A faulty fuel pump may make an engine run rich due to its inability to pump the right amount of fuel into the combustion chamber. An engine requires a specific air-to-fuel ratio of 14.7:1 for its efficient running. A malfunctioning pump will disrupt this ratio and result in a mixture with too much fuel and less air, thus being “rich.”
Leaking fuel pumps are the most common causes of this problem. A defective or worn-out pump may allow fuel to bypass its internal elements and flood the fuel system. For example, leaks that increase the delivery of fuel by just 10% can easily exceed the combustion process, with unburned fuel coming out of the exhaust. This mostly generates a rich mixture error code in the onboard diagnostics system of the vehicle.
Rich running can also be caused by clogged or failing fuel return lines. If the fuel pump provides more fuel than required yet cannot return the excess due to blockage, the injectors spray more fuel than needed. Most mechanics can diagnose this issue by examining the fuel pressure, which may be above the standard range of 40–60 PSI in such instances.
Things get more complicated when it’s the fuel pump pressure regulators that malfunction in concert with the pump. A failing regulator incapable of restricting pressure will result in higher-than-necessary fuel delivery. Testing the fuel pressure regulator along with the pump is the recommended procedure among automotive technicians to verify if it works within the manufacturer’s specified parameters. Pressure readings above 60 PSI often indicate a problem with either the pump or the regulator.
Excess fuel in the combustion chamber causes noticeable symptoms, including black smoke from the exhaust, reduced fuel efficiency, and increased carbon deposits on spark plugs. John Carter, a veteran mechanic, states, “Running rich is not just a performance issue—it’s a long-term engine health problem. A faulty fuel pump can cause costly repairs if ignored.”
Regular maintenance, such as fuel filter replacement every 20,000 to 30,000 miles, can lower the chances of any issues regarding the pump since it prevents possible debris from entering the system. Neglecting symptoms will only lead to worse problems, which include a damaged catalytic converter; the replacement for this could be over $1,000.
Replacing a malfunctioning Fuel Pump generally costs in the range of $300 to $900, depending on the car model and labor costs. A good-quality pump replacement will restore appropriate fuel delivery and avoid the engine running rich. For a quality replacement, check Fuel Pump to ensure the engine continues to perform optimally.