Home › Forums › Stay Dirty Lounge › Service and Repair Questions Answered Here › Ash / Crust on only one Spark Plug Bank › Reply To: Ash / Crust on only one Spark Plug Bank March 7, 2021 at 5:11 am #989285 Richard KirshyParticipant Might try doing a leak down test to see if there is excessive bypass Another possibility, you could be dealing with clogged oil rings