The Fuel Supply Components of the Electronic Fuel-Injection System

17-01 Explore the fuel system supply side and determine the correct diagnostic procedures.

The fuel-injection system is something that must be supplied with the proper amount of fuel for it to operate correctly. The supply components include the fuel pump, fuel tank sending unit, fuel tank, fuel filter, fuel pump control module, and fuel pressure regulator. All these components work together to maintain the proper fuel pressure to the fuel injectors so that they can operate correctly. One failure in the fuel supply system can have a detrimental effect on the rest of the fuel-injection system’s ability to maintain operational efficiency.

Fuel Tank

The fuel tank is a simple component whose sole purpose is to hold fuel and contain the fumes that are created by the fuel (FIGURE 17-1). The fuel tank is made of metal or from high-density polyethylene (HDPE) plastic. The metal fuel tanks are stamped out in a simple shape and then welded at the seams to create a fluid tight seal (FIGURE 17-2). The rigidity of steel makes these types of fuel tanks very durable, but it also is a limiting factor, because metal can be bent and welded in only a small variety of configurations. Until recently, these types of fuel tanks were in every vehicle. The HDPE fuel tanks are a blow-molded product that can be designed to conform to the tight tolerances of a modern vehicle (FIGURE 17-3). Unlike a metal-formed tank, the polyethylene resists punctures and other forms of tank destructive events, creating a more resilient component. The ability to conform to the design of the vehicle allows for a more compact package, which decreases wasted space and increases fuel tank capacity.

FIGURE 17-1 The fuel tank on a vehicle is used to hold the fuel necessary to operate the engine. Along with providing fuel storage, it is used to capture the fumes that the fuel gives off as it sits in the tank.

FIGURE 17-2 The metal fuel tank has been used for a long time in the automotive industry. Because it is very durable and relatively inexpensive to produce, it is the go-to type for most vehicles. The drawbacks to using a metal fuel tank are that it lacks the ability to conform to tight areas and that it has a tendency to tear when exposed to sharp objects.

FIGURE 17-3 An HDPE fuel tank is used in applications where the manufacturer wants to use the most available space underneath the vehicle. These types of fuel tanks are resistant to deformation, which makes them a highly used type of fuel containment device.

The fuel tank is a crucial part of the fuel supply system because it holds all of the fuel; it acts as a fume container to minimize the impact of hydrocarbon release into the atmosphere; and it holds the fuel pump and fuel pump sender. Keeping the fuel away from the heat source of the engine and hot exhaust maintains the density of the fuel so that when it is introduced into the engine, it helps to cool the combustion chamber, which will increase the efficiency of the event. Isolating the fuel tank farther away from the vehicle occupants also minimizes the possible risk of a fuel-related issue.

Fuel Pump Relay

To turn the fuel pump on and off, the powertrain control module (PCM) incorporates a fuel pump relay (FIGURE 17-4). Like any electrical component, the initialization of the fuel pump causes it to draw amps—specifically 15–19 amps, which could blow a transistor inside the PCM because it is not a high-amperage circuit. Using the PCM to control fuel pump operation can turn on the fuel pump when the engine is cranking and then turn it off when it is not. Allowing the fuel pump to run when the pressure is not being used can cause the pump to fail sooner and thus need to be replaced sooner than it should have been. On most vehicles, when the ignition switch is turned to run, the fuel pump primes the fuel system with a two-second pulse so that when the switch is turned to start, the engine will not need to crank for long before the fuel reaches the fuel injector, decreasing the start time.

FIGURE 17-4 The fuel pump relay is just like other relays: It is controlled by the PCM and the ignition switch.

Like any electrical circuit, the relay needs two power feeds: One is a battery positive, which is live all of the time, and the other is a switched power that is controlled by the ignition switch or PCM. In some applications, the ignition switch signals the PCM to allow the fuel pump relay to have power. One of the other wires is a switched wire that is controlled by the PCM. The PCM grounds the coil in the relay to allow it to close the switch and connect the battery power to the fuel pump wire to start the fuel pump (FIGURE 17-5). Controlling a high-current component with a low current coil allows for minimizing of a voltage spike that could damage the PCM. This control of the fuel pump relay by the PCM allows other modules to affect the operation of the fuel pump. When diagnosing the relay, do not assume that the PCM is the cause of the issue, because something could be causing the PCM to not actuate the fuel pump relay.

FIGURE 17-5 By using a wiring diagram, the technician can determine which wire is not performing as desired, and then they can start their diagnostic procedures.

Fuel Pump Modulation

As general automotive technology has progressed, the ability to control the operation of the fuel pump has also progressed. Fuel pumps controlled by pulse-width modulation (PWM) are used to control the output of the fuel pump and to extend the life of the fuel pump (FIGURE 17-6). In a PWM fuel system, the PCM controls the on time of the fuel pump by cycling the power feed to the fuel pump. By using the fuel pressure sensor on the fuel rail, the PCM can determine what amount of fuel is being used, how much fuel will be needed, and whether there is a faulty fuel pump. This precise control of the fuel pump allows for ramping up or down based on the needs of the engine, which can create less of a load on the electrical system, thus extending the life of the systems. To accomplish this, the fuel pump relay is eliminated and replaced with a fuel pump driver control module that is also on the network in the vehicle (FIGURE 17-7). This module has the ability to control the operation of the fuel pump based on the needs of the PCM. By using data lines, it is able to monitor other systems on the network to make sure fuel is enabled.

FIGURE 17-6 The fuel pump control module pulse-width modulates the power to the fuel pump, which increases the life of the fuel pump and allows for more precise control of the fuel pressure in the system.

FIGURE 17-7 The fuel pump driver control module is being put on the network so that it can be controlled by the PCM to maintain the fuel pressure when needed and to increase or decrease it so that the engine runs as efficiently as possible. By pulse-width–modulating the fuel pump, the longevity of the fuel pump increases, which makes it last longer in the vehicle before it fails.

Fuel Pump

The fuel pump creates the pressure necessary to operate the fuel-injection system. The pump operates off of the same 12-volt system that the rest of the vehicle runs on (FIGURE 17-8). To help ensure a quicker engine startup, most fuel pumps have a check valve integrated into the pump. This check valve keeps the fuel system under pressure for a period of time after engine shutdown. Over time, this valve will wear out, causing increased cranking times, which means the fuel pump module will need to be replaced.

FIGURE 17-8 The fuel pump operates off of the same 12-volt system as the rest of the vehicle, which must be maintained so that the fuel pump will operate correctly.

Various types of pumps can be used to generate this pressure. A roller cell fuel pump is a positive displacement pump that uses an offset disc with rollers inside a steel ring. This positive displacement pump needs to use a muffler to smooth out fuel flow to the fuel injector. These rollers create enough space to allow fuel to enter the pump to be compressed before it exits the pump (FIGURE 17-9). A second type is a gerotor pump that is similar to a gerotor oil pump, it has an offset ring that moves around the center shaft, which allows it to compress the fuel in the pump. This design creates pulsations in the fuel, so a muffler must be used to smooth out the fluid flow (FIGURE 17-10). The gerotor is a positive displacement pump also. The third type is the turbine-style pump, a non-positive displacement pump (FIGURE 17-11). This pump has an impeller on the end of the pump that pushes the fuel through the pump into the fuel lines toward the engine. Because this is not a positive displacement pump, it does not produce a pulsation, which eliminates the need of a diffuser to muffle the fluid flow.

FIGURE 17-9 The roller cell fuel pump is a positive displacement pump that creates a consistent fuel flow, but it must be used with a muffler because it pulsates the fuel and may cause a running issue.

FIGURE 17-10 The gerotor type of fuel pump uses an offset rotor to create the pressure necessary to operate the fuel system. This is a positive displacement pump.

FIGURE 17-11 The turbine fuel pump runs at very high rpm, around 7,000 rpm, and uses an impeller to generate pressure in the fuel system. These pumps are not positive displacement, so they do not need a muffler, because they do not produce a pulsating fuel flow.

Filter Sock

The filter sock attaches directly to the bottom of the fuel pump (FIGURE 17-12). The fuel sock is the first line of defense of the fuel system against dirt and debris. The fuel that is in the fuel tank has traveled a long way to get to the gas station, which means that through the fuel’s journey, it has picked up material from the different containers that it has been transferred in. From the cracking at the refinery, to the pipeline it flowed through, to the fuel tanker that delivered the fuel to the gas station and then from the underground fuel tanks to the vehicle, the fuel could potentially pick up anything: water, rocks, leaves, or rust. The fuel sock will help to protect the fuel pump before it moves the fuel to the fuel lines and to the in-line fuel filter, before the fuel reaches the fuel injectors. This sock must be replaced any time the fuel pump is replaced, because it gets dirty just like any other filter.

FIGURE 17-12 The filter sock is very inexpensive protection against debris entering the expensive fuel pump. Without this filter sock, debris could damage the pump or the fuel injectors if it makes it that far.

SKILL DRILL 17-1Testing Fuel Pressure

1. When conducting a fuel pressure test, look up the specifications for the vehicle being tested.

   

2. After the specification has been found, find a tap point to attach a fuel gauge to the fuel system. Most systems have a Schrader valve that allows a fuel gauge to be attached quickly and easily. Note: Do not try to attach a fuel gauge to the high-pressure side of a gasoline direct-injection (GDI) engine. The pressures can exceed 5,000 psi (345 bar), which can cause injuries and tool failures.

   

3. Remove the Schrader valve cap, and attach the fuel gauge to the service port, being careful to clean up any spilled fuel so that a fire will not result.

   

4. Once the gauge has been hooked up properly, cycle the ignition key to the run position. When this happens, the fuel pump with run for approximately two seconds, to prime the circuit. Look for any leaks and visually monitor the reading on the gauge. Document the reading, and compare it to the vehicle specifications.

   

5. Start the vehicle up and let it idle. Take another reading, and compare it to the service information to determine whether the fuel pump is putting out enough pressure. Shut the vehicle down.

   

6. After comparing the readings captured from the vehicle, disconnect the fuel gauge from the vehicle and reinstall the Schrader valve cap.

   

Fuel Pump Module

Fuel pump modules are assemblies that provide a base for holding different components in the fuel tank (FIGURE 17-13). This multi-function component is usually made out of plastic or steel so that it has a lot of ridges and can endure the vibration of the normal operation of a vehicle. Incorporating the fuel level, fuel pump, fuel tank pressure (FTP) sensor, and associated wiring, this piece is the backbone of the fuel pump in the fuel tank. The fuel level sending unit, located on the fuel pump module, is a simple variable resistor with a movable arm attached to a piece of foam (FIGURE 17-14). This piece of foam floats on the level of the fuel in the tank, which moves the lever on the resistor to change the resistance of the fuel level circuit. The PCM and the instrument panel cluster (IPC) interpret this resistance by factoring in the design of those components to determine how much fuel is in the fuel tank. In some situations, the level sensor supplies this information only to the PCM, which then uses network data lines to interpret and send the information to the fuel level gauge.

FIGURE 17-13 The fuel pump module holds a variety of pieces that are necessary to the operation of the engine. Including the fuel tank level and the emission system, the sending unit holds vital components needed to monitor the fuel in the vehicle’s fuel tank.

FIGURE 17-14 The fuel level sensor uses varying resistance to determine the level in the fuel tank. The PCM can use this generated resistance to calculate the amount of fuel that is currently available to use in the engine. Along with the fuel level, the PCM can determine the rate at which the fuel is being used, to calculate fuel efficiency.

The FTP sensor is part of the EVAP (evaporative emissions) system and monitors the vacuum created in the fuel tank when the EVAP monitor is active. This is a 5-Vref (voltage reference) sensor that is supplied 5 V, but then as the pressure changes in the fuel tank, the output is different from the 5 V. This sensor can be replaced separately from the fuel pump module.

The main purpose of the fuel pump module is to hold the fuel pump. Mounting of the fuel pump in the fuel tank allows the pump to be submersed in fuel so that it will never run dry and so that the fuel can also cool the pump as it is operated. Without the cooling effect of the fuel, the pump would overheat (over time) and fail. Newer systems with PWM modules can now control the operation of the fuel pump with more precision. This precision lengthens the life of the fuel pump and reduces engine performance–related issues.

Fuel Lines

An often overlooked part of the fuel system is the fuel lines that get the fuel from the fuel tank to the engine (FIGURE 17-15). These lines are strategically placed so that they will not be damaged by any road debris or other items as the vehicle is operated down the road. The material that the lines are made out of is steel or petroleum-resistant plastic, which provides them with a long service life before they will need to be serviced. The limits of steel include that they cannot take sharp corners and that they are susceptible to oxidation, which can then create a leak. By using plastic, fuel lines can conform the line to the area of the vehicle, which can create a better fit on the vehicle. The ability of the plastic line to flex and move helps with decreasing the chances of the line failing. If those plastic lines do fail, repair kit can be used so that the whole line does not need to be replaced when only a portion fails.

FIGURE 17-15 The fuel lines are tucked behind the frame rails and put behind components on the vehicle.

Fuel Filter

The fuel filter is used to limit the amount of contamination that makes it to the fuel injectors (FIGURE 17-16). Just like the air filter or the oil filter, the fuel filter is used to keep the components of the fuel-injection system free from debris so that they operate correctly. Along with removing the debris from the fuel, the fuel filter separates water from the fuel to allow for a more consistent burn and more consistent power generation, as a result of the increased pressures in the combustion chamber. There are two types of fuel filters: replaceable and non-replaceable. The replaceable type have been used ever since the days of carburetion, because keeping the clean fuel available for combustion helps to maintain an efficient process. As with most regular maintenance on a vehicle, a majority of people do not keep up with it, so a lifetime filter was developed (FIGURE 17-17). The lifetime filter became part of the fuel sender so that when the sender is replaced, a new filter would be replaced simultaneously. The purpose of this filter is to stop debris and water in the tank so that it can be trapped inside the fuel tank, never to reach the engine.

FIGURE 17-16 The fuel filter protects the fragile components of the fuel-injection system, which will stop any big pieces of debris before they hit the components of the system.

FIGURE 17-17 The lifetime fuel filter is usually attached to the fuel sending unit so that when the fuel pump is replaced, the filter also gets replaced.

SKILL DRILL 17-2Replacing a Fuel Filter

1. Determine why the fuel filter is being replaced: It may meet the maintenance timeframe, or the customer may be diagnosing a drivability or engine performance issue on their own.

   

2. After determining that the fuel filter will need to be changed, look up the procedure (in service information) on how to replace the fuel filter. Some of these filters are serviceable, and some are not, so thoroughly investigate the system to determine serviceability.

   

3. Clearing the fuel from the lines will minimize the amount fuel that is spilled once the fuel lines have been removed. To do this, remove the fuel pump relay or fuse, and run the engine. When the engine dies on its own, it has used up any residual fuel in the lines.

   

4. After finding the repair procedure, mount the vehicle on a lift, and lift the vehicle.

   

5. Locate the fuel filter and determine whether any skid plates, covers, or other items need to be removed to access the fuel filter.

   

6. The fuel filter is now accessible, so disconnect the fuel lines so that the fuel filter can be replaced with a new unit.

   

7. After the new fuel filter has been installed, lower the vehicle, replace the fuel pump relay, and start the vehicle.