Mercury Repair Questions? Ask a Mechanic for Answers ASAP
Do you have a scan tool that will check fuel trims? It's possible that you have a faulty engine coolant temperature sensor that is making the car lean out too much when it is hot because of that coolant sensor. The only way to diagnose this for sure would be with a scan tool.
You could also try the following with a multimeter if you don't have access to a scan tool:
Monitor ECT voltages on DATA (if equipped) and verify with a voltmeter on the signal wire at sensor while connected. With engine warm, voltage should read less than 0.7 volts on all engines. If out of range, check to see if ECT is metal or plastic. A very high failure rate on plastic sensors has been documented. There is a very LOW failure rate on original metal style sensors. If the body of the sensor is plastic and the voltage does not accurately reflect true engine temperature, locate and replace with an original style brass bodied sensor.
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