Originally Posted by
REM
Hmmmmm, yes - this was my first thought - IE the misfire causing the rich condition on the cat - this motor is a new motor from the exact catastrophic engine failure you mentioned - a leaking intake gasket causing a very slow coolant leak which during the covid shut down got driven less and the owner ( not me ) started it and broke a rod from a coolant hydraulic lock - broke the rod in 5 pieces and broke the piston into two large pieces - crack right through the pin boss. I used the new and improved MAHLE intake gasket ( was wondering if the manifold was warped from the previous really bad goo gasket - was completely deteriorated from the red coolant) . My intention was to put a new spider in it and if that didnt fix it was going to surface the manifold and put some new gaskets on it. I did put the spider in it to no effect . This motor probably has 5K on it since rebuild..