Yes, a Fuel Pump can indeed cause poor idle quality in your engine; this is usually related to the fuel supply to the engine being out of order. If the fuel pump starts malfunctioning or loses its efficiency, it may fail to maintain a constant pressure and, hence, directly impact the performance of the engine at idle. For instance, many vehicles experience rough idling, stalling, or hesitation if the fuel pressure falls by even as much as 5 to 10 psi. During fuel pump failure in a Honda Civic, fuel pressure can easily fluctuate. Such kind of fluctuation in pressure changes the combustion process, furthering the cause of an excessively rough idle, noticeably while the engine is thoroughly warm. This will, in turn, affect the amount of fuel the fuel injectors receive, thus directly impacting the air-fuel mixture and combustion. The resultant conditions are running lean or rich, both of which are capable of causing a rough engine idle.
In one recent report, Ford recalled several of its models due to fuel pumps causing poor idle quality and stalling. It was learned that fuel pump failures led to erratic fuel delivery, which caused significant idle quality issues, especially in turbocharged engine Ford F-150 trucks.
To understand how a faulty fuel pump would affect idle quality, consider the pressure that a normal fuel pump would maintain. Most vehicles need fuel pressure in a range of 30-60 psi to operate efficiently. If the pressure falls below this range, it will be hard for the engine to maintain smooth idle and may stall. A symptom for any faulty pump is a loss of fuel pressure; using a fuel pressure gauge, measurements that denote inconsistencies are those which, in turn, result in an idle problem.
Fuel pumps worn out can also develop faults inside them, such as a clogged filter or a motor, and are unable to pump the required amount of fuel flow to the engine. The wear and tear on the fuel pump motor can eventually cause it to overheat, which may result in intermittent operation. This sometimes results in a rough idling condition, especially at an operational temperature of the engine. For instance, most of the time, owners of the Toyota Corolla will find their fuel pumps faulty whenever there is a case of rough idling, leading to inconsistent fuel delivery during low-speed idling.
The check engine light may also appear in case of fuel pump problems or the occurrence of trouble codes related to fuel pressure, as the OBD-II scanner detects. In most cases, the code will tell that the fuel system operates out of the set parameters, such as low fuel pressure or an inconsistent flow of fuel. When the pump is almost completely dead, it may cause the vehicle to have difficulty starting, idling, or even accelerating, further putting into view the importance of regular fuel pump inspection.
This also occurs in cases where the fuel filter becomes clogged with debris or contaminants and forces the fuel pump to work harder to push fuel through the system. This additional effort impacts the efficiency of the pump and, again, results in similar symptoms of rough idle or stalling. Fuel injectors can also be affected as inconsistent fuel delivery will result in misfires and poor combustion.
Poor idle caused by a failing fuel pump normally involves testing the fuel pressure, checking the electricals for any fault or faults in the fuel pump relay, and if necessary, the replacement of the fuel pump or cleaning of the fuel filter. The cost of replacing a fuel pump is quite high, around $200-$600 depending on the car model, but it is vital to make your engine run smoothly again.
This rough idling in your vehicle will be considered a serious issue in cases where the fuel pump is about to fail. Regular maintenance, which includes checking on the fuel pressure and ensuring the proper flow of fuel, may prevent such issues from heightening. Symptoms such as stalling, rough idling, and difficulty starting call for a thorough diagnosis of the fuel system with focus on the Fuel Pump.