In the last month I've replaced my radiator, flushed the system, recharged the AC, thermostat, O2 sensor, heater core, water and PS pumps, TBI gasket, plugs, wires, ICM, distrib. cap, wires, ALL belts, and most hoses, new 'earl and a K&N. Why now does my service engine light come on everytime I drive more than 5 miles? I have an '87 with 78K orig. mi. on it. The light never came on before. I do need to replace my rear main seal, but the leak is minimal so I have'nt messed with it yet.