Rich Fuel Condition
A rich fuel condition will likely result in a faulty catalytic converter. This is because the unburned fuel is entering the converter and then burning. This will result in a sulfur smell coming from the tailpipe. This also increases the temperature and burns the substrate reducing the efficiency. It is also likely that this converter will clog from this melting substrate.
So the perfect blend of air to fuel mixture or stoichiometric air fuel ratio is 14.7:1. This is when there is just enough air (14.7 parts) to burn one mass or part of fuel with no excess oxygen or fuel left over. A complete burn. These are a few things to check when a rich fuel condition is suspected.
Fuel Injectors: Fuel injectors are electromechanical devices that atomize pressurized fuel from the fuel rail. They become clogged with deposits that form as the fuel dries in the injectors hot tip after turning off the engine. They clog in time and a fuel injector cleaning is necessary. A clogged injector results in a lean misfire and unburned fuel to flowing into the exhaust system and damaging the catalytic converter. They can also leak or drip fuel. This can be diagnosed with a fuel pressure kit and a leak down test.
Fuel Pressure Regulator: A fuel pressure regulator provides a constant fuel pressure to the fuel injectors even though an engine may operate under different loads and operating conditions. A traditional regulator contains a vacuum operated diaphragm. It is controlled by manifold vacuum that would vary pressure to compensate for increased or decreased demand. As the driver accelerates the pressure in the manifold drops and the regulator provides increased fuel pressure for the increased demand. Electronic regulators do the same thing with more precise computer control.
Engine Coolant Temperature Sensor: The ECT is tasked with informing the engine control unit with the engines current operating temperature. This is important to fuel trim because a cold engine requires a richer fuel mixture. If the ECT were faulty and the PCM were receiving a signal informing it of a colder than actual engine the fuel trim would be enriched. This signal will also effect the automatic transmissions TCC torque converter clutch.
Thermostat: The thermostat effects on the engines coolant temperature as it opens and closes. A stuck closed thermostat would result in an overheated engine. A stuck open thermostat will result in a richer than normal fuel mixture because the engine would not likely reach operating temperature.
Oxygen and Air Fuel Sensors: A faulty oxygen sensor will cause an engine to run rich. Use a scan tool to read the oxygen sensors output. An oxygen sensor or O2 sensor sending the wrong signal to the engine control module will result in a rich fuel condition. Symptoms of a rich fuel condition include black smoke coming from the exhaust, fouled spark plugs, and poor engine performance.
