Ameer Randolph
Testing a fuel pump outside of a car can be done in several ways. One common method is to use a fuel pressure gauge, which can be purchased at most auto parts stores. This gauge is hooked up to the fuel pump test point, and if the needle doesn't move or moves very little, it indicates an issue with the fuel pump. Another approach is to check the fuel pump fuse, as issues with the power supply can often be the culprit. Inspecting the individual circuits and checking the voltage at the pump itself are also important steps in diagnosing fuel pump problems. Additionally, scanning tools or code readers can be used to retrieve information about any issues, and checking fuel pressure and volume can provide further insights.
Testing a Fuel Pump Outside of a Car
| Characteristics | Values |
|---|---|
| Testing the fuel pump fuse | Check the owner's manual for the fuse box location, then find and remove the fuse corresponding to the fuel pump. Inspect it for signs of failure (blown fuses will be broken or burned). |
| Voltage check | Check the voltage at the pump to ensure it is receiving power. Test for source voltage to determine if the charge is reaching the pump. |
| Checking for corroded wires | If there is a volt difference of more than one, it indicates corroded wires or circuit issues. |
| Fuel filter inspection | Remove the filter and drain excess fuel. Use a rubber hose on the filter inlet and blow through it, checking for resistance. Inspect the screen for debris and replace the filter if necessary. |
| Fuel pressure gauge test | Purchase a fuel pressure gauge and hook it up to the fuel pump test point. Have an assistant rev the engine; if the needle doesn't move, the pump may be faulty. |
| Official pressure test | Place a pressure gauge on one side of the pump and a vacuum gauge on the other. Do not blow compressed air into the pump as it may cause damage. |
| Disconnecting the fuel line | Disconnect the fuel line to the carburettor and cover the end with a plastic bag secured by a rubber band. Turn the engine over; if fuel spurts out, there is a carburettor issue. No fuel or a dribble indicates a blockage or leak in the fuel line or a faulty pump. |
| Removing the pump top | Unscrew the central bolt or screw holding the pump top in place (some models may have multiple screws). |
| Checking for leaks | Gaskets, fuel pipes, and seals between the diaphragm and pump body may leak. Diaphragms can also develop small leaks. |
| Testing fuel pressure sensor | Many vehicles have a fuel pressure sensor on the rail, and some have a Schrader valve where a gauge can be connected. Check the specified fuel pressure online and compare. |
| Checking fuel trim | Use a scan tool to check the short-term fuel trim (STFT) parameter. Readings above 10 indicate a potential issue with the fuel pump not delivering enough fuel. |
| Fuel pressure assessment | Check fuel pressure at idle or under load. Continuous fuel systems can be assessed for "dead head" pressure by pinching off the return line. |
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What You'll Learn
Check for a blown fuse
To check for a blown fuse, you must first locate the fuse box. Refer to your owner's manual to find the fuse box in your car. Once located, find the fuse that corresponds with the fuel pump. Pull it out and inspect it for signs of failure. A blown fuse will be broken or burned. If the fuse looks intact, check the rest of the fuses related to the fuel system and replace them if necessary.
If the fuse is indeed blown, this could be a sign of a high amp draw. In this case, you will need to check the individual circuits. Try replacing the blown fuse and attempt to start the vehicle. If the new fuse blows, a direct short is present, and you will need to take your car to a mechanic to get it checked out.
Before taking your car to a mechanic, you can perform some additional checks to diagnose the problem. First, check the voltage at the pump itself. A lack of voltage could indicate an issue with the power supplying the pump. You can also test for source voltage to determine if the charge leaving the fuse is reaching the pump.
Another test you can perform is to disconnect the pump and replace the fuse. Then, turn on the ignition. If the fuse blows, there is a short in the wiring or a faulty relay. If the fuse does not blow, turn off the ignition, reconnect the fuel pump, and turn on the ignition again to see if it pops.
Finally, it is recommended to check the continuity of the wiring and any potential shorting out. You can do this by checking for continuity between the pump fuse and the multi-plug, as well as between the pump fuse terminal and the earth. Additionally, inspect the multi-plug and visible wires for any fraying or shorts.
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Test the fuel pump relay
If you're experiencing issues with your fuel pump, such as no noise coming from it or your engine not starting, there could be a problem with the fuel pump relay, which controls the electric current running through the pump. Luckily, you can easily test and replace the fuel pump relay yourself.
First, turn off your vehicle and remove the key from the ignition. Locate the main fuse box, usually found underneath the hood near the front of your vehicle. There may also be a smaller fuse box under the steering column inside your car. Pull the cover off the fuse box and refer to the diagram to identify the fuel pump relay, which is usually coloured green or grey. If the diagram doesn't show the location, check your vehicle's manual.
Once you've found the fuel pump relay, pull it straight out from the fuse box. Grab it firmly on both sides and pull it straight up and out from the terminals. If it's stuck, try rocking it back and forth gently to loosen the connection. After removing the relay, you can clean and inspect it.
To test the fuel pump relay, use a multimeter to check the resistance going through the relay's circuit. This will help determine if it's faulty. If the relay functions correctly and has the right readings, you may have a different problem with your fuel pump or electrical system.
An alternative method to test the fuel pump relay is to temporarily swap it with another relay from the power distribution box, such as the air conditioning compressor relay, if they share the same design. If your vehicle starts without issues, then the old fuel pump relay is faulty and needs replacement.
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Use a pressure gauge
To test a fuel pump outside of a car, you can use a pressure gauge. This is a good investment as it is useful for most cars and can be purchased for $20-30 at most auto parts stores. If you don't want to buy one, you can also try borrowing one from machine shops or auto shops.
Before you get started, it is important to remember that releasing fuel under pressure can cause fire and injury. So, put safety first. Wear safety glasses and gloves, work in a well-ventilated area, and do not smoke or have anything around that could cause a spark.
Now, follow these steps:
- Park your vehicle on flat ground with the emergency brake set and the engine off. This test is for in-tank fuel pumps only.
- Remove the top of the pump. It is usually held on by a central bolt or screw, except for the SU AUF 700, which is held by three screws.
- Attach the pressure gauge to the test port. Some cars have a pressure port on the engine fuel rail, while others will need an adapter from the test kit attached at the fuel filter or fuel pressure feed line. Most gauges have a quick-disconnect coupler that allows for various adaptors.
- Without starting the engine, turn the ignition key to the "on" position. The gauge should jump up to between 45 psi and 58 psi (DPI) for direct port injection.
- Have a helper rev the engine while you 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 pressure does not increase as you rev the engine, or if the needle doesn't move much or at all, there is a problem with the fuel pump, and it needs to be replaced.
Note that different gauges may have slightly different instructions, and the location of the fuel pump varies from vehicle to vehicle. So, always consult your owner's manual for more specific instructions.
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Check for blockages
If you are experiencing issues with your car's fuel pump, it is important to check for any blockages that may be causing the problem. Here are some detailed steps to help you check for blockages in the fuel pump outside of your car:
Firstly, identify the fuel pump's fuse in the fuse box, as often it is not the pump itself that is faulty, but the power supply. Inspect the fuse for any signs of failure, such as burning or breakage. If the fuse appears damaged, replace it with a new one of the proper amp rating.
Next, check the rest of the fuses related to the fuel system and replace any that are blown. If none of the fuses are blown, proceed to listen for the fuel pump relay clicking by turning the key while the engine is off.
Now, you can eliminate the filter as a potential source of blockage. Remove the filter from the vehicle and drain any excess fuel. Attach a short piece of rubber hose to the filter inlet and blow through it, noting any resistance. Minimal resistance and good airflow indicate that the filter is not clogged. Inspect the screen for any debris, and if necessary, replace the filter.
Additionally, you can use a fuel pressure gauge to check for blockages. Connect the gauge to the fuel pump test point and have an assistant rev the engine. If the needle shows little to no movement, it indicates an issue with the fuel pump, which could be due to a blockage.
Finally, for mechanical fuel pumps, you can check for blockages by observing the fuel flow. If there is no fuel or only a dribble, it suggests a blockage or leak in the fuel line or a faulty fuel pump. Remember to refer to specific instructions for your vehicle's make and model, and always prioritize safety when working with automotive systems.
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Check the fuel pressure
Checking the fuel pressure is an important step in diagnosing fuel pump issues. Here is a detailed guide on how to do it:
Firstly, ensure there is actually gas in the tank. While this may seem obvious, it is an important first step. Don't rely solely on the fuel gauge, as it could be faulty. Add at least two gallons of fuel to the tank and try starting the car. If the car starts, the issue could be a faulty fuel gauge or a failed fuel sending unit.
If the car still doesn't start, the next step is to verify that the fuel pump is working. Ask an assistant to turn the ignition switch to "On". You should listen for a two-second whir, hum, or series of rapid clicks, which indicates that the fuel pump is pressurizing the fuel line to the engine. If there is no noise, this could be due to a lack of power or a failed fuel pump.
Now, check the fuel pump fuse and relay. Refer to your owner's manual to locate the fuse box, then find the fuse corresponding to the fuel pump. Inspect the fuse for signs of failure, such as a break or burn marks. If the fuse appears intact, check the other fuses related to the fuel system and replace any blown fuses. If no fuses are blown, listen for the fuel pump relay clicking when the ignition key is turned.
If the fuel pump appears to be functioning but you still suspect low fuel pressure, you can use a fuel pressure tester. These testers consist of a gauge attached to a fuel hose with multiple fittings, allowing connection to the fuel system of most vehicles. Connect the tester to the fuel system and pressurize the system. The tester will display the pressure in psi, which you can compare to the specifications for your engine. Good fuel pressure depends on the engine—older throttle-body injected systems may need as little as 10 psi, while multi-port injection systems can require up to 60 psi.
Additionally, you can check the fuel pressure regulator, which is responsible for separating the vacuum side from the fuel side. One method is to blow on the vacuum inlet—if no air leaks through, the regulator may still be functioning properly. Alternatively, you can use a fuel pressure gauge to check the fuel pressure at idle and then pull the vacuum line to check the pressure change.
By following these steps, you can effectively check the fuel pressure and diagnose any potential issues with the fuel pump or fuel system.
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Frequently asked questions
The official way to test a pump is to attach a pressure gauge to one side and a vacuum gauge to the other. You can also check the fuel pump fuse, which is often the cause of the pump not functioning. Locate the fuse box, find the fuse for the fuel pump, and inspect it for signs of failure. If the fuse is intact, check the rest of the fuses related to the fuel system and replace any blown fuses.
Have a helper turn the key while you listen for the fuel pump relay clicking. If the relay directly powers the pump, you can try swapping it out. If that doesn't work, use a test light to check the terminals. With the key on and the test light clip connected to the negative battery terminal, you should find two hot terminals.
You can use a fuel pressure gauge, which can be purchased at most auto parts stores. Hook it up to the fuel pump test point and have an assistant rev the engine. If the needle doesn't move, the fuel pump may be faulty.
