* Faulty fuel injector: A faulty fuel injector can cause the engine to inject too much fuel into the cylinders, which can also lead to a rich running condition and excessive exhaust gas.
* Clogged catalytic converter: The catalytic converter helps to clean up the exhaust gases by converting harmful pollutants into less harmful ones. If the catalytic converter is clogged, it can cause the engine to run poorly and produce excessive exhaust gas.
* Vacuum leak: A vacuum leak can cause the engine to run lean (i.e., with too much air and not enough fuel), which can also lead to excessive exhaust gas.
* Head gasket leak: A head gasket leak can allow coolant to enter the combustion chamber, which can cause the engine to run poorly and produce excessive exhaust gas.
