Well hell, then cut the cats out, weld in a straight piece, and keep on truckin.

 

Went with option 3. Had the two in line cats after the single O2 sensor cut out (both were ruined) and had a new Walker universal cat welded in with a new pipe back to the muffler. Actually has a nicer rumble now (while I was under it I saw it already had an older Flowmaster muffler) and the heat issue seems to be resolved.

 

Glad it all worked out. One other thing to possibly consider is banging on the muffler to see if it rattles. Ive worked on several mustangs that had the cats come apart. Most of them had flowmasters on them and on a few the muffler had pieces on cat in it restricting the flow a little.

 

Good point, I'll check.

 

So I dug a little deeper and maybe found another reason for my combustion in my truck, while underneath I noticed that part of the wheel well liner had melted slightly, didn't seen right to me. Went up a little more and saw that my AC Evaporator housing was melted out on the bottom. Tracked a little more and found that the side of the evaporator against the heater resistor was covered in burned leaves, twigs, basically a mouse nest.

So I think now I might have arrived at the real culprit, the heater resistor (which I had been testing heat and AC within 20 minutes of when the fire occurred) ignited the brush, melted out the evaporator housing, and then ignited the fiberglass side of the insulation exposed at that point.

 

Probably was a mouse nest lol. Did you take off the smog pump too? What did you do w those lines that went to the old system?

 

Nah left all the emissions stuff intact. The universal converter had a connection for an air input and they hooked it up when they installed it.