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1992 Dodge Dakota Failed Smog for Very High HC
I have a 1992 Dodge Dakota truck that failed the smog test. The HC emissions were very high... 854 ppm at idle. The last time my truck was smog checked it passed by a few points, without a tune up befire the smog test. This time I did a tune up first. I replaced the spark plugs, sprak plug wires, distributor cap, and rotor. I also used fresh gas. The truck also needed a new brake booster and brake pads, so I did that about 2 weeks before the smog inspection.
I was suprised when the smog tech said my Dakota failed the test. I thought for sure it would pass with the tune up that I had done. So my question is could I have done something incorrectly with the plug wires or even turned the ignition rotor the wrong way? Please, I need your professional opinion on the matter. Thank you for your time.
Answer:
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Your Dodge Dakota failed the smog test with very high HC emissions. Hydrocarbon (HC) is basically raw fuel, otherwise known as gasoline. The main reason your Dodge Dakota would fail the smog check because of high HC would be defective spark delivery, but the fuel system has a lot to do with it as well. A "rich" or "lean" fuel mixture would contribute to high HC as well. Since having replaced your Dakota's brake booster, we must recommend that you ensure the brake booster is not creating a vacuum leak; since it relies on manifold vacuum to assist brake function. A vacuum leak will cause high HC, especially at idle.
Begin with inspecting your Dodge Dakota's ignition system, ie. spark plugs, wires, distributor, and ignition timing. Make sure the spark plug wires are affixed firmly. If everything looks ok, move on to the more complicated inspection of the fuel delivery system, ie oxygen sensor (s), engine coolant temperature sensor, mass air flow sensor. These components will require some auto emissions know-how and proper inspection tools. It is best left up to an experienced smog check technician.
Follow the link below for a full list of High HC Causing Problems:
What Causes High HC?
posted by SmogTips Support
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