Installing Subaru Stretch Belts

If you see a belt on a late-model Subaru does not have an automatic tensioner and runs between only two or three components, it’s probably a stretch belt. You may also notice some belts will have the words “stretchy” or “stretch” written on the back. These types of belts typically are used to turn the A/C compressor on the 2.5L four-cylinder engine in 2008 and up models.

The stretch belt can help to simplify the serpentine belt system on the Boxer engine. It can also increase the efficiency of the engine by allowing it to run with less tension on the alternator and power steering. Beyond that, it can extend the life of the alternator by reducing the load on the bearings.

Subaru stretch belts can last 100,000 miles or more. On a worn belt, the cracks or damage to the backing of the belt will not be evident to the naked eye. This is why an inspection method measuring groove depth is recommended — you simply cannot go by mileage recommendations alone.


When inspecting a stretch belt, always measure the depths of the groove with an inspection tool because the differences between a worn belt and a good belt can’t be seen or felt. The new materials used to manufacture a stretch belt will not crack or separate like older belts before the grooves are worn. Belt inspection gauges are available from manufacturers and distributors, so check their websites or ask your distributor if you’re in need.

Poor pulley alignment is the No. 1 cause of belt noise and premature wear of stretch belts. If the pulleys have poor alignment, the belt will be worn on the edges and might look frayed.

Alignment problems can stem from issues with shaft endplay in an A/C compressor or crankshaft. Alignment problems can also indicate a worn A/C clutch or a crankshaft pulley/dampener that is about to fail. Also note that leaking seals can contaminate the belt.

Worn Belts

When a stretch belt exceeds wear specifications, it’s no longer able to effectively grip the pulleys and will start slipping. The primary cause of this slippage is when material is removed from the belt’s grooves, rather than it stretching and losing tension.

Over time, small debris and the interaction with the pulleys will wear the shoulders and valleys of the grooves. When the grooves become too shallow, the pulleys bottom out. When this happens, the walls of the groove can no longer grip the pulley and it slips.

If you are removing an old stretch belt from a Subaru, just cut it. Even if the belt is still in excellent shape, the act of pulling the belt over the A/C compressor clutch or crankshaft pulley will damage the inner core.

These belts have a thermo-elastic core designed to keep tension on the pulleys during a long lifecycle. The material acts like shrink tubing for a wiring harness. Once the belt has been run and exposed to the underhood temperature, the heat will decrease the length of the belt and, therefore, properly tension it.

Never use a screwdriver or other sharp object to install the belt because if the belt is cut or the surface or grooves of the pulleys are damaged, the belt will eventually fail. Special tools are available from various tool and belt manufacturers that act as a ramp on the leading edge of the pulley. Some applications will require special tools to hold the belt on the accessory pulley, as is the case for the Subaru A/C compressor pulley.

There are many tool designs, but they all perform the same task of pulling the belt over the leading edge of the crankshaft pulley without damaging the belt. Always follow the directions for proper tool placement and for the correct direction to turn the crankshaft. After the belt is installed, confirm the belt is in the grooves and recheck there are no alignment problems. Run the engine for a few seconds before doing this final check.  

Article courtesy Underhood Service.


Fuel Pump Diagnostics: Using Scan Tools

The most common diagnostic procedures for fuel pumps in the past were analog and hands on. Most fuel pump-related problems could be solved with a pressure gauge and voltmeter. Today, the scan tool is the most important tool when diagnosing a fuel supply problem.

On early vehicles, the fuel pump was energized when the key was turned on and a vacuum-operated diaphragm regulated fuel pressure. Today, input from at least two modules and various sensors that are networked on a high-speed serial data bus is required for a fuel pump to operate. While this may sound like it would complicate the diagnostic process, it actually simplifies diagnostics and can save you from unnecessarily dropping a fuel tank.

With a scan tool, it’s possible to verify if the modules controlling the fuel pump are receiving the correct data like oil pressure, crank position and key ­position. Some late-model imports have even turned the fuel pump into its own module or node on the high-speed serial data bus. The module may share data like the fuel level and tank pressure with the ­instrument cluster module and the ECM.

What this also means is that this data can be monitored with a scan tool. If the serial data bus is unable to communicate with certain modules like the theft deterrent system or even the Body ­Control Module (BCM), it could cause the fuel pump to shut down.

Most late-model vehicles have return-less fuel systems. Instead of using engine vacuum to a pressure regulator under the hood, the system uses engine data and varies the speed of the pump to meet fuel requirements. The pump is energized with pulse-width modulated voltage. This means that if you connect your voltmeter to the fuel pump circuit, the readings will bounce around instead of being a constant voltage.

A scope is required to graph the amperage and voltage. These systems have different modes for start, acceleration, deceleration and fuel cut off. On some vehicles, these modes can be observed on an enhanced or factory scan tool as part of the Mode 6 Data.

Initial Diagnostics

The most common ­customer complaints when it comes to fuel pumps are a no-start condition, intermittent no-start condition or even hard starting. The first step in any diagnostic process is to perform a ­visual inspection of the ­vehicle.

Next, verify the customer’s complaint. Many diagnoses go wrong because the technician fails to verify the customer’s concern. If the customer says it does not run, make sure it will not start and run.

Forget your “noid” lights on most modern vehicles. This low-cost tool worked well on simple vehicles, but with modern vehicles it can lead you down a diagnostic black hole. If the vehicle has Gasoline Direct Injection (GDI), there is no way you could even access the injectors to install a noid light. If you do feel compelled to prove the injectors are pulsing, try using a scope.

Forget the fuel pressure gauge at this point in the diagnostic process. Even if there is pressure at the fuel rail, this information is of little use on newer ­vehicles without having access to the parameters. Some port fuel injection systems and all GDI systems have pressure sensors that can be observed with a scan tool. Also, GDI-equipped Asian and ­European models do not have ports to attach the gauge.

After the visual inspection and verifying the customer’s complaint, it’s time to connect the scan tool. First, pull the codes and make sure the modules are communicating on their communication buses. Some low-end generic tools may not be able to talk to all the modules. This is where an enhanced or factory scan tool comes into its own.

Many enhanced or factory scan tools can perform a “health check” that can pull codes and parameters from the modules on the vehicle with just one press or click. Some scan tools have automated tests that can bi-directionally control components to automatically confirm operation.

With the codes pulled, you can come up with a ­diagnostic strategies and further tests to resolve the no-start condition. Service information is just as ­critical of a tool as a pressure gauge.

Every fuel system has a set of parameters that must be set in order for the pump to be energized. For some systems, this may include a crank sensor signal, oil pressure and maybe a check with the ­vehicle theft deterrent module.

If the vehicle has any “loss of communication” codes like U1000, resolve those problems first before diagnosing or replacing the fuel pump. While these codes may seem like they have nothing to do with the fuel pump, often a dead module or short in the serial bus can result in a no-start condition.

After you’ve performed the checks with your scan tool and have confirmed with the service information that it could be the fuel pump causing the no-start condition, you can carry out the physical tests to confirm the condition of the fuel pump.

GDI Strategies and Scan Tools

Diagnostics fundamentals for GDI are not that much different than conventional fuel injection systems. These systems inject the right amount of fuel directly into the cylinder. These systems are very efficient and are able to get the right amount of fuel into the cylinder so no fuel is wasted by not having to spray on the back of the intake valve.

In fact, after working on a few GDI systems, you may find that they get easier to work on due to the tighter long-term and short-term fuel trim parameters.

GDI makes more horsepower for a given engine size. This is why Mercedes-Benz and BMW have been able to get away from V10 and V12 engines. Utilizing GDI systems, their new V8s are able to make more power while using less fuel.

The diagnostic strategies are similar to port fuel systems, but most of these systems have an additional fuel pump, pressure sensors and a different style of injector.

With the injector in the combustion chamber, the pintle and seat of the fuel injector are under extreme pressures. To overcome the cylinder pressures, the fuel pressure supplier to the injector may be as high as 2,000 psi.

The in-tank pump in GDI systems is more responsible for volume than pressure. Fuel on this side of the system is called the low-pressure side. A fuel pump on the engine pressurizes the fuel for high-pressure injectors. This pump is driven off a lobe on the camshaft. This part of the fuel system is called the high-pressure side.

The pressure from the high-pressure fuel pump is monitored by the Powertrain Control Module (PCM) through a sensor and can be modulated by changing the volume of fuel entering the pump inlet. While specific pressures vary among different vehicle applications, most high-pressure pumps are capable of producing at least 2,000 psi of fuel pressure. These extremely high fuel pressure levels are required to overcome compression and combustion pressures ­inside the cylinder and to inject a relatively large volume of fuel directly into the cylinder in a very short amount of time.

Factory and enhanced scan tools can monitor pressure transducers on the high and low sides of the system. This information can be used to diagnose the health of the low-side and high-side pumps. These tools will have the PID parameters for these components as part of the Mode 6 data. These parameters can tell you what the pressures should be during the different modes of operation. Also, if this data is used in conjunction with the waveforms of the injector pulses, it’s possible to ­perform cylinder balance and other diagnostic tests. The pressure transducers can also be used to monitor system pressures to diagnose hard-start ­problems.

Maintenance and the reduced frequency of ­engine oil changes have been known to take their toll on some GDI high-pressure pumps. For example, some VWs and Audis are experiencing wear on the follower on the pump due to poor lubrication and oil that has broken down. The follower that rides on the camshaft can wear and lose metal at the base.

The pump is very sensitive to the changes in ­dimensions of the follower and it can result in lower fuel pressures. This condition is initially diagnosed with a scan tool and not feeler gauges.

So much of the diagnostic process for fuel pumps can be performed from the driver’s seat of the vehicle with a scan tool. This makes you a more productive technician and the ­diagnosis more accurate. And this translates into a more profitable shop.

Article courtesy Underhood Service.


Valvoline Launches First Hybrid-Specific Motor Oil

A new motor oil for the estimated 5 million hybrid vehicles on the road will be available in 2020 with the new Valvoline Hybrid Vehicle Full Synthetic motor oil.

Valvoline Hybrid synthetic motor oil
Valvoline is releasing a new hybrid vehicle full synthetic motor oil in 2020.

Valvoline Hybrid Vehicle Full Synthetic motor oil will meet the latest industry standards and will be sold in 5W-30 and 0W-20 grades, covering most hybrid models currently in use, including all common hybrid vehicles manufactured by Toyota, Honda and other auto manufacturers. According to the Toyota Motor North America November 2019 sales report, not only have overall hybrid sales increased 65.4% since November 2018, but Toyota division hybrid sales are up 68.4% for the same time period.

“Innovation is in our DNA, so we are constantly striving to develop new products and formulations that meet future consumer demand,” said Heidi Matheys, Valvoline chief marketing officer. “No matter your vehicle type, Valvoline has tested and proven products to help keep it performing at its best for the life of the vehicle.”

Hybrid engines share many similarities with traditional engines, but they also have unique challenges that fluids and lubricants must work to address. These include a hybrid engine’s constant engine start and stop, which can prevent warm up and peak performance. Low engine operating temperatures can create excess water vapor that dissolves into the oil resulting in sludge, corrosion and motor oil breakdown that can negatively impact fuel economy and engine life.

This announcement follows the brand’s recent launch of a product line specifically for electric vehicles.

“Valvoline’s pursuit of new solutions to new problems challenges our unique in-house Valvoline Engine Lab to create flexible formulas that are proven to extend engine life,” said Fran Lockwood, Valvoline chief technology officer. “Valvoline Hybrid Vehicle Full Synthetic motor oil contains a special blend of additives and superior antioxidants to provide the ultimate protection for hybrid engines.”

Automotive Video

VIDEO: Diagnosing Ignition Related Misfires

Is the misfire the fault of the ignition coil, spark plug or could it be the spark plug wires. We’re going to find out how to test and rule out the wires. Sponsored by Blue Streak.

Ignition wires may not be as popular as a decade ago, but there are a lot of wires out there connecting spark plugs to coils and distributor caps.

Since they have to live under the hood, ignition wires are subjected to heat, oil and vibration. They can fail and cause a misfire and code.

Be sure to first visually inspect the wires and engine.

One of the most damaging elements under the hood is vibration. Excessive vibration can loosen the connection at the coil, plug or distributor cap. This can increase the resistance and energy required to fire the spark plug and damage the spark plug. Look at the general condition of the engine and check for issues like vacuum leaks and even excessive carbon deposits. Also, look at how the coils and wires are mounted to the engine.

Heat can burn wire insulation and boots. If the wire or boot is crispy it is more likely to offer the spark an easier path to ground. Look for missing heat shields and spark plug wires that were not properly routed past exhaust manifolds.

Look at the wire to see if there is any damage due to rubbing against other engine parts. Abrasions to the outside of the wire insulation can cause sparks to jump and impacts can crush and damage the wire inside insulation. Make sure to inspect the motor and transmission mounts for excessive movement.

Last, use an ohmmeter with the leads attached to both connectors of the spark plug wire. The resistance for most resistor core wire is between 10,000 to 12,000 ohms-per-foot. However, consult the service information for the correct value.

By performing these easy checks, you can determine if the spark plug wires are the problem or it is another component in the ignition system or on the engine.

Courtesy of Underhood Service.


Alternator Pulley Diagnostics

When faced with an illuminated charge light diagnosis on most late-model vehicles, do not automatically assume the problem is inside the alternator and potentially unserviceable. The problem could be the pulley and belt drive system. Neglecting to test and diagnose the pulley can lead to unnecessary replacement. 

Almost every late-model car or truck is equipped with an overrunning alternator pulley (OAP) or an overrunning alternator decoupler (OAD). An OAP is a one-way clutch like a socket wrench that turns in one direction and locks when turned the other direction. An OAD operates in the same manner but has a special clutch and spring that absorbs vibration to smooth out the vibrations in the drive belt system. Regardless of the type, the pulley should be checked before condemning and removing the alternator.

These new pulleys allow the alternator to “free-wheel” or “overrun” when the belt suddenly slows down. This prevents the belt from slipping and reduces vibration. Best of all, the system needs less tension and you can even use a narrower belt. This can result in a 1.5% to 2% fuel economy improvement. However, these pulleys have a limited lifespan due to how they operate internally. 

OADs and OAPs behave the same, except the OAD will have a “spring feel” because of the internal spring. Testing can be performed on the vehicle with the belt attached.

Inspection Procedure

  1. Raise engine speed to 2,000-2,500 rpm in Park (auto trans) or Neutral (manual trans) and then shut off the engine. Listen for any noises from the OAD after the engine is shut off. A worn-out bearing will generate a “buzz” noise during this test. If the OAD is noisy during this test, replace it.
  2. Remove the cap, and with the proper tool inserted into the front of the OAP, rotate the alternator’s shaft in both directions. In the overrun direction, it should feel smooth and in the drive direction, it should have a spring feel.
  • If the pulley is locked up, replace it.
  • If the OAD has no spring feel in the drive direction, replace it.
  • If the OAD requires more than 9-13 in./lbs. (1-1.5 Nm) of torque to turn in the overrun direction, replace the OAD.
  • If the OAD is not smooth in the overrun direction, replace it.

Article courtesy Underhood Service.


Catalytic Converters: Efficiency Code Diagnostics

Understanding catalytic converter efficiency codes can be a long diagnostic road that can either lead to a happy customer or an expensive comeback. Chances are the original converter didn’t fail on its own, but conditions upstream hastened its demise. 

Almost every part on the engine determines how long the catalytic converter will last. It could be a faulty line of computer codes that pulses an injector too long or it could be a stuck piston ring allowing oil to be sucked into the combustion chamber. These little details can limit the life or efficiency rating of a catalytic converter. 

The Code

For a catalyst efficiency code to be set, a number of criteria must be met. The specific enabling criteria is different for almost every vehicle. For a code to be set, the oxygen or air/fuel sensor and the rear oxygen sensor must see a reduction in the efficiency of the converter. In other words, if the oxygen levels before and after the converter do not change, the converter is not working. 

But, this is not an automatic pass or fail. The oxygen sensors need to see this loss in efficiency over a number of drive cycle conditions. This is why it might take a few hours or a few days for the light to come back on after a code is erased. 

 On most vehicles, an efficiency code will not be set if an oxygen sensor heater code or any oxygen sensor-related code is set. Even if the converter is operating below 95% efficiency or the oxygen sensor is bad, the chances of the light coming right back on are slim. 

What is Efficiency?

The converter has an efficiency rating that is computed by the vehicle. This number rates the amount of reduction that is occurring in the converter and its ability to store oxygen. But, the efficiency of the converter is tied to the fuel trim of the engine. Most engines minutely alter the fuel trim to replenish the oxygen in the converter and to add fuel for reduction. This helps to keep the converter at the correct temperature for the most efficient operation.  

If an engine is running too rich, it cannot store oxygen. If it is running too lean, the reduction process might not occur due to an inability to heat up. If the engine is dealing with a leaking vacuum hose or a stuck injector, it can’t switch the fuel mixture properly to replenish oxygen and reduce harmful contaminates.

Converter efficiency can be checked with some scan tools along with the process of switching between rich and lean. Most converters start out at about 99% efficiency when new, and quickly taper off to about 95% efficiency after 4,000 miles or so of driving. As long as efficiency doesn’t drop off more than a few percentage points, the converter will do a good job of cleaning up the exhaust. But if efficiency drops much below 92%, it will usually turn on the MIL lamp.

Article courtesy Brake & Front End.


Nissan VQ35 Water Pump: Chain-Driven Replacement Procedure

At the top of the list of the engines with the most challenging water pumps to replace is the Nissan VQ-Series V6 engines. The water pump is turned by the timing chain and is nestled in the engine block. The VQ35-series of engines can be found in 2001-current Nissans and Infinitis. Book time on this job can range from 2-3 hours depending on the model and layout. There are no shortcuts. Advertisement

The first sign of water pump bearing failure will be a coolant leak coming from a hole in the block by the air conditioning bracket. This hole leads to the weep hole on the pump. The hole is between two seals that separate the oil on one side and the other side from the coolant. If the outer O-ring fails, it will leak coolant into the front cover area that is connected to the oil sump. This could mimic a head gasket leak.

When replacing the pump, pay close attention to the O-rings. These need to be lubricated with either oil or coolant. The rings need to be able to seal and move small amounts as the block heats and cools. Do not use silicone or other sealants – this can block the weep hole in the block.

Before starting the job, set the engine to top-dead-center. This can prevent the cams and engine from wanting to flop over when you release the slack on the chain. If you exceed 20º with the tensioner slacked, it could cause the chain to jump. 


1. Drain the coolant.

2. Remove the right engine cover.

3. Remove the coolant reservoir.

4. Remove any components or portions of the wiring harness that may block access.

5. On transverse-mounted engines, remove the tire and splash shield.

6. Remove the drive belts.

7. Remove the idler pulley, then the power steering and generator adjusting bars.

8. Support the engine and remove the front engine mount and bracket. 

9. Remove the water drain plug on the water pump side of the block.

10. Remove the chain tensioner cover and water pump cover.

11. Remove the chain tensioner assembly.

a. Pull the lever down and release the plunger stopper tab.

b. Insert a pin into the tensioner body hole to hold the lever and keep the stopper tab released (Figure 1).

c. Insert the plunger into the tensioner body by pressing the timing chain slack guide. 

d. Keep the slack guide pressed and hold the plunger in by pushing the stopper pin deeper through the lever and into the tensioner body hole.

e. Make a gap between the pump gear and timing chain by turning the crankshaft pulley approximately 20° counterclockwise (Figure 2).

12. Remove the chain tensioner. Be careful not to drop bolts inside the chain’s case (Figure 3).

13. Remove the three water pump bolts. Make a maximum gap between the water pump gear and timing chain by turning the crankshaft pulley counterclockwise until the timing chain loosens on the water pump sprocket.

14. Screw the bolts into the water pump’s upper and lower mounting bolt holes until they reach the timing chain case. Then, alternately tighten each bolt for a half turn and pull out the water pump. Pull straight out while preventing the vane from contacting the pump housing or chain.


1. Install new O-rings on the pump.

2. Apply engine oil and coolant to the O-rings as shown in Figure 4. Aftermarket pumps may have different colored O-rings.

3. Install the new water pump. Make sure the O-rings are in their grooves when installing the pump. Check that the timing chain and water pump sprocket are engaged. Insert the water pump by tightening the bolts alternately and evenly. Water pump bolts: 8.5-10.7 Nm (75-95 in.-lbs.)

4. Remove dust and foreign material entirely from the backside of chain tensioner and the installation area.

5. Turn the crankshaft pulley approximately 20° counterclockwise so that the timing chain on the timing chain tensioner side is loose.

6. Install the timing chain tensioner. Timing chain tensioner bolts: 7.0-9.3 Nm (62-82 in.-lbs.)

7. Remove the stopper pin.

8. Install the chain tensioner and water pump cover. Remove the old sealant and apply new. 

9. Refill the engine with coolant.

10. Start the engine. You may hear the timing chain rattle at first. Rev the engine to 3,000 rpm to purge the air from the chain tensioner. 

Article courtesy ImportCar.

Automotive Video

VIDEO: Inspection Before Disassembly

One of the most forgotten steps before replacing a head gasket is to inspect the entire engine before removing the head and intake manifold. Andrew Markel covers what to look for under the hood, under the car and in the ECM. Sponsored by MAHLE.

Video courtesy ImportCar.


Diagnosing Volkswagen Idle Quality Problems

Idle quality is challenging to diagnose because it is a vague description at best on most Volkswagens. The textbook definition is an engine speed lower or higher than the specification in the service manual. For drivers, idle “quality” is more difficult to define.

Idle quality could be classified as vibration. However, vibrations can be caused by multiple components, including broken engine mounts. Running conditions that cause misfires can also cause “rough running” or a vibration felt by the driver. Capturing a driver’s complaint and replicating it is critical. Knowing when the idle quality issue occurs is just as crucial of how it feels.

How is idle speed controlled?

Volkswagen fuel injected engines can regulate the idle speed two ways. Some engines have an idle air control or idle stabilization valve. These valves are bypasses around the throttle plate. The flow is controlled by an electric motor. Most late-model Volkswagen throttle by wire systems might not have an idle control system. The angle of the throttle plate is used to control idle speeds. The amount of air allowed to pass for the idling of the engine is typically displayed as a data PID that can be a percentage or angle on a scan tool.

Changing the amount of air means changing the amount of fuel. To create the optimal idle mixture, the engine control module will adjust the open time of the injectors. If the mixture is too rich or too lean, the resulting misfire will create a rough idle.

How is idle speed setting determined?

Idle is not just a number that the engine control module tries to match. The goal of the ECU is to keep the idle speed consistent under changing engine loads from the A/C compressor, alternator and other components. These loads are predictable and anticipated. When an A/C compressor is given the command to engage, the ECM will increase airflow and fuel to the engine. This is usually undetectable by the driver. There are expected loads, and unexpected loads or changes inside the engine that change the idle.

The ECM knows how much suction should be produced by the throttle position data for the engine speed. The amount of air sucked in can change if the pump is not operating correctly. Changes to camshaft timing, restriction in the exhaust or burnt intake valves can change the amount of air required to keep the engine idling smoothly.

The air is measured by a manifold air pressure (MAP)or mass airflow sensor (MAS). A MAP measures negative pressure. A MAS measures the amount of air flowing through intake before the throttle plate. Some engines have both a MAP and MAS.

Some of the greatest idle quality killers are leaks in the intake manifold. To a MAS sensor, the air coming through is unmetered, and the ECU thinks the engine is running too lean so it adds fuel. To a MAP sensor, the leak is seen as a signal the engine is using less air so it takes away fuel. These strategies can result in a change in the quality of the idle. A MAS-only system may have a high idle. A MAP system might stumble and run rough. Modern systems are better at controlling the idle and compensating for the problem, so it will not leave the driver stranded. But, it will still run rough and it will turn on the check engine light.  


Between combustion events, every engine slows down just a tiny amount. If a cylinder is not firing, it slows down even more but still has to speed up when the next cylinder is fired. This makes for a very poor idle. The cylinder can often be isolated using misfire codes or using the misfire counters. 

Courtesy of Brake & Front End.


Fuel Filters And Frequency Cycles

On most import vehicles, the three components with the highest manufacturing tolerances are ABS brake modulators, direct injection high-pressure fuel pumps and fuel injectors. All of these components are at the mercy of the fluids that circulate inside their respective systems. While the brake system is closed, a fuel system will pump thousands of gallons of gasoline in the first 100,000 miles.

Filtering out dirt and debris from the gasoline is essential to both the life of the fuel system and engine. Even a small speck of dirt, the size of the width of a human hair, can impair the spray pattern of a fuel injector or damage the surfaces inside a fuel pump. Fuel filters and screens inside injectors and pumps prevent damage from occurring.  

You may have noticed that some late-model Asian and European imports now lack a fuel filter between the pump and fuel rail. In theory, many imports should not need an inline fuel filter because of internal and external factors. 

One of the internal factors is plastic fuel tanks. By not having metal fuel tanks, corrosion inside the tank is eliminated. But it does not mean tanks are impervious to debris entering the tank from the filler neck. The other internal factor is that manufacturers are doing more filtration before the fuel enters the pump. Externally, underground fuel tanks have been improved to prevent internal corrosion and leaks. In the late 1980s, the EPA started to mandate better tanks to prevent ground water contamination. Also, modern gas pumps filter the fuel before pumping it into the tank. 

The new filtration strategy is to trap contaminates before the fuel pump pressurizes the fuel. Older socks or strainers were designed to catch contaminates between 50-100 microns in diameter. Forty microns is equivilant to the size of a human hair. Newer pre-pump strainers or socks can now capture smaller debris and more of it.

If a vehicle has a fuel filter, replace the filter after the pump has been replaced. It sounds simple, but this is often forgotten. The old filter can restrict flow and make the new pump work harder. Restrictions caused by a clogged filter makes for a hotter running pump because most modern systems use a pulse-width modulated voltage to the pump. If the engine management system is not seeing enough fuel pressure at the rail or the fuel trim is too lean, the computer will increase the frequency and duty cycle to the pump to increase fuel pressure. 

Courtesy of Brake & Front End.