'97 205K (maybe a lot more). bought this truck almost 2 years ago. it had 157K but the odometer wasn't working. I got from a tow company, it had been parked for over a year. changed an injector, tuned it up, brake job and tires, she was good to go. Friday it back fired so bad it BLEW UP THE MUFFLER!!
Thought it was bad gas with the flooding. put in some seafoam, changed coil, cap, rotor, wires. it was good for about 20 minutes, backfired, and killed. it doesn't start up right away. brought it to mechanic shop, they found a loose pin in first plug on ecm. took it home last night on highway, it died. brought it back to shop today. it will idle without issues. when it kills it is faster than 35 mph. any ideas??? mechanics drove it around yesterday, no problems.
coding misfires
6cyl 5 spd MT

 

Cat plugged up is a possibility or a weak coil hows your spark pull a few plugs and look at them are they black and sooty?

 

no converter, brand new coil