A backfiring or smoking exhaust can indicate either too much fuel or too little spark, both of which can bring about power loss. A backfire occurs when the fuel-air mixture does not fully ignite in the combustion chamber, but instead pops off elsewhere in the system. Both fuel-air ratio problems and electrical issues can trigger firing foul-ups [sources: Bosch; Salem].
Spark plugs covered with engine oil, ash or other deposits will misfire, as will plugs with partially melted electrodes. Black smoke from your tailpipe might point to spark problems, which can damage your engine, so check them as soon as possible [sources: Bosch; Salem].
Black smoke could also mean that your fuel-air mixture is too gasoline-rich. Time for an adjustment. And if you pop the hood and your engine reeks excessively of eau de Esso, do not try to start it. It's time for a tow [sources: Salem; Sclar].
Conversely, backfiring without black smoke could indicate too little fuel in the mix [source: Salem]. We'll discuss that, too.