Spark Plug Burn Pattern

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Author Message   Brian (Bthaxton) Member Username: Bthaxton Post Number: 55 Registered: 02-2003 Posted on Friday, January 02, 2004 - 03:05 pm:    Recently I changed the plugs in my '97D1 w/103K miles. As a general practice I always remove the old plugs and arrange them in the order of their respective (former) cylinders. This allows me to see the overall 8-cylinder burn pattern and hopefully diagnose any potential problems. With my last plug change, I noticed all the firing ends were the usual uniformly ash-gray burn color, except for the #4 cylinder (passenger side, 2nd from radiator). This plug's firing end was black. Even stranger still, it was black on only 1/2 of the firing end, as if it was being contaminated from either above (valves), or below (cylider), not both. What could cause this? By the way, I use Bosch Platinum plugs and I "mind the gap" (London Tube joke) very well.   Brian (Bthaxton) Member Username: Bthaxton Post Number: 56 Registered: 02-2003 Posted on Saturday, January 03, 2004 - 03:27 pm:    OK then, how can I tell if I have a malfunctioning valve(s) at that location?   Joey Stompedissel (Huskyboy) New Member Username: Huskyboy Post Number: 13 Registered: 10-2003 Posted on Saturday, January 03, 2004 - 03:37 pm:    Brian, would start with a compression test. And when you do , stand clear of the doors ;) Joey