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Forum > Failed Smog Test > Question

1994 Dodge Dakota 4 cyl 2.5 liters high NO, what would cause this?

My Dodge truck failed functional check and emissions test. It failed the NO (ppm) at 15 MPH it was 596 the Max is 527 and the Ave is 187. Can it be my EGR valve. Can you help my 94 Dodge Dakota pass smog test?
Answer:

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.


posted by SmogTips Support

 

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