misfire p3000 after catalytic converter replace

[Magnacharged H2]

I just replaced a clogged catalytic converter drivers side on my 2003 H2. Now I,m getting a misfire code.
Truck runs good once underway , but at idle it runs rough, rpms drop and coolant temps start to rise.
I,m thinking it is vacuum related. Anyone else have this problem after replacing a cat ?

[HUMTECH]

You only replaced one side? Are the o2 sensors working properly? Sure the muffler is not restricted? If the cat was welded in did they get a good seal at the weld points? Too many variables to diagnose without more info. Try to get a scan tool on it that can monitor misfire counts and find out which cylinders are misfiring. Check your o2 data make sure you dont have a dead or lazy pre cat sensor. Doubt you have a vacuum leak as that would increase idle speed and set a lean code.

[HUMTECH]

Oh and im assuming you have it supercharged. Was the repair done at a dealer? Maybe they reprogrammed your pcm thinking the updates would help and wiped out you ecm tune for the charger...

[Magnacharged H2]

Thanks for the reply Humtech!
The scanner I have reads random misfire right bank , but not which cylinder it is.
I replaced the drivers side cat with a Magnaflow universal cat. I welded in myself.
No dealer flash on ECM .
I, ll see if I can get someone with a better tech tool to check o2 sensors
Thanks

[HUMTECH]

If your misfiring on the right side ill bet that cat is plugged as well. Anything over 0.5psi backpressure can cause misfires on that bank

[IRA51]

Over the years I have found that it's best to replace both cats and all 4 O2 sensors at the same time . Did you weld the cats in while they were on the vehicle with the battery conected ? If so ,your lucky you didn't fry the computer.

[HUMTECH]

As long as your ground is on the same pipe your welding it will be fine. Never ground on the other side if you have true dual exhaust as you could cause arcing across the piston rings to cylinder wall.

[Magnacharged H2]

No all welding was done off the truck.

I replaced the passengers side cat about 8months ago.

I started have the random misfire code after replacing the drivers side a few weeks ago.

I only had the code for a bad cat on the drivers side then after replacing It started with the random misfire code.

Is there a way to test the individual coils ? Maybe with an ohm meter ? what would be the number range I,m looking for.
Thanks

[HUMTECH]

Does it seem worse when cold? Could be intake manifold gaskets leaking. they have updated design gaskets for the early year 6.0l

[HUMTECH]

I test coils by swapping them with another cylinder and see if the misfire follows the coil

[Magnacharged H2]

I havent had time to do much else on the truck , but did download the last freeze frame from my scanner. Engine light only comes on after it sits and idles. If I clear the code while driving it never comes on.
anyone read this Thanks

P0300 random misfire
fuel sys 1 OL
fuel sys 2 OL
calc load % 3.1
ect *c 71
stft b1 0.0
lift b1 8.6
stft b2 0.0
lift b2 14.1
map 42
eng rpm 708
veh speed 0
maf 8.78
tps 9.8