Questions and Answers
Omni Is Having An Emission
Q. Hey Vince, 1987 Dodge Omni 2.2 liter, 60,000 miles, carburetor, automatic. I have an emissions question. The Dodge didn't pass. The following are the results for three tests sequentially:
HC CO CO2 NOx 1 1.26 15.16 330.40 2.41 2 .90 17.68 361.90 2.68 3 .79 15.00 2.56 On the first test, the car was just taken in for the test no repairs were done. On the second test, the spark plugs were replaced and the rotor cleaned and oil filled to the mark. Plus the air filter was replaced. There was improvement the HC showed .90 from 1.26 but the CO changed from 15.16 to 17.68 and the NOx from 2.41 to 2.68. The HC decreased and the CO and NOx increased.
On the third test, the accelerator linkage was readjusted so that when the pedal is depressed and let go it returns to a comfortable idle not where it feels like its being depressed. The CCEGR the sensor for the vacuums required for the air injector system and EGR were repaired as the two hoses responsible for the vacuum broke (so they were repaired). And the results show on the third test.
The air pump works but the two diverter valves were not checked. The choke works (it opens after 5 minutes-can't be rich because these cars are designed for efficiency) and is not stuck. Check the air cleaner system; it works too. Can you tell me what is going on?
Bob
A. HC is unburned hydrocarbons (lean mixture), CO is carbon monoxide (rich mixture) and NOx is nitrogen oxides. These are bad, you want these numbers as low as possible. CO2 is good. The higher the CO2, the more efficiently the engine is operating.
I don't know what state you are in or what the emissions limits there are, but from the readings I can get a good idea of what's happening.
A properly adjusted air/fuel mixture will result in low HC and CO readings. Other things that will effect the HC and CO readings would be a vacuum leak and a catalytic converter not working.
Test two indicates that the spark plugs were in need of replacing. Since the HC went down and CO went up the spark plugs are burning the fuel more completely. As indicated by a higher CO2 reading.
In test three, I see the idle speed had an effect on the emissions. From these readings the idle speed was too high. At this point I would adjust the carburetor and that will get the emissions within specifications.
The NOx is relatively unaffected because the main component for reducing NOx emissions is the EGR valve. Air is 80% nitrogen and, naturally, it gets burned in the engine. The thing is, it takes a high temperature to do it. So the EGR dumps exhaust gas into the intake to cool off combustion temperatures and reduce the formation of NOx. So in order to reduce the NOx levels, you need to look at the EGR system. Perhaps a clogged EGR passage or a bad EGR valve.
Additional Information provided courtesy of ALLDATA
