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The 6.4L Powerstroke                   http://firstcoastdieselperformance.com/

by Rob Gaskell, Jr. and Rob Gaskell, Sr.                                       Special thank's to Adam Brannan at First Coast Diesel Performance for contributing to this article.

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The 6.4L Powerstroke was released in model year 2008 as a replacement for Ford's 6.0L Powerstroke, and uses a Common-Rail Diesel injection system which is new to the Powerstroke namesake, in conjunction with other new and familiar engine and emissions controls. The 6.4L was a response to several reliability issues which the 6.0L PSD had, as well as new, more strict emissions standards for light duty diesel trucks in North America. Just as with the release of the 6.0L, Ford also made sure to derive more power than ever before out of the engine brand which gets its name from the power stroke of an internal combustion engine, an important concern with competitors continuing to upgrade the horsepower in their existing engine platforms.

Despite the efforts of Ford and International/Navistar, the 6.4 Liter (Litre) has shown some reliability issues, many of which are similar to the issues seen in the 6.0L, though some are unique. These issues can actually be more costly to repair than those on the 6.0L, leading many owners to consider replacing their 6.4 L powered Super Duty trucks with a different make. This is generally not the most economic option, since the original purchase price of these trucks is very high, and has depreciated significantly due to the reliability concerns surrounding the engine. By proactively upgrading, performing maintenance beyond manufacturer specifications and responding quickly to trouble symptoms, the 6.4L Powerstroke can be made very reliable at a cost which is more economical than taking a loss on the truck and gaining a new truck payment.

With all the problems with the previous 6.0l right out of the gate, we had hoped to see significant gains in reliability with the introduction of the 6.4l. for the most part this has been the case however there have been some issues which have lead to catastrophic engine failure. many of these failures can be attributed to improper or lack of maintainance. there are also many cases where components have failed and lead to engine failure as well. the best way to avoid this scenario is to follow Fords service recommendations to the letter and keep records if serviced by you or a facility other than the Ford dealer. this will aid in attaining warranty should an issue arise.

The Operation

The 6.4L Powerstroke differs greatly from previous Powerstroke engines, particularly in its use of a Siemens-designed Common-Rail Diesel fuel injection system. The 6.4L does use many other systems which are similar to the 6.0L Powerstroke, such as an Exhaust Gas Recirculation (EGR) system, as well as a Variable Geometry Turbocharger (VGT). This section provides a brief overview on the operation of the 6.4L and its sub-systems. For problems associated with these and other systems, as well as solutions to these problems, read the Issues and Answers sections below.

Fuel System Operation

The 6.4L Common-Rail Diesel fuel system uses 3 main components, including a fuel lift pump, a high-pressure fuel pump, and 8 electronic fuel injectors. For more on Common-Rail Diesel systems, see our Common-Rail Diesel Systems article. This platform had a number of first's in the light heavy duty tuck market, most notably a two point high pressure control system.this system allows for much faster response to changing needs and driver input

The fuel lift pump is mounted to the frame under the left-hand side of the cab. This pump delivers low-pressure fuel to the high-pressure fuel pump, through two fuel filters.

The high-pressure fuel pump, or fuel injection pump, pressurizes fuel and and delivers it to a pair of fuel rails, mounted under the valve covers. The fuel rail pressure (FRP) is controlled by a pair of valves located on the inlet and outlet of the fuel injection pump. These valves control the amount of fuel which is allowed to enter the fuel injection pump, as well as the amount of fuel which is delivered to the fuel rails on the outlet side of the fuel injection pump. Excess fuel from the fuel injection pump is delivered to a fuel cooler before it is returned to the fuel tank.

The fuel injectors on the 6.4L receive a constant supply of high-pressure fuel which is stored in the fuel rails. The fuel injectors are opened and closed eletronically, with the amount of fuel delivered to the combustion chamber being controlled by a combination of fuel rail pressure and fuel injector pulse-width, which describes the amount of time the fuel injectors are open.

Variable Geometry Turbo Operation

The 6.4L uses two turbochargers, one of which is a variable geometry turbocharger. The VGT uses an electronically controlled actuator, thereby controlling turbocharger speed as well as exhaust backpressure and intake manifold boost pressure. The VGT is also used in conjunction with the EGR valve to control EGR system operation. The system also incorporates a throttle plate the aid in EGR Flow.

Exhaust Gas Recirculation System Operation

The EGR system on the 6.4L uses 4 main components, including an EGR valve, a pair of EGR coolers, a throttle plate as well as the VGT. The EGR system is designed to lower combustion temperatures, thereby reducing the production of oxides of nitrogen, which contribute to smog and acid rain. For more on this, read our Exhaust Emissions article.

The EGR valve controls the flow of exhaust gases into the intake manifold. These exhaust gases must flow through the EGR coolers, which are coolant-to-exhaust coolers that are designed to lower the temperature of the exhaust gases, thereby increasing the EGR system's ability to lower combustion temperatures. The VGT enables the flow of these exhaust gases by increasing exhaust backpressure, which must be higher than intake manifold boost pressure in order for exhaust gases to flow into the intake. EGR flow is then operated by a combination of VGT exhaust and boost pressure control, Throttle plate position as well as EGR valve position.

Engine Oil Cooler Operation

The 6.4L uses a coolant-to-oil engine oil cooler, which is mounted at the front of the engine valley below the oil filter housing. Small passages inside the heat exchanger portion of the engine oil cooler flow coolant and engine oil, allowing heat from the engine oil to be transferred into the coolant. Coolant then exits the engine oil cooler, and enters the EGR cooler. Proper cooling of the engine oil on the 6.4L is critical, since this oil is used to cool internal engine components which engine coolant cannot reach. For more on engine oil cooler operation, see the Issues and Answers sections below.

The Issues

Cooling System Issues

There were radiator failures on some of the early build trucks.the root cause of these failures was later determined to be hyper- extention of the by-pass thermostat. this would cause the primary thermostat to oscillate leading to thermal spikes within the cooling system and stress on the radiator. any of the F 250-F 550 with the 6.4l Diesel, 2008-2010 may experience radiator failure.  the addition of a veturi tee, replacement of thermostat's and radiator on early build trucks (on or before 9/14/09) was done. Cause for radiator failure's in later build trucks have usually been related to coolant leaks in other parts of the cooling system. low coolant levels cause temerature spikes which can stress the radiator.The EGR valve itself is water cooled and we have seen a few of them develope cracks. there are also hose connections around the engine that can develope leaks.. Oil cooler failures are not nearly as common as they were on the 6.0l but we have seen several rupture type failures, though at this point plugging of the coolant passages has not been much of an issue.  A rupture in the oil cooler heat exchanger will allow engine oil into the cooling system and if left unchecked will destroy all the rubber hoses in the system. If the condition is caught early enough, there are a few methods for cleaning the system that work very well. It is important that the cleaning be done properly to ensure all motor oil has been removed from the cooling system to prevent hose degradation and and eventual failure. Bulletproof Diesel does make an upgraded oil cooler for this application which is a liquid cooled, externally mounted unit, but at this point I see no real value in this upgrade. this may change as these trucks age and as emerging issues present themselves.

Maintaining coolant at proper intervals is very important on the 6.0l and 6.4l. Nitrate levels should be checked on a regular basis. I recommend a complete flush of the cooling system and replacement of the silicate based coolant on the 6.4l with one of the high quality extended life coolant's. silicate based coolant will degrade and drop silicates which can ultimately wind up in the oil heat exchanger, restricting flow or wind up as sediment in the heater core, etc. I've yet to see the recommended coolant go the distance, 5 years, 100,000 miles. We have seen cavitation behind the water pump on both the 6.0l and 6.4l , It's not a common issue and only seems to be on engines with 100,000 miles plus and with obvious coolant neglect. the importance of a properly maintained cooling system cannot be over stressed.

EGR Cooler Issues

The 6.4L Powerstroke has two EGR coolers, the lower of which is mounted to the left side exhaust manifold, failure of which can lead to coolant loss, overheating, and other serious engine damage. Common symptoms include steam from the exhaust while driving, as well as coolant loss with no evidence of external leakage. The EGR cooler uses engine coolant to cool exhaust gases which are reintroduced into the engine's intake to cool combustion temperatures and reduce nitrous oxide emissions.

This lower EGR cooler commonly fails due to overheating and boiling of the coolant inside it, rupturing it and causing coolant to leak into the exhaust manifold. Because the cooler is mounted relatively low on the engine, a significant amount of coolant may leak out of the cooler, causing large amounts of steam to exit the exhaust system, and potential engine overheating due to low coolant levels. Thes symptoms can also be a sign of blown head gaskets, and this condition should always be tested for, even if the EGR coolers are known to be leaking. If the cooler leaks while the engine is not running, this coolant can enter engine cylinders through open exhaust valves. Attempting to start the engine after coolant has entered a cylinder can lead to hydrolocking, where the incompressible coolant in the cylinder stops the engine from turning. The affected cylinder's connecting rod may bend as a result, requiring significant internal engine repairs or engine replacement to correct.

Turbocharger Issues

The 6.4L uses two turbochargers, the smaller of which is a Variable Geometry Turbo. This VGT has not had nearly the sticking issues that the 6.0l turbo has suffered. most of the turbo issues can be attributed  failed VGT actuators, temperature related failures of seals, bearing and turbine wheel.many of these failures can be directly attributed to DPF regeneration and elevated exhaust system temperatures.

Head Gasket Issues

Head gasket failure, also known as "blown head gaskets," on the 6.4L Powerstroke is relatively rare on the 6.4L when compared to the 6.0L, but can potentially result from similar circumstances as 6.0L head gasket failures. Any engine overheating or localized overheating as described above are most likely to lead to head gasket failure, particularly when left unnoticed or left unrepaired for longer periods of time. It is essential that machining of the cylinder head surfaces is performed when replacing head gaskets, despite Ford's stance that the heads cannot be machined. While we here at Fleet Service Northwest, Inc. have only seen two cases of head gasket failure, it should be noted that the severity of this issue on the 6.0L was not fully realized until 2 or 3 years ago, when the oldest of these engines was 5 or more years old. As 6.4Liter Powerstrokes see higher mileage and longer service lives over the next few years, we may see more instances of these failures. On the other hand, the larger head bolts which the 6.4L uses may prevent this problem from becoming widespread.

Other major fuel injector failure issues include leakage of excess fuel into the combustion chamber while the engine is running or stopped, which can also lead to severe engine damage. Hard starts, rough engine idle and misfires are symptoms the driver is likely to note due to leaking fuel injectors. The best way to prevent fuel injector problems is to replace fuel filters frequently, using only Motorcraft fuel filters, and avoid using low-quality fuels such as off-road diesels or questionably-sourced biodiesels, as fuel acts as a lubricant for the many precision components found in a common-rail fuel injector.

Excess fuel entering a cylinder from a leaking injector while the engine is running can cause that cylinder to overheat, leading to catastrophic failure of the piston or engine seizure. Excess fuel entering the cylinder while the engine is not running can cause hydrolocking and may bend connecting rods, similarly to EGR cooler leakage described above. It is important to note that major engine damage has resulted frequently on the 6.4L due to leaking injectors without any indicator lights such as the check engine light ever illuminating. This makes it essential that the driver proactively address rough idle, hard starting, and other engine performance issues early before they cause major damage. This includes stopping the vehicle and having it towed to a qualified repair facility if there is a serious misfire or other engine performance issue, as a tow bill is far less expensive than engine replacement.

Similar to fuel injector failure, the fuel injection pump is also prone to failure due to fuel quality and fuel filter concerns. The pumps may seize, causing the engine to stop suddenly, particularly at high operating temperatures, and may actually restart when the engine cools off. It is essential that this problem be diagnosed immediately, as attempting to run the engine after the fuel injection pump has seized is likely to result in immediate, catastrophic failure of the pump, which can cause damage to other fuel system and engine components.

Additionally, the fuel lines which feed the injectors from the high pressure fuel rail are prone to leak into the engine crankcase, which can dilute the engine oil and lead to major engine damage. The easiest way to detect this is by checking engine oil regularly, as overfull engine oil is a likely sign of this problem. The fuel lines are mounted under the valve covers, and as a result fuel will leak into the engine crankcase causing oil delution and can lead to major engine damage, without visible fuel leakage to the outside of the engine.

 There have been significant improvements to the operating system of the 6.4l Powerstroke Diesel to date. These changes have greatly improved the reliability of this platform. One of the  best ways you can ensure reliability on any 6.4l, regardless of whether its stock, or not is to follow the manufacturers recommended service schedule. many of the catostrophic failures can be attributed to improper or lack of maintenance. 

DPF Delete/Tuning

There are aftermarket DPF delete kits which are available, these require software which turns off DPF regeneration, some even have the option to disable EGR function. the descision to delete and install these  products is not one that should be made lighty. there are warranty considerations and it is a violation of EPA  emissions tampering laws to disable these systems. if you live in a state or area which does not have I/M inspections, it will probably never be an issue. There is also software available which improves economy and performance while keeping the emissions system intact and fully functional for those who might be looking for improvements but live in an area which requires emissions testing.

The general consensus among 6.4l diesel truck enthusiat's/owners,company's who build software and delete kits and supporting data all show deleting these systems has proven to significantly improve economy, performance and reliability. Keep in kind you will most likely be denied any powertrain warranty coverage on the 6.4l diesel if you've run an aftermarket tuning device, intake system or emissions system delete. there are some dealers who will push claims through with these modifications but it has become very difficult do to the cost of warranty repairs and abuse, so this should be considered before you choose to modify your truck. If you are running a stock truck it is very important you have the latest software updates( flash). even if your truck is no longer under warranty it is well worth the cost to keep the powertrain control system up to date and will enhance the performance and durability of this platform.Ford has done an outstanding job of supporting the 6.0l and the 6.4l with software upgrades.

EGR Cooler Answers

The EGR Cooler is a  significant source of Powerstroke trouble which Bulletproof Diesel has addressed for both the 6.0L and 6.4L engines. The Bulletproof EGR coolers for both engines feature lifetime warranties, and have already proven to be a great way to permanently solve an otherwise recurring problem with these engines. The Bulletproof coolers accomplish this through much more robust construction than the stock coolers, and by holding a higher volume of coolant, reducing the likelyhood of coolant boiling within the cooler. This is done without taking up additional space within the engine compartment, as the Bulletproof EGR coolers are actually made by replacing the internal components in a stock cooler.

Bulletproof Diesel products are available for installation or purchase from Fleet Service Northwest, Inc.

Check out our Ford Diesel Store for details.

Turbocharger Answers

While options for upgrading the turbochargers on the 6.4L are extremely limited and unlikely to provide any significant reliability improvements, there are preventive steps that can be taken to reduce the recurrence of turbocharger problems. First, running good quality Ultra-Low Sulfur Diesel, maintaining clean fuel filters, and avoiding fuel system contamination can reduce the production of carbon, lessening the slow buildup of cabon inside the VGT. Addressing misfires, smoke, and low power conditions as quickly as possible can also help prevent rapid buildup of carbon, along with potentially avoiding other serious engine damage that can result from these conditions. For more on this, see the Fuel Injection System section below. Use of performance programmers and tuners should also be done with care, and exhaust gas temperature, or "pyro" monitors should be installed and observed by the driver under hard acceleration, when towing, or when pulling hills when using increased-horsepower settings.

Head Gasket Answers

While the 6.4L Powerstroke appears to be significantly less prone to head gasket failures over the 6.0L, cooling system problems as well as high-performance tunes can increase the likelihood of this problem. Fleet Service Northwest recommends installation of ARP head studs any time cylinder heads are removed from the 6.4L. ARP head studs have proven themselves to be the solution to head gasket failure on the 6.0L over the last several years, and are often installed proactively on that engine.

Fuel Injection System Answers

The many problems that both affect and are caused by the fuel system on the 6.4L Powerstroke are of great concern to all 6.4L Powerstroke owners, and are largely preventable through extra preventive care that goes beyond manufacturer-recommended maintenance. As stated above, fuel injection system components are lubricated by fuel, and are sensitive to fuel shortages and fuel quality issues. Using Motorcraft fuel filters and replacing them frequently is a good way to lessen the risk of fuel system damage. Motorcraft fuel filters for both the 6.0L and 6.4L have patented features that are not available even on high-quality aftermarket filters, and as a result, filter water better than most aftermarket filters. It should be noted that Ford recommends draining of the HFCM module should be done every 30 days. while in use. they did not make this task very convenient on the F Series, However it should be done. If you experience a major fuel system failure on the 6.4l , there is a very high probability you will be paying for this repair yourself. this is why it is important for you to follow the recommended fuel system service intervals.

Fuel quality and refueling practices are of equal importance, since contaminants in fuel both cause direct damage and will cause fuel filters to clog more quickly. Fuel shortages due to clogged filters cause high-pressure fuel components to run without lubrication. For this reason, it is essential that only Ultra-Low Sulfur Diesel is run in 6.4L Powerstroke engines, and that fuel filler caps be kept clean and in good condition. Many biodiesels, along with Low-Sulfur Diesel (as opposed to Ultra-Low-Sulfur Diesel), may contain particles which can not only accelerate filter clogging, but can also cause faster wear of precision fuel injection components as some particles will always manage to get past the filter. Fuel supplied by some mobile refueling services can also be problematic if their tanks are not properly maintained and fuel is not properly filtered as it is dispensed. Similarly, refueling in the field from fuel cans should be done with care and as infrequently as possible, since contaminants can easily enter the fuel can or the vehicle's fuel filler neck, particularly at dusty or dirty jobsites. Sealing surfaces of fuel filler caps should also be checked periodically for wear, since dust and debris can enter the fuel filler via a worn fuel filler cap seal.

Checking engine oil on a regular basis and servicing the engine with Motorcraft's Super Duty Diesel Engine Oil is a great way to protect the engine from wear and damage, including damage due to leaking fuel system components. If engine oil is overfull, or appears thin, this may be a sign of fuel system leakage into the crankcase, among other problems that could lead to major engine damage. Catching these problems as early as possible will prevent damage and extend the life of your 6.4L Powerstroke.