Hey guys, i know, the title sounds scary. I don't think its as bad as it sounds. I'm restoring a viggen, just recently, under hard accelleration, it will loose power. It sounds very similar to a exhaust rattle, but thats not what it is. Its coming from the engine. Somthing is making it detonate. The M.I.L is off. I havent really started in depth diag, just sort of looking for a start point. it did have 1/4 tank of 87 in it, then i filled the rest with 93 octane (whats recommended) and wondering if that could cause it, but i highly doubt it. any ideas guys? I start my Diagnostics tomorrow.

 

Run it empty and refill with 93. Change the spark plugs. See if it happens again.