Supercharged Riveria Problem/Question

[mpneroz]

Bought a solid rust free silver 1996 Riviera that came out of Florida.  Body, floors and frame looked new.  Had a blown SC 3800 series 2 engine.  The engine block cracked because the people who drove it up here from Florida kept adding water to it during one of our brutal Pennsylvania winters instead of fixing a water pump leak.  Bought it for $500 and replaced the engine with the exact engine.  Shook it down, ran great  and my son in law wanted it so I gave it to him for what I had in it.  

 

Car ran great initially but a problem developed and under load up a steep grade the car would miss fire and have no power then straighten out and run ok.  Check engine light would flash.  Found cracks in the heads and replaced them with a nice rebuilt set inexpensively.  Car then back into service all went well. Began to throw a misfire code cylinder 3 and when we pulled the plug it was starting to burn on the tip like with the previous heads.  Changed mas air sensor, new plug put in car was running great again.  I shook it down and told my daughter to take it home, about a 45 min trip.  I ran it hard and it seemed great.  She called me in route and said the car had done the same thing.  So where to go from here?  What else would cause the lean condition needed to ruin plug tips and cause misfire?  Car now running worse and I am back to square one.  HELP! 

[Guest Jilla 66 rivi GS]

I would check the ignition coils. two cylinders per coil, it is possible for one side of the coil to work and not the other. Also, make sure it has the proper thermostat in it.They are designed to run at a certain temp. my 96 has 234k miles. mostly original. couple waterpumps, serpentine belts, plugs, one coil...otherwise completely all original.