It may very well be the EGR valve, but I want you to make sure your 1993
Ford Explorer's fuel/air mixture is correct as well. I'm going to assume the
functional failure was for a component other then the EGR valve since your
Ford Explorer was administered the Enhanced Smog Check (dynamometer driven)
which does not physically check the EGR valve for proper operation; instead
it is checked visually. 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 (manually) engine
idle speed should lower down to where the engine is about to die; 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 truck be in a drive gear as your Ford Explorer is
equipped with a backpressure 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 truck if performing
this test alone. At the smog repair station this test would be conducted
only on a dynamometer.
If your truck'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 Ranger'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 Ranger failed the smog inspection for is air/fuel system related or EGR
related; or perhaps some other problem all together.
