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Forum > Failed Smog Test > Question

What Causes Black Smoke Coming From Tailpipe?

My car failed the smog check because of black smoke coming from the tailpipe during the visual smog test. Everything else passed. How can I get it to pass the smog inspection?

Answer:

What causes excessive black smoke? Black smoke coming from your vehicle's tailpipe may indicate one of two things. 1. Your car or trucks engine is not burning fuel properly, leaving behind high amounts of Carbon Monoxide (CO), resulting in excessive black smoke being emitted from the tailpipe. These vehicles will experience increased fuel consumption as well. 2. Engine oil is seeping into the combustion chambers. Oil is mixing with the fuel & air mixture, leaving behind high amounts of carbon, seen as excessive black smoke being emitted from the tailpipe. Oil seepage may occur due to defective piston rings, valve seals, or Positive Crank Ventilation (PCV) System. posted by SmogTips Support

Your vehicle may have very well passed the emissions portion of the smog check however it is possible CO was still high (as well as HC). This is an indication of an emissions problem and will require diagnosis. As mentioned earlier we'd recommend starting with ensuring fuel mixture is proper and your vehicle is not suffering from a "rich fuel" mixture problem. posted by SmogTips Support

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