Your Ford Explorer is not equipped with an EGR system. NO control relies on proper fuel control, CAT operation and cylinder compression (engine temperature). We recommend inspecting your Ford Explorer's "fuel feedback" system. This includes ensuring the oxygen sensors are working properly, the ECM system is receiving the signals from the oxygen sensors, the computer is computing the data properly and sending the correct signals to the fuel injectors to either increase or decrease fuel delivery to the combustion chambers. A lean fuel condition will cause high NOx.
Some of the other emission sensors on your Ford Explorer which should be inspected and which also play a significant role in determining air/fuel ratio are the Engine Coolant Temperature (ECT) sensor and the Mass Air Flow (MAF) sensor. If your Explorer's engine coolant temperature sensor is not operating properly (not sending the correct voltage signal to the Engine Control Module) the ECM will not be able to properly calculate how much fuel to deliver to the combustion chambers. The ECM may lean out the fuel mixture, causing the high NO. The MAF (mass air flow)sensor measures the amount of air entering the intake manifold. This sensor must send accurate information to the ECM as well, in order for the ECM to calculate exactly how much fuel to add to the air entering the combustion chambers.
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