thumb blew out from Louisville to Evansville on downgrades that night, quite spectacluar. I had to replace the exhaust soon after that.
The old 50's trick of blowing flames out the back was performed by a spark plug at the tailpipe and pulling the choke on a hot engine and flooring the throttle. The excess fuel burned in the atmosphere as much as in the pipe.
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!