Iv been chasing this code for th last 2 weeks. I can't seem to figure it out. Changed the plugs and tested the wires, swapped for newer coils and changed intake gaskets. Showing mis fires on 1,6,8 cylinders. The light only comes on and blinks under light throttle, after kicking the converter out. I've pulled the drivers valve cover and springs look good, although the plugs show I have a little oil consumption in 3,5 cylinders as well as 4, and 6. Not much oil has been burned less than 1 quart in last 2500 miles.

Truck is an '01 rcsb 5.3 auto, picked it up around 1 month ago. (lownslo's old green truck)
mods are
comp 114ls1 cam with 918 springs and hardened pushrods
full exhuast with ory-so that rules out cats
k&n intake
built 4l60e with yank tt3000 stall
msd wires


When i picked the truck up it had a nasty 1-2shift that would knock your head on the back window, and being that the computer was locked(stupidest **** ever) i bought another ecu and had my tuner tune it with efi live. With the old tune it never did this until we tuned it, guessing the misfire tables on the topend were cutoff. We tried doing a crank relearn but it would not perform.

 

You answered your own question.

If there is NO actual misfire then the tune needs to be adjusted for it. If it actually does have a miss then you need to determine were the problem is mechanically and fix it.

 

Try changing coils

 

He already did. This happened after he swaped ECU's and got a new tune.