I purchased the Holley HP MPFI system and just went to the lake with it. The O2 sensor burned out immediately. I stopped by Bergeron on my way back to the lake and he said they have never found a good way to run O2 sensors in a marine exhaust. He had one there that was ran on a dyno then the fuel map was set and shipped back. On my system I machined in the O2 sensor right between the snail and the manifold of a BBC. Phil said water will still get up over the snail and knock out the sensor. Maybe my manifolds had a leak on the inside between the snail and log?? Has anyone ran an O2 sensor in an EFI on a marine engine? What exhausts are the best? I would REALLY prefer to run this brand new holley EFI system in closed loop and not set the fuel map and use the O2 sensor as only a sensor..