Black smoke from exhaust

The most common root causes of a bad air-to-fuel ratio are bad injectors, a bad injector pump, a bad or dirty air filter, a faulty EGR valve, or a bad turbocharger. These are some of the easier fixes for black smoke. Some other more complex engine issues that may cause black smoke include incorrect timing, incorrect valve clearance, bad fuel, carbon buildup in combustion space, bad cylinder compression, carbon buildup in the intake manifolds and other engine tuneup-related problems.