Fuel systems have become increasingly sophisticated as OEMs seek to enhance fuel efficiency and engine performance. Many technicians are returning brand new fuel pumps as defective, only to discover that the root cause of the problem was a bad crankshaft sensor or fuel pump relay. So, to prevent some of the most typical technician diagnostic errors, let’s look at some of today’s most popular fuel systems, their failures, and “magic bullet remedies.”
The PCM must properly measure the vehicle’s fuel level to detect evaporative leaks. As a result, current fuel gauge designs generally include a small module that computes the actual gasoline level in the tank in 20 minutes. Without this understanding, many novice mechanics may presume a tank is half-full when it is not. A fuel pump inlet strainer may also be fitted, interfering with the float arm travel of the fuel level sensor, causing an optimistic result. Dings in the fuel tank can potentially produce misleading readings by raising the fuel level sensor and fuel pump inlet filter. In any scenario, the engine may be out of gas due to a faulty fuel gauge on the instrument panel.
Normally, most fuel pumps make an audible noise for a few seconds after the ignition is turned on. The comparatively quiet two-speed gasoline pumps found in many foreign and domestic vehicles may mislead a technician. Given that the fuel pump speed is dependent on engine speed and load, a fuel pressure gauge should be used to verify that the pump is running and supplying the proper fuel pressure. If the gauge doesn’t show fuel pressure, know how most fuel pumps work. To clear air from the fuel injectors and provide proper fuel pressure for the engine’s cranking cycle, the PCM briefly engages the fuel pump. After starting the engine, the PCM “looks” for cranking speed and ignition triggering. If one or both of these inputs are missing, the PCM may turn off the fuel pump. A malfunctioning ignition system or a malfunctioning fuel pump are prevented by this exact sequence of events.
A gasoline pump relay is a high-current switch controlled by a PCM low-current circuit. The contact contacts on the fuel pump relay wear out with time, reducing the electric current supply to the fuel pump. Because reduced current flow slows the fuel pump, the engine may struggle to start in cold weather when the battery voltage is low.
Stalling and surging are commonly caused by a dirty or malfunctioning air flow sensor. Many imports have a vane-type airflow sensor to activate the fuel pump relay. If the duct between the air-flow sensor and the throttle plate has an air leak, the sensor won’t trigger the fuel pump, and the engine won’t start. Remove the air filter and manually open the airflow sensor vane while cranking. It is the air duct that has a problem, not the fuel pump. Clogged fuel filters accelerate fuel pump wear; thus they should be changed every 30,000 miles or when a new fuel pump is installed.
Faulty Fuel Pumps:
How do you diagnose a cranking but not starting the engine? If ignition and compression are both good, the obvious culprit is fuel. What’s wrong with the fuel delivery system? The most probable causes are:
A broken fuel pump
Blocked fuel filter
A weak pump or a clogged pipe; alternatively
No pulse to injectors
The PCM usually energizes the pump via a relay. It is possible to connect an oil pressure switch or an inertia safety switch to the pump circuit. Before making any assumptions, look at a wiring diagram. Low voltage in the pump’s power supply circuit or high resistance in the pump’s ground circuit are examples of electrical issues. The pump may not run or spin rapidly enough to create normal fuel pressure.
Identifying A Faulty Fuel Pump:
Dead Head Pressure: Checks the fuel pump’s maximum output pressure. With the return line blocked, the pump should create a much higher pressure than typical. The pump may not be able to supply enough fuel at higher engine speeds if the return line is obstructed. One cause could be a worn pump, low voltage at the pump, a clogged fuel filter, a clogged fuel line, or an almost empty tank. Normal-pressure fuel pumps can cause drivability issues if they can’t supply adequate fuel volume to the engine. A fuel volume test may be the best technique to assess the pump’s health. A fuel volume test examines the fuel provided over time. To test the fuel supply line, either connect a fuel flow gauge or detach the fuel return line from the fuel pressure regulator and connect a hose from the regulator to a big container. Watch out for open sparks or flames while performing this test. Energize the pump and measure the volume of fuel supplied over the designated time. A decent pump should supply a quart of fuel in 30 seconds or less. Fuel pump returns are mostly due to misdiagnosis. If the engine runs but has poor drivability, try to eliminate likely caused by:
Testing the OBD system
Testing the ignition system
Vacuum Leak Checking
Inspecting EGR and PCV systems
Testing power balance
Fuel Pump Failures:
Replacing an electric fuel pump won’t fix a no-fuel issue because the pump is only part of the fuel distribution system. To properly service the car, a technician must first detect the fuel issue. It can’t run without electricity, thus anything that interrupts the flow of current or voltage will stop it. rusted, loose, or broken wiring.
A dirty tank might block the pickup strainer, harm the pump, and/or stick open the pump’s check valve; which can cause a hard-starting condition due to loss of pressure when the engine is shut off. If a pump failure is caused by dirt or sediment in the tank, the tank should be completely cleaned to avoid repeat failures.
Fix Fuel Pump
Corrosion inside the tank creates rust, which can flake off and clog the pickup strainer, as well as harm the pump. Condensation occurs in chilly, humid conditions when the gasoline tank is low. Keeping the tank full reduces condensation. Replace the tank if it is corroded or leaks.
Normal wear: Most pumps are built to last, but they are lubricated and cooled by the fuel. Frequent driving with low gasoline can deplete the pump of lubrication and cooling, causing premature wear or possibly pump damage.
Symptoms of a failure
Noise can indicate severe pump wear. Some pumps are naturally noisier than others, due to how they’re situated inside the tank. A loose or missing rubber noise insulator around the pump or physical contact with the tank bottom or tank baffles might produce noise.