My 1996 with 3.9 runs real rough. I have replaced cap, rotor, plugs,o2 after the catand tps. The plug wires are fine, maybe a year old. For a while now it would run fine and every once in a while it would sputter and go back to running fine. Sounds like a popcorn popper in there. Now thats all it will do. It will idle ok, gets rough then idles ok but when you step on the gas it just pops popcorn. Sometimes it will spit out a poof of black smoke from the exhaust when it pops. Has no power at all, it almost didn't make it up the ramps to change the o2. I was told by a friend it might be the cat but I want to rule everything out before I go doing that. Any suggestions would be a great help.
Thank you

 

it us reall easy to check the cat, just disconect the Y pipe and start it up. if the engine runs fine (will be loud as heck!) then change the CAT. Have you put a timing light on it to see if your dist or timing chaine might be bad?

 

I changed the coil today, no help. I haven't checked the timing because it has been going through these spells for about a year, funs fine, the sputters/pops for a little bit the back to fine, now it's not even got enough ***** to drive up the ramps in my driveway. I have been trying not to cut the weld on the cat, I can unbolt it from the manifold....

 

Yes you can unbolt it from the manifolds. Just dont drive around like that. This is a short test to see if the cat is cloged.

 

unbolted downpipes from manifold, did not help. Replaced all 6 injectors, did not help. Cleaned all the grounds on the engine, did not help. I'm starting to think t6he only thing that will help is explosives.

 

Does your truck have a cam sensor? I dont have a manual for your truck... If your cam sensor is not working correctly it might cause this issue.