In 2003, increased emission standards forced Ford to stop offering the 7.3L Powerstroke in MY Ford trucks. Instead, the company turned to the up and coming 6.0L Power Stroke. Little was known just how big of a disaster this would be for Ford’s reputation.

While the 6.0L was only offered for a period of four years in the Super Duty truck, many problems arose from the new Hydraulically acutated, Electrically controlled Unit Injector (HEUI) engine design that would cripple the dependability of the Ford diesel pickup. Even though the 6.0L was cutting edge technology producing more power in a smaller package, the engine was plagued with various hiccups that destroyed its reputation and still carries this reputation with it today. For the 2008 MY Ford Super Duty pickup, a new engine, the 6.4L Powerstroke would emerge. But, how much is really known about the engine? The 6.4L engine was very short lived and only offered until 2010.

Before going any further, there is something that you have to realize. Manufacturers of on-road diesel engines were grasping for straws. Clean air standards for diesel engines have become tougher to meet. The biggest factor for Clean Air of a diesel engine is to lower NOx gas and particulate matter from the exhaust system. The 6.0L was designed to lower NOx emissions by incorporating an EGR (Exhaust Gas Recirculation) system. The engine was smaller in

displacement, with four valves per cylinder, direct injection and variable geometric turbocharger. NOx gas emissions could be drastically reduced by reintroducing exhaust gas back into the engine to be re-burned. The only problem is that exhaust gas displaces the oxygen causing a cooler burn, which may lower NOx but in turn cause soot. So, the 6.0L engine became a problem because it would not meet particulate matter standards that would go into effect for 2008. The 6.4L would take its place with a little more displacement, four valves per cylinder, sequential turbo system, high-pressure common rail fuel injection, EGR and DPF.

When you open the hood of a 2008 Ford truck, you realize that the 6.4L was a big change. You may not even recognize any parts of the engine that you are commonly familiar with other than maybe the turbo or the air filter. The 6.4L was definitely unique, but just how different was it from the 6.0L? The short block of the 6.4L engine is basically the same as the 6.0L. The bore was increased from 3.74” to 3.87” with the stroke remaining the same at 4.134” The piston design was very similar, but compression ratio was lowered to 17.5:1 instead of 18.0:1. Firing order remained the same being 1,2,7,3,4,5,6,8. The passenger side is the odd numbered cylinders 1,3,5,7 and the driver’s side cylinders are even numbered 2,4,6,8.

The other components of the engine are where the major changes take place. The cylinder heads are still designed with four valves per cylinder, but the 6.4L is not a HEUI design, it is a high-pressure Common-Rail.

High-Pressure Common-Rail consists of a network of precision components that enable fuel to be injected under extreme pressure, which ranges from 5,000 psi to 30,000 psi. The high-pressure fuel pump is driven by the rear gear train and mounted in the same place as the HPOP in the 6.0L. The high-pressure fuel pump consists of a VCV (Volume Control Valve), which controls the volume of fuel entering the pump and a PCV (Pressure Control Valve), which controls pressure the pump produces. As fuel enters the pump, it is then

pressurized and sent to the fuel rails attached to the cylinder heads located underneath the valve covers. The 6.4L has a Piezo Electric injector mounted in the center of the valves directed in the middle of the combustion chamber just like the 6.0L. A high-pressure line connects the high-pressure fuel rail to the injector. The injector is held in place with a hold down clamp and is sealed with an O-ring. The piezo electric injectors are extremely precise with the ability to actuate five times per combustion event.

The path of fuel flow is also unique compared to the 6.0L. The fuel pump on the driver’s side frame rail takes fuel out of the tank and pressurizes it to the secondary filter housing located on top of the engine much like the 6.0L. From the secondary filter housing, fuel is then sent to the high-pressure fuel pump. Returning fuel from the high-pressure pump joins fuel returning from the injectors from lines in the front of the cylinder heads. The returning fuel goes through a secondary cooling system, which is located on top of the turbo at the firewall of the driver’s side. This is done because high fuel pressures increase the temperature of diesel fuel.

Hot fuel will lose its lubricity and lock up the high-pressure pump. The secondary cooling system consists a fuel cooler that is circulated with engine coolant, a coolant bottle and a circulation pump, which is mounted behind the fuel radiator, which is mounted on the driver’s side of the charge air cooler. When fuel temperature reaches 77 degrees F, the coolant pump turns on. When fuel temperature reaches 68 degrees F, the pump turns off. If fuel temperature reaches 151 degrees F, the engine fan comes on, and if the fuel temperature reaches 194 degrees F, the engine loses power and the check engine light

comes on and doesn’t go off.

Fuel also has to be super clean for the common-rail system. The primary fuel filter is rated at 10 micron and the secondary fuel filter is rated at 4 micron. Any contaminants larger than 4 micron can score the components in the fuel system.

Another interesting change was the function of the turbocharger. The 6.4L was often referred to as twin turbo, but the proper name would be a sequential turbo system. The object of the sequential turbo system is to take a small turbo and feed a larger turbo. Some may refer to this system as “compounding.” When you feed a larger turbo with a smaller one, you are trying to produce optimum boost with little or no turbo lag. The smaller turbo is considered low pressure and the bigger turbo high pressure. The high-pressure turbo contains vanes much like the turbo from the 6.0L. As the vanes open and close, they control the effective size of the housing. The vanes are controlled by an actuator linked to a pivot arm, which is connected to an unison ring that moves the vanes. The actuator is controlled by the PCM, which is cooled by the coolant system to protect the electronics.

Here is a brief summary of how the turbocharging system works:

• Air enters the low-pressure turbo from the air filter

• The low-pressure turbo compresses the air and sends it through an extension tube where it enters the high-pressure turbo

• The high-pressure turbo further compresses the air and sends it to the CAC (Charge Air Cooler) before

entering the intake manifold

During operation at low engine speed, there is little energy available from the exhaust to generate boost. In order to utilize the small amount of exhaust energy, the turbo actuator will be commanded to close the vanes of the high-pressure turbo. This causes a pressure increase in the exhaust housing of the turbo which will increase the turbine wheel speed causing the high pressure turbo to act like a small one and provide boost. At medium engine speed, the actuator will be commanded to partially open the vanes. This will provide the correct amount of boost for proper engine operation and EGR function. During high engine speed, the actuator will be commanded to open the vanes completely and the turbo will act as a big turbo with minimum restriction while providing maximum boost.

The exhaust system routing also influences turbo operation and proper emission function.  As exhaust exits the cylinders, it travels into the exhaust manifolds and then into the exhaust “up” pipes. The “up” pipes feed exhaust into the high-pressure turbine housing and then into the low-pressure turbine housing where it exits into the “downpipe,” which carries the exhaust to the exhaust system.

On the passenger side “up” pipe, there is a branch that carries exhaust through an EDOC (EGR Diesel Oxidation Catalyst) and then to the horizontal EGR cooler. The purpose of the EDOC is to crack hydrocarbons of the exhaust gas before entering the EGR coolers. Exhaust gas then flows out of the horizontal cooler and enters the EGR vertical cooler.

As exhaust gas exits the vertical cooler, it is stopped by the EGR valve where it will enter the engine when the PCM commands the EGR valve to open. The purpose of the EGR function is to lower NOx emissions of the exhaust gas by letting the engine re-burn the exhaust gas. The purpose of the two EGR coolers is to lower temperature of the exhaust gas before it enters the intake manifold. Both of the coolers along with the EGR valve is cooled by coolant from the cooling system. Under load, exhaust gas temperatures can be extremely hot and the coolers can remove up to 850 degrees F of temperature before reaching the intake.

When the exhaust gas exits the low-pressure turbo into the downpipe, it passes into the DOC (Diesel Oxidation Catalyst). The purpose of the DOC is to remove hydrocarbons but also ramp up temperature to burn off soot in the DPR (Diesel Particulate Filter). The DPF filters particulates from the exhaust gas known as soot. Soot builds up over time and must be burned and turned into gas. This process is known as regeneration.

There are two types of regeneration: passive and active. Passive regeneration happens at normal driving when the exhaust temperature is hot enough for the DOC to burn off the soot build up in the DPF. Active regeneration

occurs when the DPF becomes restricted and the exhaust temperature is not hot enough such as short distance trips or long idle time. During active regeneration, a change is heard in the exhaust system and the engine idle ramps up. The injectors are commanded to inject fuel into the engine on the exhaust stroke, which will put raw fuel into the DOC. This causes the DOC temperature to increase, which will burn off soot trapped in the DPF.

One thing to note here is that the exhaust tips at the passenger side rear wheel have windows notched in them. These windows are known as “tip diffusers,” which are used to draw in cool air to help cool the exhaust gas exiting the tips. Temperatures at the tip can become very high, so this helps cool the exiting gas. It is not recommended to change or modify these tips and keep them clear of debris.

The 6.4L was a juiced up 6.0L and Ford had tried to address a lot of the failures of the 6.0 liter in this engine. The 6.4 had a totally reconstructed EGR cooler system, bigger head bolts, different turbo configuration, different fuel system, bigger flexplate, and cooling system. These were all in response to the fact that the 6.0L had too small of head bolts, a turbo that would stick and had to be removed and cleaned, an EGR cooler that would failand injectors that would stick due to the HEUI design.

When it really comes down to it, the only thing the 6.4L has in common with the 6.0L are a few components

of the short block. It was best described as a 6.0L on steroids.

Very special thanks to Brent Burich and all the technical experts at Blue Diamond for invaluable assistance with this project.