Trystan Casey
Testing an electric fuel pump can be done in several ways, depending on the equipment available and the suspected fault. A common issue with fuel pumps is debris blocking the mechanism, which can cause trouble accelerating and other symptoms that suggest your car is not getting enough fuel. Before testing, it is important to check the fuse and fuel filter, as well as the wiring, to ensure these are not the root cause of the problem. If these look fine, you can perform a fuel pressure test, a fuel pump volume test, or a voltage test.
A fuel pressure test involves using a pressure gauge to measure the pressure at the fuel rail, which should meet the manufacturer's specifications. A fuel pump volume test can be performed by connecting a gauge and placing the bleed end of its hose into a clean container. Without starting the engine, you can then activate the pump for 15 seconds while holding down the relief valve. A voltage test can be performed by connecting the positive lead of a voltmeter to the battery and the negative lead to the positive wire at the fuel pump connector.
It is important to note that other issues can mimic a faulty fuel pump, so a thorough diagnosis is necessary to ensure the pump is the problem before replacing it.
| Characteristics | Values |
|---|---|
| Test type | Fuel pump volume test, fuel pressure test, voltage test, oscilloscope test |
| Tools required | Fuel pressure gauge, voltmeter, oscilloscope, fire extinguisher |
| Pre-test checks | Check the fuse, fuel filter, wiring, and pump |
| Test procedure | Locate the fuel pump test point, hook up the pressure gauge, rev the engine, check the pressure, perform a voltage test, inspect for leaks or corrosion |
| Post-test actions | If pressure is low, replace the fuel filter and retest; if voltage is low, find the issue within the wires; if the voltage is correct, perform a voltage drop test |
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What You'll Learn
Check the fuel pump relay and fuse for any issues
The fuel pump relay is an electromagnetic switch that uses low current to control a higher current circuit. It is a necessary component for the combustion engine model to function, as it ensures the engine gets the fuel it needs. The relay can eventually fail, causing the fuel pump to malfunction. Some common symptoms of a failing fuel pump relay include ignition issues, the fuel pump running continuously, and an illuminated check engine light.
Before checking your fuel pump, locate the fuse that corresponds to the pump and remove it to inspect for any burn marks or breaks. If the fuse looks fine, check the voltage at the pump to ensure the charge leaving the fuse is reaching the pump. If the voltage is low, you will need to find the issue within the wires. If the voltage is correct, perform a voltage drop test.
To perform a voltage drop test, connect the positive lead of the voltmeter to the battery and the negative lead to the positive wire at the fuel pump connector. Repeat for the negative side. If you have more than a 0.5-volt drop on either side of the circuit, you will need to repair this first.
You can also test the fuel pump relay with a multimeter. First, take the fuel pump relay out of your vehicle and clean and inspect it. Then, use the multimeter to check the resistance going through the relay's circuit to see if it is faulty. If you detect zero ohms or any resistance value, your fuel pump relay has shorted power pins and needs to be replaced.
Another way to test the fuel pump relay is to temporarily swap it with another relay from the power distribution box. If the fuel pump runs with the alternate relay installed, the original fuel pump relay needs to be replaced.
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Inspect the fuel pump electrical circuit
Inspecting the fuel pump electrical circuit is a crucial step in diagnosing a faulty electric fuel pump. Here's a detailed guide on how to do it:
Firstly, locate the fuse box, which is usually in the engine compartment, and find the fuse associated with the fuel pump. Remove this fuse and carefully examine it for any signs of damage, such as burning or breakage. If the fuse appears faulty, it will need to be replaced with one of the proper amp rating.
Next, check the voltage at the pump to ensure that it is receiving power. If the voltage is low, there may be an issue with the wires, and you should perform a voltage drop test to pinpoint the problem. Connect the positive lead of a voltmeter to the battery's positive terminal and the negative lead to the positive wire at the fuel pump connector. Repeat the process for the negative side. If there is a voltage drop of more than 0.5 volts on either side, the circuit or wires may be faulty and will need repair.
Now, it's time to test the fuel pump relay. With the engine off, locate the fuel pump relay, which is often near the fuel injectors. Have an assistant turn the key in the ignition, and place your hand on the relay. A functional relay will be felt as it clicks on and off.
Additionally, you can use a digital multimeter (DMM) to test the circuit for continuity, power, and ground integrity. This tool will help identify any unwanted excessive resistance that may be causing issues.
If you have access to an oscilloscope, you can also use it to diagnose the fuel pump electrical circuit. An oscilloscope will display voltage signals over time and can help identify issues such as burned-out windings or open circuits.
Remember, it is essential to consult your vehicle's owner's manual for specific instructions and fuse box locations, as they may vary depending on the car model and year.
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Check the fuel pressure
To check the fuel pressure, you will need to get a fuel pressure gauge. These are available at most auto parts stores for $20-30, or you can borrow one from machine shops or auto shops. You will then need to hook up the pressure gauge to the fuel pump test fitting. The test point is usually near the fuel injectors, where the pump hooks up with the filter injector rail. There should be a separation joint or a test port, where the pressure gauge attaches. The location of the fuel pump varies from vehicle to vehicle, so consult your owner's manual for more specific instructions.
With the engine off, install the fuel pressure tester on the test port (which looks like a Schrader valve) on the fuel injector rail. Have your helper turn the key on without starting the engine. Make a note of the fuel pressure, and compare it with the pressure listed in your service manual. If the pressure is too low, replace the fuel filter and retest. If it is still low, you will need to check the voltage at the pump. If the pressure is correct, the problem is elsewhere.
Now, with a helper, rev the engine and check the gauge. Let the engine warm up slightly, then check the pressure at idle speed and at the rated speed listed in your pump specifications. If you don’t know the rated speed, just rev the engine and observe how the pressure reacts. If the needle doesn't move or goes down below specifications, the fuel pump needs to be replaced.
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Conduct a voltage test
Conducting a voltage test on an electric fuel pump is an important step in diagnosing whether it is faulty. Before beginning the test, ensure you have the vehicle's repair information handy, and that you have checked the fuel pump relay and fuse for any issues.
To conduct the voltage test, first locate the wires connected to the fuel pump. In most cases, there are four wires: two to the fuel gauge and two to the pump. The ones with the largest gauge wire are the fuel pump feed wires. Place the black voltmeter lead on a good ground on the frame. With the red positive lead, probe the positive wire terminals while your helper turns the key on. The voltage should be within 0.5 of the battery voltage. If the voltage is low, you will need to find the issue within the wires. If the voltage is correct, you will need to perform a voltage drop test.
To perform a voltage drop test, connect the positive lead of the voltmeter to the battery and the negative lead of the voltmeter to the positive wire at the fuel pump connector. Have a helper cycle the key. You should not see more than a 0.5-volt drop. Repeat this process for the negative side. If you have more than a 0.5-volt drop on either side of the circuit, you will need to repair this first.
If the voltage tests indicate that the pump is receiving the correct voltage, but the pump is still not functioning properly, there may be an issue with the fuel pump itself or another component of the fuel system. In this case, further diagnostics may be required, such as a fuel pressure test or a visual inspection of the fuel pump for any signs of leaks or corrosion.
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Test the pump with gasoline running through it
When testing an electric fuel pump with gasoline running through it, there are several precautions and procedures to follow. Firstly, it's important to understand that these pumps are "push" pumps, not "pull" pumps, so your gas source needs to be able to gravity-feed the pump. These pumps operate at high pressure and high volume, so ensure the output hose is securely fastened. Due to the high-pressure nature of these pumps, they tend to move around a lot when operational, so be sure to clamp the pump securely to your bench before starting.
Safety is paramount when dealing with gasoline and electricity. Minimise sparks when connecting the power source. One effective method is to install a simple 12V on/off switch and secure all wires. Additionally, perform this test in a well-ventilated area, as gasoline fumes are highly flammable. Keep a fire extinguisher nearby as a safety precaution.
To begin the test, locate the fuel pump relay in the fuse box and remove it to inspect for any visible damage. If the relay appears damaged, swap it with a similar relay to determine if the fuel pump functions properly. If the pump is functional with the new relay, you've identified the issue.
Next, check the voltage at the pump's power supply wire with the ignition turned on. A functioning circuit will display a voltage of approximately 12V. If the voltage is lower, there may be an electrical issue affecting the pump's performance. However, if the voltage is within the acceptable range, proceed to perform a voltage drop test. For this test, connect the positive lead of a voltmeter to the battery and the negative lead to the positive wire at the fuel pump connector.
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Frequently asked questions
There are several ways to test an electric fuel pump. One way is to check the fuel pump relay and fuse for any issues. Listen for a buzzing noise near the fuel tank when the ignition is turned on, indicating proper pump operation. You can also utilise a fuel pressure gauge to measure the pressure at the fuel rail, ensuring it meets the manufacturer's specifications.
If your car won't start, struggles to accelerate, or shows signs of not getting enough gas, it could be due to a faulty fuel pump. Other symptoms include a sputtering engine and a strange whining sound from the fuel tank.
First, locate the fuel rail and test port on your car, then turn off the engine and relieve the fuel pressure. Attach the hose and adapter to the gauge and connect it to the test port. Turn on the ignition key without starting the engine and observe the reading on the gauge.
A voltage drop test checks for issues within the wires. Connect the positive lead of the voltmeter to the battery and the negative lead to the positive wire at the fuel pump connector. Have a helper cycle the key. You should not see more than a 0.5-volt drop.
You can use a fuel pressure gauge, a voltmeter, or an oscilloscope to test an electric fuel pump.
