Could anyone tell me why the Sunpro Supertach 2 -CP7901 will not function in my 92 Corolla with a 4AFE engine? I followed all of the directions and the red wire is to the positive and the black to the negative and the green to the -G at the diagnostic terminal. Is this tach simply not compatible with this engine? At first the needle just dipped a little bit and now it waits for 30 seconds or so and then proceeds backward to 8000rpm and sits there till I turn off the engine. I sure need some help on this one.