Fuel leaking from near the tailpipe and black smoke coming from the vehicle's exhaust system are both common symptoms of a bad fuel pressure regulator. A worn out or faulty regulator may also cause the check engine light to turn on or the engine compartment to smell of gasoline.
In some cases, a bad regulator leads to gas leaking into the engine vacuum supply hose. In this case, the leak is not visible, but it can lead to any number of different driving issues.
The fuel pressure regulator helps control the fuel pressure and the amount of fuel in the engine, which ensures that the fuel injectors function properly. When the pressure regulator fails, the excess fuel isn't taken from the engine back to the fuel tank, which causes the engine to flood. One sign of a flooded engine is if the driver's compartment smells of gasoline.
A flooded engine is the root cause behind most of the common symptoms, such as black smoke coming from the exhaust, which is caused by the engine being unable to properly burn all of the excess fuel. The incomplete burning of the fuel may also cause the vehicle to fail an emissions test and also leads to decreased gas mileage due to the excess fuel in the engine.