Hi all just helped some friends get their 2012 247 LXV back on the water. They had the tell tail burn marks on the catalytic converters, so bad cats. The computer was going into limp mode after running for about 3 minutes of run time. Here's what we found out and what we did to get them going. So we found out that the burn marks are from water jacket failure. The exhaust lining cracks and starts to leak water into the collector just before the catalyst. What happens then is the water is spraying on both the pre and the post O2 sensors and trips the computer. The burn marks are from the exhaust leaking into the water jacket.
We removed the headers and punched out the catalyst and could see the holes in the water jacket. So we cut the converters open and replaced the inner lining then welded them back together. We also did a muffler delete at the same time. They purchased a pair of oxygen sensors simulators from Magnum Tuning US. We had to reset the the simulators to .45 volts from the .95 volts that they come preset. I think the voltage is lower because of the much cooler exhaust temperature being water cooled. http://Magnumtuning.com we started it up today and is running fine and no service lights on the dash anymore.