It may very well be the EGR valve, but I want you to make sure your 1994
Dodge Dakota'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
Dodge Dakota 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 Dodge Dakota's EGR
valve is working properly should be reflected by the smog check NO (NOx)
numbers.
Not knowing what the functional failure was for I can not suggest whether
it's causing your Dodge's high NO fault so I'll focus on the two problems I
mentioned above. First make sure the EGR valve is working properly; it opens
and closes without sticking. When your Dodge'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 Dodge Dakota 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 1994 Dodge Dakota'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 Dodge'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 Dodge Dakota'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 Dodge Dakota failed the smog
inspection for is air/fuel system related or EGR related; or perhaps some
other problem all together. Best of luck.
