2000 sport 4.0L AW4 NV242 running 33's and 4:11s
Seems my P0306 code has been a burnt exhaust valve all along. I did everything short of doing a compression test and pulling the head. I even changed out ECU with a new one and changed the valve springs on #6. Finally got a compression tester and only got 30 PSI. Crap! I thought I'd have a cracked head before something like that would happen.

Short story long I have a 99 4.0L sitting in the driveway. Pulled the head and it looks great. I thought of just pulling the 0331 head and swapping exhaust valves but I seem to recall they are smaller.
So I'm thinking of just swapping in the 99 after a hot tank and new valve seals. Other than my coil pack will need some kind of brace to stop it from vibrating off the plugs, is there anything else I should be on the lookout for?
Will I have any problems running the larger exhaust valves on my emissions stuff? It has the Federal system so only 2 o2 sensors and 1 catalytic converter. Will my mileage change. Can't get any worse but can I expect less than original?
Or should I just run the 0331 head until I can afford to get a new Clearwater head?

 

everyone that i have seen who have swapped in a 99 or later head onto our 0331's have not had an issue with the emissions. Other than having to fab a bracket for the coil pack to mount to. Get it tanked and ready for use.

 

A really lean burn will wipe an exhaust valve quick, check that injector (#6) for operation & flow if you plan to reuse it.