To test a fuel pump, first listen for it humming when the key is turned, then check the fuse and relay; if those are good, use a fuel pressure gauge to check for adequate pressure (around 30+ PSI) and a multimeter to ensure it's getting power and a good ground, as a lack of pressure or power indicates a failing pump, even if it runs.
The best way is to put a fuel pressure gauge on the service port. Check for pressure. Then do a volume test. If there are bubbles in the fuel, the pump is on its way out. Vapor bubbles in the fuel will keep an engine from running. Low pressure will keep an engine from running.
Tools for Testing a Fuel Pump
The main tool you'll want is a fuel pressure gauge, which measures the pressure inside the fuel system. A multimeter is also handy for checking electrical connections and voltage. If you have access to an OBD-II scanner, you can scan for error codes that may point to pump issues.
A clogged fuel filter can mimic fuel pump problems. It is advisable to replace the fuel filter and see if the symptoms persist.
Tap the Fuel Tank
Sometimes, a failing fuel pump can be “encouraged” to work temporarily by giving it a little nudge. Here's how: Locate the fuel tank under your car. Use a rubber mallet or the heel of your shoe to tap the bottom of the fuel tank lightly.
Electrical faults are a major contributor to fuel pump failures, often stemming from issues such as corroded connectors, loose terminals, or damaged wiring.
Use a Fuel Pressure Gauge to Confirm a Faulty Pump. Graduates of auto mechanic school are experts in diagnosing car problems such as faulty fuel pumps, and this is one of the more complex checks they perform. A fuel pressure gauge is connected to the fuel test pressure port on the top of the engine.
Steps to Start a Car with a Failing Fuel Pump
Electrical Issues: Faulty wiring, corroded connections, or blown fuses can disrupt the power supply to the pump, causing it to malfunction or stop working altogether. Overheating: Running a vehicle on low fuel can cause the pump to overheat.
Normally, a working fuel pump will display a resistance ranging from 0.5 to 2 ohms. Should the multimeter indicate infinite resistance, this suggests that the pump may be defective.
As mentioned, having a faulty fuel pump will affect the engine power due to an inadequate gas and fuel mixture. This can result in the inability to turn on the engine because no fuel is injected into it. Even though these parts are built to be durable, they can take damage due to dirt, overload, and wear over time.
The only real way to test for a bad pump is with the right equipment. A combination of diagnostic equipment for reading voltage, resistance, and fuel pressure, along with professional knowledge on the subject, is necessary to make sure the pump is at fault.
Idle vacuum for most engines is about 18 to 22 in. -Hg, but some may produce only 15 to 17 inches at idle. (Remember what we said about experience.) If vacuum is steady and within these ranges, the engine and fuel and ignition systems are operating normally.
This range can vary depending on the make and model of the vehicles, but for most gasoline cars, fuel pressure falls within the range of 30 to 50 PSI. High-performance gasoline engines might require higher fuel pressure, which can go up to 60 PSI or more.
The pump has to work harder to push fuel through the blockage, which increases wear and can lead to premature failure.
Fuel pump failure usually comes from simple wear and tear, but clogged fuel filters, running the tank low and contaminated fuel all speed things up as well because they force the pump to work harder. Also, electrical faults like bad wiring and weak voltage can stop the pump from spinning properly.
It takes gas from the gas tank and sends it to the engine so your car, truck, or SUV can start and run. Your vehicle's fuel pump should last at least 100,000 miles or more.