Your Ford Explorer might have a problem with the EGR valve and/or the EGR system; but you'll also want to make sure your 1995 Ford Explorer's fuel/air mixture is correct.
The determination of whether your Ford's EGR valve is working properly should be reflected by the smog check NO (NOx) numbers. First make sure the EGR valve is working properly; it opens and closes without sticking. When your Ford's EGR valve is opened engine idle speed should lower down to where the engine is about to stall; this indicates enough exhaust is passing through to the intake manifold, and also ensure there is vacuum getting to the EGR transducer and that the transducer is allowing EGR vacuum flow while the engine is running above 2000-2500 rpm. This test may require the Ford Explorer be in a drive gear (your Explorer is equipped with a back-pressure EGR valve; the engine needs to be under a certain amount of load in order to open the EGR valve. So you may need to apply parking brakes, shift into gear and then apply slight gas during the EGR valve functional test. Do this procedure at your own risk! As you can see there is the possibility of loosing control of your SUV if performing this test alone. At the smog repair station this test would be conducted only on a dynamometer.
If your SUV's EGR valve/system checks out OK, move on to fuel/air mixture. You want to make sure the oxygen sensor is working properly, your Ford's emissions computer is receiving the signals from the oxygen sensor, 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. The feed back test will utilize a 5-gas analyzer (usually the smog machine) and propane. The smog technician will add propane to your Ford Explorer's intake system and ensure the oxygen sensor is reading this introduction as an increase in CO, and ordering the computer to decrease fuel delivery at the instant propane is added to the system. At the end of the feedback test it will be know whether the high NO fault your Ford Explorer failed the smog inspection for is air/fuel system related or EGR related.
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.
The check engine light being on indicates there are stored trouble codes within the ECU (engine control unit). Using a OBD-I scan tool you will be able to extract the trouble code(s) which will indicate the component or emission system responsible for the light illuminating. The problem may or may not be related to the EGR system.
For more High NO Failures follow this link.
