It's a 3.0, and the test light comes on sometimes, sometimes not. We have replaced, literally, everything under the hood. Dist (cap and rotor also), module, O-2 sensors, ECU, coil, coil capacitor, all sensors... and on and on. I bought the car with the issue and was told it had just started randomnly. The car starts and will run PERFECT, even drive PERFECT, for 10 to 15 minutes, then it will start to lose spark, I have checked the fuel pressure, it is perfect in all cases, I have also looked at the spark (holding a plug against a ground with a wire on it while the engine was running), when the problem starts to occure the fat blue steady spark becomes a weak, light blue, eradic spark. I had it on a scan machine today and it reported no 0-2 sensor on bank 1, out of range reading on bank 2, lean condition and out of range reading on the water temp sensor. Replaced both 0-2s and the water temp sensor, no change. Tommorow it goes to a professional shop and if they cant fix it this low miles, pristine Mercury Sable may meet its maker, help it live! | 
