Ive got a 99 f150 w/ 4.2. It has always ran fine w/o any problems. The driver side header had been cracked for some time w/o any problems but a ticking noise. Finally I got around to changing it. One of the studs was broken off so it had to be drilled/tapped to 10mm. I changed it out and afterwards the truck ran HORRIBLE sputtering, feeling like it wanted to die out, making a popping sound, and wouldnt go over 25-30 mph being floored in which it would just sputter and pop as it ran. A 1.5 mile drive made the cat glowing red. Thinking the cat maybe have been plugged I changed both cats out and still got the problem. Today I pulled the head off to see if the drilling may have messed it up and that doesnt appear to be the case. The plugs were changed as well. Does anyone have some sort of idea as to what could be wrong?

 

Usually a glowing cat is caused from too much fuel being delivered to system, check for a failing fuel pressure regulator or else it is a failing coil pack? Have you checked the service engine code yet?

 

Did you by chance get the plug wires back on wrong? That would explain the glowing cat and rough running/no power problem.