When I checked my timing chain elongation using the 2mm method, I came up with a value of 19 degrees BEFORE top dead center. The spec for my car is 11 degrees ATDC. The car runs, but not great. When I set IP timing to 24 degrees BTDC, the car crapped black smoke and had almost no power. Lining up th cam marks, the value is 7 degrees ATDC. what could account for such a discrepancy? The car is an 83 240d.