Hi, I thing that trying to ignite at TDC is complicating things for you, the spak should occur before it hits TDC at about 28 degrees, well that is on a 2 stroke gas engine and I think it would be similar on a four stroker, try to move your sensor by rotating it to clokwise about 3/8 to 1/2 inch so it ignites before it hits TDC and see what happens