The Power Stroke Blues: 6.4L Edition

When the 6.4L Power Stroke was introduced in 2007 (for ’08 model year Ford Super Duty’s), it had a lot to live up to. After a five-year production run of the 6.0L Power Stroke brought failure after failure to light, the Ford faithful — who were ready to usher in a new, hopefully more reliable power plant — leapt at the chance to get their hands on them. While the 6.4L V8’s compound turbocharger arrangement, common-rail injection system and 350hp and 650 lb-ft looked good on paper (and 550 to 600 horsepower eventually being achieved with just a programmer), the honeymoon was short-lived.

Failed emissions control components, fuel system contaminants and corrosion, leaking radiators and hoses, cracked turbo up-pipes and severe oil dilution all plague the 6.4L Power Stroke — and the problems only get worse with age. In most cases, the engine itself suffers some type of catastrophic failure between 150,000 to 200,000 miles. And because the repair costs on a 6.4L are so high (often double what they would be on a 6.0L Power Stroke), many owners simply walk away from the truck.

Read on for a closer look at the 6.4L’s most notorious failure points and what you should be on the lookout for if you own one or plan to buy one.

Pop a Top (Again)

It’s important to know that the ’08-’10 Super Duty’s were designed to have the cabs pulled to perform most major engine repairs. And while we agree with Ford that pulling the cab allows a technician more working space and enough room to perform virtually any engine-related repair more efficiently, it does add four to eight hours worth of labor to the job (depending on the shop you use).

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Sure, any of the following problems can be tackled with the cab still attached to the frame, but most techs opt to do the work cab-off.

Diesel Particulate Filter (DPF)

We would be remiss if we didn’t start off by saying the emissions control devices cause most of the 6.4L’s reliability and performance related problems. At the heart of several major failure points rests the exhaust after treatment system, specifically the diesel particulate filter (DPF). Designed to collect soot from the engine’s exhaust, the DPF requires what is called a regeneration mode to take place in order to turn the collected soot into a fine ash — otherwise the DPF would fill up, rapidly.

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During the regeneration process (also known as regen or exhaust filter cleaning), fuel is used to effectively turn a portion of the after treatment system into an incinerator to burn off the accumulated particulates in the DPF. To make this possible, fuel is injected on the engine’s exhaust stroke (i.e. diesel is allowed to exit through the exhaust valves, route through the manifolds, turbochargers, and ultimately the exhaust system). When this happens, the engine sees elevated exhaust gas temperature, higher idle rpm, a reduction in power, lower fuel economy and in some cases, smoke out the tailpipe.

Inevitable Failure

As with any exhaust after treatment system behind a modern diesel engine, eventually the DPF will plug solid and need to be replaced. Unfortunately, failure is inevitable with this component.

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(Photo: Ford Motor Company)

Once plugged, the DPF will force the truck to remain in perpetual regen mode. This means the engine constantly sees 1,200 to 1,400-degree exhaust gas temperatures and extreme back pressure, which overtime takes its toll on everything from the engine oil to the turbochargers.

2 EGR Coolers = 2 Failure Points

Even though the 6.4L makes use of two EGR coolers (as opposed to one, highly-prone-to-failure unit found on the 6.0L), they still plug up and/or crack.

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It’s most common for the horizontally mounted EGR cooler (shown on the bottom) to fail due to it being the first unit exposed to incoming exhaust gases. The horizontal EGR cooler is located above the driver side exhaust manifold.

Water + Metal = Rust

While the use of piezoelectric fuel injectors used in the 6.4L can pull off five precise injection events per combustion cycle, their tight tolerances mean they don’t take kindly to contaminants.

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A neglected or clogged drain in the water separator (along the driver side frame rail) will eventually allow water to pass through and enter the fuel system. While there, it reacts with the metal components of the injection system and forms rust, which can take out the injection pump, injectors or (in some extreme cases) the entire engine.

High-Dollar Fuel Injection System

The primary reason for the 6.4L’s immense repair costs spawns from the high price tag of its parts. Take the engine’s high-pressure fuel pump (i.e. injection pump), the K16 built by Siemens, for instance. The cost of a reputable, remanufactured replacement pump is between $1,600 to $1,700.

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By comparison, the Bosch CP3 high-pressure fuel pump used on the ’01-’10 6.6L Duramax and ’03-‘present 5.9L and 6.7L Cummins would only run you $525 to $750 in remanufactured form.

The $6,000 Fix

Unfortunately, the K16 doesn’t have nearly the reputation for durability that the Bosch CP3 does, and the 6.4L’s turbochargers have to be pulled in order to access it. Most failures stem from a lack of low-pressure fuel supply via a failing lift pump or a stuck pressure control valve (PCV) or volume control valve (VCV). And since the PCV and VCV aren’t considered “serviceable,” all-out pump replacement is often the only solution.

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A K16 pump that is in its death throes will typically produce a P0088 diagnostic trouble code. Like the injectors, the K16 does not tolerate contaminants well, and plenty of pump failures have been traced back to rust being present in the low-pressure fuel system (what feeds the K16). When this pump comes apart it sends shrapnel through the injectors, effectively taking them out at the same time. The parts and labor for a new high-pressure fuel system (along with a complete flush of the fuel tank) will run you $6,000 or more.

The Labor-Intensive, Simple Fix

A known problem most frequently found on early 6.4L engines (Job 1 engines built prior to August, 2007) entails the chafing of the high-pressure fuel pump’s wiring harness. Due to vibration, a hole is worn through the sheath of the wire and the bare wire touches the block, which grounds out the volume control circuit for the pump’s volume control solenoid. This leads to a loss of power or a no start condition and is accompanied by a check engine light and the truck's computer storing more than half a dozen DTC’s.

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Luckily, Ford offers an updated wiring harness that incorporates a mesh wire loom to protect the wires from wear (PN 8C3Z-9G805-A). While it’s a simple fix, it’s quite labor intensive being that the high-pressure fuel pump is buried at the rear of the engine, within the block. As stated earlier, this calls for the removal of the turbochargers, which may or may not warrant pulling the cab (depending on the preference of your technician).

Springing a Leak

Unlike the 6.0L, finding a puddle of coolant under a 6.4L typically isn’t indicative of blown head gaskets. However, it does usually signal that a radiator replacement is in store. The factory radiator is known to separate at the seams and leak (where the plastic end tanks meet the aluminum core).

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The updated version from Ford proved to be a bit more robust, but they can still fail. If you’re on the prowl for a used 6.4L, make sure you look for rust or white residue (from leaking coolant) along the sides of the radiator, from the top down to the tow hooks.

Spewing Soot

Cracked up-pipes, the plumbing that links the exhaust manifolds to the turbo, are extremely common on the 6.4L Power Stroke. Specifically, the pipes crack at the bellow (also referred to as the expansion joint or braided wire section).

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It’s believed that a lack of flexibility in the factory up-pipes, coupled with the movement of the engine, leads to eventual cracking. When this particular failure occurs, it’s accompanied by an audible hiss, a lack of power and a layer of soot coating the firewall, transmission and transmission tunnel.

Oil Dilution

Due to fuel being used during the regen process (i.e. cleaning of the DPF), the cylinders are often washed down with fuel, with some of it inevitably accumulating in the crankcase.

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This is why it’s so common for the 6.4L to gain a gallon of oil or more between oil changes. The extra oil is diesel fuel, and as you can imagine this doesn’t bode well for the main, rod and cam bearings (among other things) that rely on pure engine oil to keep them lubricated.

Writer's Tip: change your oil every 5,000 miles, not the 10,000-mile recommendation in your owner’s manual, and check the dipstick every other week.

Valvetrain Weaknesses

A major wear point in the 6.4L’s valvetrain lies in the lifters and rocker arms. Specifically, considerable wear occurs at the fulcrum ball of the rocker arms, along with the pressed-in ball on the rocker end of the pushrods.

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The reason for the wear stems from a lack of oiling issue, as the only lubrication the rocker arms receive comes by way of the pushrods. Beyond that, the rocker arms are also known to break when subjected to high-rpm scenarios where valve float occurs. Many enthusiasts invest in cryogenically treating the rockers to improve their durability.

Read about a Power Stroke engine that will cure your 6.4L blues – the 7.3L.

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