Fuel System Assembly : The Definitive Guide
In-tank fuel pumps usually come with several support components to make a module; this is referred to as a fuel pump assembly. This guide discusses the fuel pump assembly in detail and helps you to understand it better.
Internal combustion engines rely on liquid fuel to run. For the fuel to reach the engine, it has to be pumped from the gas tank. This is done by the fuel pump, which is one of the major fuel system components. A fuel pump can be in-line or in-tank. In-line fuel pumps are either electrical or mechanical. These pumps usually install along a high pressure line to feed the fuel injection system with a continuous flow of fuel. A separate low pressure return line takes excess fuel back to the gas tank.
You will learn about what a fuel pump assembly is, the parts that make it, how to fix it, and the procedure to replace the one in your car. The final chapter offers advice on how to buy a quality fuel pump assembly for optimal engine performance. Read on.
Table of Contents
What Is A Fuel Pump
A fuel pump assembly is the unit in a gas tank that sends fuel to the engine. Other than the pump itself, the assembly comprises several other components, each with a special function in the fuel pumping system. Also known as fuel pump module assembly, the fuel pump assembly ensures that clean, pressurized fuel reaches the fuel injectors.
Fuel pump assemblies are usually located in the gas tank, submerged in the fuel. The main pumping component in the assembly is an electric motor that spins at high speed to an impeller, several valves, and a pressure regulator. How does an auto fuel pump differ from the fuel pump assembly?
Fuel Pump Assembly Vs. Fuel Pump
An automotive fuel pump is usually a stand-alone device that consists of a motor and pumping section. It can be installed in the gas tank or on the fuel line. A fuel pump can also be electrical or mechanical. Older carbureted fuel systems use mechanical fuel pumps, while modern direct injection engines use electrical fuel pumps.
An automotive electric fuel pump is usually a canister shape with an inlet, outlet, and electrical connections. Unlike the electrical fuel pump that pushes fuel at high pressures, a mechanical fuel pump operates at low pressures and the reason why they suit carburetor systems.
The fuel pump assembly, on the other hand, is more of a composite unit. It houses the vehicle’s fuel pump alongside other parts. In most modern vehicles, the unit also contains the main fuel filter. The assembly is usually placed in the fuel tank where it pulls fuel and sends it into the fuel lines at high pressure.
A fuel pump assembly sits in the gas tank, submerged in the fuel. The gas tank and fuel pump assembly joint at the point of installation using screws for an airtight seal. This ensures no air enters the fuel pump and tank assembly and prevents an explosion.
Fuel Pump Assembly Diagram
A complete fuel pump assembly comprises many different parts, but the main ones include a screen filter, motor, and pump. Here is a look at these components in detail.
The screen filter
Not to be confused with the fuel filter, the filter screen in a fuel pump assembly is a simple strainer. It is a mesh sieve, whose main function is to trap bigger debris. While a fuel filter can catch particles smaller than 10 microns, the strainer screen in the fuel pump assembly filters contaminants that are as big as 70 microns.
The sock filter sits at the bottom attached to the inlet opening, or the part that pulls fuel into the motor. Because it does not filter fine impurities, this mesh strainer can last a long time. Only fuel with excessive amounts of contaminants would cause it to clog too soon.
Some fuel pump assemblies also include a main filter alongside the sieve filter. Housed in the module, the two filters work together to ensure the fuel that is pumped from the gas tank is clean and ready to be delivered to the engine.
The Fuel Pump
Of all the fuel pump assembly parts, the pump is what forms the heart of the unit. It consists of a small DC motor, an impeller to push fuel, and the components that enable the pumping action. Fuel pump motors can be pusher or puller types. Generally, the types used in the in-tank fuel pumps are the puller type.
Although not efficient at extracting fuel from the tank, theses motors can push fuel at great pressures. This is desirable in modern fuel injection systems where pressures as high as above 40 psi are needed. Because these motors run at high speeds, being immersed in fuel helps to cool and lubricate the moving parts. It also helps to dampen the noise produced.
The Fuel Pressure Regulator
As the name implies, this is the part that regulates fuel pressure. Accurate and consistent pressure is required at the fuel injection system, or the engine will run too lean or too rich. Both scenarios are not desirable in the fuel delivery system. They can result in loss of power, inefficient combustion, or even damage.
The fuel pump pressure regulator is essentially a valve that consists a spring and diaphragm. When pressure is too high, the valve opens to let excess fuel flow back into the gas tank. Older carburetor engines have the regulator outside of the fuel tank, towards the end of the injector rail. In modern direct fuel-injected systems, the fuel regulator is built into the pump assembly.
Some pressure regulators, especially, inline fuel pressure regulators, can be adjustable. An adjustable fuel pressure regulator allows one to increase or decrease the maximum allowable pressure. Some come with a pressure gauge and offer more options.
An adjustable fuel pressure regulator with gauge lets you control pressure to precise levels. This is usually a return style fuel pressure regulator that mounts in the pressure side of continuous fuel lines. A universal fuel pressure regulator fits a wide range of vehicles, which makes it one of the most used types of external fuel pressure regulating units.
Regardless of whether it is a gasoline or diesel fuel pressure regulator, this part of the fuel system is one of the most useful. Too little fuel pressure and the engine runs too lean. Too high pressure and the engine runs too rich. Although rare, the regulator can break down and cause reduced fuel pressure. It can also get stuck, causing the pump to run at maximum pressure.
How Does the Automotive Fuel Pump Assembly Work?
As we have seen, the assembly consists of a fuel strainer, a pump, and a pressure regulator among other components. When the vehicle is switched on, the fuel pump, through the connectors, receives an electric excitation. This causes it to start pulling the fuel in the tank into the assembly.
The sieve strainer screens out impurities as the fuel gets pulled through it by catching the larger debris. From the strainer, the fuel flows into the fuel pump, which is essentially a DC motor and pumping components. Here, the fuel is swirled through openings to produce the required pressure. Some fuel pump assemblies will have a fuel filter inside them.
A pressure regulator controls the amount of fuel that gets pumped through the fuel line. The fuel pump regulator opens and closes as required, using a spring to enable that. There is also the fuel sending unit. It consists of a fuel sensor that sends a signal to light the dashboard light, and float that controls the fuel level gauge.
How to Fix a Fuel Pump Assembly
A fuel pump assembly rarely goes bad. But when it does, the results can be drastic. Because the assembly feeds the engine with fuel, its failure can be felt at the engine. It may start sending inadequate fuel to the injection system, resulting in poor engine performance and loss of power. In the worst of scenarios, the fuel pump assembly may stop pumping fuel altogether, causing the engine to stop running or fail to start.
A bad fuel pump assembly may also give false fuel level readings, causing one to run on an empty gas tank. This can be damaging to the fuel filter and the fuel pump itself. How can you tell that a fuel pump assembly is failing?
Signs that a Fuel Pump Assembly is Failing
Engine issues can be caused by the failure of a range of components. However, a bad fuel pump assembly is one of the most common reasons for poor engine performance or even damage. A faulty fuel pump assembly will cause these symptoms.
Low Gas Mileage– if you find yourself having to refill the gas tank many times than usual, it could be because the fuel pump assembly is not working correctly. A damaged return valve causes fuel to pump at maximum pressure. The engine then receives more fuel than is necessary. Because excess fuel in the engine does not get stored, it results in low gas mileage.
Hard Starting– when the fuel pump is failing, it cannot build up enough pressure in the fuel system to start the vehicle. You have to try a few times before the engine can crank up. This happens as the engine tries to attain the pressure and the amount of fuel necessary to start.
Whining Fuel Tank Noise– the fuel pump assembly contains a DC motor. Normally, the motor produces a low humming sound. This changes when the assembly is damaged. The noise level increases and becomes a whine. This noise should not be confused with the audible sound that most fuel pumps produce during the first few seconds. A worn motor remains noisy throughout.
No Sound– a dead fuel pump will not produce any sound. Because it is housed in the fuel pump assembly, its failure means the other parts of the assembly not working. And if working, the components may not be useful anymore. The whole assembly would then need to be taken out, repaired, or replaced with a new one.
Loss of Engine Power– this happens when the engine is under stress, such as when accelerating, driving up a hill, or if carrying a heavy load. The damaged fuel pump cannot send enough fuel to the engine, and the engine struggles to cope.
Sudden and Erratic Power Surges– a faulty fuel pump assembly cannot maintain constant fuel pressure. At one time, it is delivering low amounts of fuel. In another, the pressure will increase on its own. It causes a power surge, something like you depressed the gas pedal.
Engine Not Starting– when damage is so severe as to cause total failure of the fuel pump assembly, the vehicle may not start at all. A failed fuel pump cuts off the fuel supply to the injection system and putting the starter on will not bring the engine to life.
Fuel Pump Assembly Repair
Once you notice these symptoms in a vehicle, you may want to fix the fuel pump assembly. Before deciding to fix the pump, it is advisable to carry out a fuel pump assembly diagnosis. This would help to confirm the problem and find out what parts of the assembly are faulty. Fuel pump assembly failure can be caused by a worn or burnt out pump motor, clogged filter, or bad electrical connections.
How to Diagnose a Fuel Pump Assembly
Because faulty fuel pump components often cause pressure and electrical problems, diagnostic procedures normal involve measuring pressure and electrical connection voltages.
Checking the Fuel Pump Fuse– a fuel pump assembly can fail if power does not reach the electrical components such as the motor, fuel sensor, and others. To check if it is a power failure, start by inspecting the fuse box. You can find its location by consulting the car’s manual and finding the fuse that is related to the fuel pump. Check to see if the fuse is blown. If the fuel pump fuse is intact, check the other fuel system fuses.
Checking the Fuel Pump Voltage– you may have a functioning fuse, but no power at the fuel pump. Check the circuit going to the pump. Test the fuel pump relay, too, if it is faulty.
Performing the Voltage Drop Test– using a voltmeter, measure the voltage of the fuel pump assembly wires. The power cables should show full voltage and the ground wires proper ground. Any slight volt difference could be a sign of bad connections, perhaps corroded contacts.
Fuel Pressure Test– after conducting tests for electrical failure, the next check should target the working of the fuel pump. If there is a problem in the operation of the motor or the various valves, it should cause pressure differences, either high or low. You will need a fuel pressure gauge, which you can easily obtain from an auto parts shop.
To test for pressure, attach the pressure gauge to the pressure testing point. In the carburetor fuel systems, the point is usually located at the injector rail. Modern vehicles that use direct injector systems do not have this fitting. To perform the pressure test, you may have to detach the fuel filter from the fuel line so you can attach your pressure gauge. Only remember to release the pressure in the line as well as excess fuel.
By having someone rev the engine while you observe the pressure gauge, you can determine if the pump is working correctly. A needle that remains stationary or only moves a little indicates a problem with the pump. But low pressure could also result from a clogged filter. To determine the problem, rule out a bad fuel pump filter screen.
Checking the Fuel Pump Filter Screen– sometimes, the problem can be the filter at the intake of the fuel pump assembly. If the fuel has been generally unclean, the sieve might be blocked to produce low pressures in the fuel lines. Checking the filter would require you to remove the fuel pump assembly from the gas tank. But that would also allow you to fix the faults in other components.
Fixing the Fuel Pump Assembly
Replace a blown fuse. If the problem is corroded or broken connections, replace them. Mechanical failure in the fuel pump assembly can also be repaired as well as a clogged filter. That is because the various parts can be sold separately. For an in-depth description about how to do it, check the next chapter.
How to Rebuild a Fuel Pump Assembly
Because a fuel pump assembly consists of independent parts, it can be rebuilt to replace faulty components. Doing so is less costly than having to purchase a replacement. When only one or two components are faulty, having to throw away the whole assembly is not what many car owners would want to do.
Rebuilding a fuel pump assembly requires you to remove the unit from the gas tank. You also need the fuel pump assembly rebuild kit or the parts you intend to replace with you. Some knowledge about the working of the assembly, too. If you do not, the rebuild kits come complete with the instructions to carry out the process.
The Process to Rebuild a Fuel Pump Assembly
It starts with getting the assembly from the gas tank, taking the components apart, assembling the unit with the new parts, and ends with installing the rebuilt assembly back in the tank.
Things you will need:
Wrenches, screwdrivers, rags, protective gear, and the fuel filter assembly kit or parts
Caution: work in a place that is well ventilated and away from sparks that would ignite fuel vapor.
Removing the Fuel pump Assembly From the Gas Tank
Locate the fuel tank. It is usually mounted under the back seat. Using a wrench, unfasten the seat and remove the cushion. When removing the fuel pump assembly, fuel may spill around. Protect the surfaces by lay a cover all around the work area, such as a rubber mat.
Disconnect and clamp the negative terminal of the battery. Fuel, especially gasoline, is highly flammable and could be a safety risk when you remove the fuel pump assembly. Disconnect the vacuum and breather hoses, too.
Remove the screws that hold the fuel pump assembly to the fuel tank and detach the ring that had the screws.
Slowly pull out the fuel pump assembly. To prevent dirt and debris from entering the gas tank, cover the opening that is left after removing the assembly.
Disassembling the Fuel Pump Assembly
Detach the fuel level sending unit by pulling out the connectors. It is as simple as pressing latches that hold the connectors in place. Place the sender aside on a safe surface.
Using a screwdriver, remove the filter by lifting the lid gently, and pulling at the filter. Detach all the latches until the filter is free from the assembly.
The next part shows you how to remove fuel pump from the assembly.
Use a screwdriver to lift the lid on top. Do the same to the rubber boot at the other end. Now, pull out the pump from the fuel pump housing. You may need to turn the pump to wiggle it out of the housing due to the tight fit.
Inside the filter housing is the fuel pressure regulator. Simply pull it out. Keep the regulator in a clean place. It contains sensitive components that may be blocked by debris.
Assembling the Fuel Pump Unit With the New Parts
With the main components disassembled, we can now replace them with the new parts. Unless the old sock filter is severely clogged to affect the suction of fuel, it is advisable to use the older one. That is because new filters tend to affect the function of the float, resulting in false fuel gauge readings. This may cause you to run a gas tank that is almost empty unknowingly.
If you have to use a new filter, start the assembly process by attaching it to the fuel pump assembly. Here are the steps to follow.
Fit the sock filter into the inlet point on the assembly and press it in. Clip it into place.
Next, install the new pump. Use the old nozzle spacer, but a new O-ring. The O-ring must provide a tight seal to prevent leaks. Therefore, ensure the one you use is similar to the old one.
Attach the wiring harness to the new pump. If the harness is broken or damaged in any way, replace it with a new one.
Slide the new fuel pump into its housing, ensuring no part gets displaced in the process. Replace the rubber boot that attaches to the bottom of the pump.
Replace the spout and the pump support.
Next, replace the fuel pressure regulator by installing its O-ring and inserting it in the filter housing.
Assemble the head by replacing the terminal lug, installing the O-ring, and inserting the filter. Finish the process by installing the fuel level sending unit and replacing the various connectors.
Your fuel pump assembly is now ready to be installed in the gas tank for testing and troubleshooting purposes. Before we can replace every part, we need to be sure that we have done everything correctly and that the assembly is operational. In the next chapter, we carry out the tests to determine if the assembly is working.
Fuel Pump Replacement
Whether a rebuilt or new fuel pump assembly, knowing how to install and test the new unit is essential. It can save you a lot of professional service expenses. If you are a DIY enthusiast, here is the process to place a fuel assembly into the gas tank, troubleshoot it for issues, and do all that is necessary to ensure a proper installation.
Installing the Assembly in the Gas Tank
Here are the steps to follow. The procedure applies to the typical fuel pump assemblies used in most modern vehicles. As mentioned earlier, ensure you work in a ventilated area and away from spark and flames. That is because the fuel in the gas tank may produce ignitable vapor.
Lower the assembly into the tank and replace the ring and the screws. The installation is the opposite of the removal process.
Prepare the installation for testing by replacing the hoses and connectors. These components do not need any sealing. They fit closely, and you only need to attach the hoses to the right nipples, and the electrical connectors to their sockets.
Replace the battery’s negative terminal that you had disconnected earlier.
Testing and Troubleshooting the Assembly for Issues
Turn on the ignition. The fuel pump should produce some sound as of tries to build up pressure in the fuel lines. After that, the noise level should drop since the pump should not be working as hard. If it still makes noise, there could be a problem. Check the electrical connections and ensure they are correctly fitted. Although a new fuel pump is unlikely to be faulty, it can be so if the test to check it indicates a problem.
Next, start the engine and observe how it responds. If it starts, the fuel pump installation is sound. If it fails to start or idles roughly, you may need to troubleshoot the fuel pump assembly. Use a pressure gauge to do so. It will help you rule out fuel pump defects which would be one of the reasons for low pressure in the fuel limes.
Observe the fuel gauge needle when the engine is started. Low pressure can indicate various problems with the fuel pump assembly. It could be a faulty fuel pressure regulator that is limiting the flow of fuel, or it could be the nozzle O-ring that is leaking. A leak at the O-ring of the feed spout could also be the reason for low pressure. Check the parts before completing the fuel pump assembly installation process.
If the installation is working correctly, it is time to finish connecting every part. Attach to every remaining component to the assembly. Since this is almost the final step, it is advisable to ensure nothing remains behind, and that everything mounts where it should be.
Finish installing the rebuilt fuel pump assembly
Replace the seat and the seat cushion.
Test the installation for one last time to confirm that it is functional.
Reasons for a Damaged Fuel Pump Assembly
span style=”font-family: ‘trebuchet ms’, geneva, sans-serif; font-size: 14pt;”>Apart from age, there are reasons why a fuel pump assembly components would wear down rapidly. Sometimes even to become damaged. Knowing what these causes of wear or damage can help you to take care of the assembly better and minimize instances where you undergo unexpected expenses. The causes of fault in a fuel pump assembly include.
Bad driving conditions– excess moisture can condensate in the fuel tank and lead to corrosion. Moist conditions could also result in rust which would clog the filter at the intake. Within no time, the fuel pump may experience operational problems.
Driving on an almost empty gas tank– the fuel pump operates while submerged in water. That helps to ensure proper suction. When the fuel level is low, the pump works harder to pull fuel up the unit. If this happens for extended periods, the pump would wear too quickly and become weak. Low fuel also results in sediments being pulled by the pump, causing the filter to clog.
Dirty fuel– using fuel that contains too many impurities can take a toll on the fuel pump assembly. In addition to wearing the motor and pump, the contaminants clog the filter and reduce the pressure in the fuel lines. In the long run, the engine’s performance inevitably drops.
Bad connectors– the fuel pump assembly uses an electric pump and several other electrical components. That means wires will run from various circuits into the assembly. If one if these connectors become corroded, it can mean a malfunctioning assembly. The most affected component is often the fuel pump. Without adequate power, it cannot pump fuel in the right amount or pressure, and the engine does not run as required.
For a fuel pump assembly to last a long time, it is essential to avoid things that cause it to wear or become damaged. However, you will eventually need to replace the assembly. This can be after many years, though. When that time comes, you want a product that will assure you of proper function as well as durability. How do you obtain the right assembly for your type of vehicle? The next part of this fuel pump assembly helps you to do that.
How to Buy a Fuel Pump Assembly
Fuel pump assemblies are costly vehicle parts, and you may not want to make a mistake when buying one. To get the right assembly for your vehicle, there are several factors to consider. These range from fuel pump assembly cost, quality, to compatibility. We compiled this short but detailed buying guide to help you in that direction. It answers the questions you might have when shopping for a fuel pump assembly.
Factors When Buying a Fuel Pump Assembly
Among the things to consider include:
This should be the first step of the process to purchase a fuel pump assembly. Vehicles are different, which means one fuel pump assembly may not fit another. Before choosing the type and model to buy, consider the year your car was manufacturers, its type, model, and various other things. It will save you the troubles of having a fuel pump assembly you cannot use. If buying online, narrow down your search by selecting the product according to your vehicle type. When shopping at a physical store, you will still need to choose a compatible unit.
If your car is the older type, it will be a carburetor type that uses a mechanical fuel pump. If that is the case, you do not need the high pressures created by the an electric and in-tank fuel pump assembly. These only suit the direct injection systems where high fuel pressure is necessary. Speaking of pressure, not all fuel pump assemblies come with the same pressure capabilities. The type you choose should suit the requirements of the fuel injector nozzles used by your vehicle. Excessive pressure than the injectors can handle would result in damage.
To ensure proper performance, choose a fuel pump whose flow rate matches the specifications set out by your car’s manufacturer. Choosing the wrong flow rate can mean an underperforming engine or one that produces a lot of emissions. Both instances would affect the operation of your vehicle, both in performance and harm to the environment. To prevent buying the wrong kind of pump, always consult your car’s manual for the various features and specifications.
Fuel pump assemblies are pricey auto parts, with the cost to buy them ranging from a hundred to three hundred US dollars. Add that amount to the charges to hire a mechanic, and pricing becomes one of the considerations to make when buying this auto part. While one can save on the fuel pump assembly replacement cost through a DIY approach, the amount still remains high. However, cost consideration does not mean settling for a cheap fuel pump assembly. It means going for a moderately priced brand and model.
It is common practice by vehicle owners to prefer brands that are known to offer quality products. The idea is to buy a fuel pump assembly that has been tried by many and proved to be quality. Online sources can point you to a trusted manufacturer. Alternatively, you can ask around for recommendations from friends or even relatives. You want a quality fuel pump assembly, and you can only confirm that by using the product yourself or learning about it from others.
Whole Assembly Vs. Rebuild Kit
You may prefer to rebuild the unit than carry out a complete fuel pump assembly replacement. While that may reduce the overall costs, it is good to aware of the upsides and downsides of either option. A rebuild saves you money, but may not last for long. Replacing some older components may also result in operational issues.
For example, even the best fuel pressure regulator will fail eventually. While you can purchase a fuel pressure regulator kit to replace the part if it wears, the additional repair costs can be more expensive in by the long run. For a fuel pump assembly that only one or two parts are faulty, the rebuilding option would make a lot of sense.
Fuel Pump Assembly Frequently Asked Questions
When buying or looking to install a fuel pump assembly, these questions may present.
How much should I pay for a fuel pump assembly?
Fuel pump assembly price varies across brands, types, and models. Expect to part with between $100 to $300.
Why is the flow rate important when buying a fuel pump assembly?
It determines the efficiency of the fuel pump. You do not want to overlook that unless you want to have performance issues with your engine.
Does the type of fuel matter?
Some pumps may not be suitable for some fuel types. Therefore, it is essential that you choose accordingly.
Should I take my car to a mechanic for a fuel pump assembly replacement?
While it is recommended to do so, a DIY route would save you the hassle and expense. Besides, the process to replace a fuel pump assembly is straightforward and doable by almost anyone who knows a thing or two about vehicles.
How long would it take to install a fuel pump assembly?
The length of time to finish the job can vary from one individual to another or across vehicle types. The average timeframe is between 1 and 2 hours.
In the fuel systems of modern vehicles, the fuel pump assembly makes an essential component. It pumps fuel to the injectors, helping to ensure optimum engine performance. As such, a faulty assembly can mean a car that does not start, stalls unexpectedly while running, or loses power when the engine is under stress.
This fuel pump assembly guide unveils this essential auto part, helping you to understand it better. You will be able to take care of the assembly by preventing situations that would cause damage. The guide also provides information regarding fixing a bad fuel pump assembly. And finally, how to buy a replacement.
For more information regarding the auto parts that send fuel to the engine, read the fuel pump guide. It provides an overview of the different kinds of fuel pumps, one of which is found in the fuel pump assembly used by modern vehicles. Not only that, but also everything about the component and its function in the fuel system.