First time poster here. Here is whats going on, its a 2000 super duty. went two tracking yesterday because i finally got my new nitto mud grapplers and had to try them out. We went through some mud then drove home (running fine) a couple hours later we went to town (15 miles or so) ran fine there then part way back started missing when i let out the clutch as soon as it came under load. then started missing bad. low rpms the more throttle the worse it gets. high rpms its barley noticable. My first thought was she sucked in some water so i drove it home and parked it. Got home from worked today and fired it up and took it for a drive same problem but now i smell sulpher rotten egg smell really bad so i figure its a cat so i check the temp of the cat and my temp gun maxes out at 900 and it maxed out so i figured my cat was plugged. Funny thing is i have a magnaflow cat on the way so i just cut mine off for now and it doesnt looked clogged or anything. i can see light if i look through it. took it for a drive with just my slowmaster in place and it seemed better but still no power and a slight miss. it is also idleing lower than normal by about 2 or 300 but it doesnt sound to bad at idle beside a couple misses every now and then. There is no smoke coming from exhaust at all and it starts fine. maybe a hint of blue smoke on a cold morning for about a minute. also no check engine light. There is no knocking or ticking besides 2 exhaust leaks. Im sure this has been played out a hundred times but can anyone offer me any help?

thanks alot

 

Also the truck has 290k soooo that could be a problem but it had plenty of power before yesterday

 

You probably got your coil-on-plugs wet. I'd probably look at changing the plugs and coils, they don't last forever.

 

Yup, the egg smell is because it's misfiring. When a misfire occurs, the unburned fuel and air mixture is pumped by the exhaust stoke into the catalyst, where it washes over the advanced coating on the catalyst honeycomb. The next blast of hot gas then ignites the mixture, driving up the catalyst temperature by as much as 800ēC and causing a marked deterioration in the catalyst, so that severe catalyst damage can occur very quickly. So yea, - THAT is what your smelling.