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6.4L Problems

The Bad Side and the Ugly Side of a Good Engine

Mike McGlothlin
Dec 1, 2012
Photographers: Mike McGlothlin
In the wake of all the catastrophic failures associated with the 6.0L Power Stroke, the 6.4L had a lot to live up to when it was introduced for the ’08 model year. For the most part, it has. The 6.4L’s EGR, turbocharger(s), and fuel system issues are far less common, and larger-diameter head bolts keep the heads secured to the block much more effectively. Although select engine failures occur here and there, the 6.4L has a pretty good track record so far.
Photo 2/12   |   6 4l Problems 6 4l Power Stroke
While a lot of the ’08 to ’10 Power Stroke’s problems pale in comparison to the 6.0L’s, they still have their own unique sets of issues and weaknesses. Some are emissions related, several are amplified with aftermarket add-ons, and a few, unfortunately, are just the nature of the beast. Follow along as we highlight the biggest problems (and fixes) that come with 6.4L ownership.

Oil Dilution

One negative habit of the 6.4L is its ability to make oil. That is to say fuel slips past the piston rings and accumulates in the crankcase. It’s especially common in DPF-equipped trucks that see more regeneration cycles. Remember, the 6.4L’s regeneration cycle uses a post-injection event to introduce extra fuel during the exhaust stroke. In a perfect world, 100 percent of that fuel vaporizes and travels downstream to the catalyst (which serves as an incinerator for accumulated soot). But in reality, not all fuel vaporizes during the post-injection event, and the leftover fuel latches onto cylinder walls and squeezes past the piston and rings, and into the crankcase. We know one 6.4L owner who drained 6 gallons (24 quarts) of oil during an oil change—3¾ gallons (15 quarts) would’ve been normal. That’s nearly a 60/40 mix of oil to fuel circulating throughout the engine.

Three Reasons Oil Dilution is Worrisome

The more diluted your engine oil is with diesel fuel, the less lubricity all bearings and bottom-end components see.
You run the risk of eventually hydro-locking the engine (if neglected long enough).
Elevated oil levels can spell disaster for any diesel engine, especially if it slips past piston rings and finds its way into a cylinder during the compression stroke. This can lead to a runaway situation (it’s rare—but it happens).

What You Can Do to Avoid it:

Keep an eye on your dipstick (check your oil level once a week).
Observe a 5,000-mile oil change interval as opposed to Ford’s 10,000-mile recommendation.

HPFP Issues:

Chafed wires in the high-pressure fuel pump cover gasket (arrow) are common on ’08 engines built before August 20, 2007. The unprotected wires (which are part of the high-pressure fuel pump cover gasket) rub on the pump and eventually a hole wears through the sheath, causing the bare wire to touch the block. This grounds out the volume control circuit for the volume control solenoid, a slew of fuel-related codes are thrown (P0003, P0004, P0091), and you’ll experience low power or a no-start scenario. Other codes thrown can include a P042F, P0488, P0670, P0691, and P179A. This is because the same fuse that blows from the short in the high-pressure fuel pump circuit is used for EGR components, the glow plug control module, the electronic fan clutch, and the VGT actuator. In December 2007, Ford issued a TSB for this issue (TSB number: 07-26-2) and then released an updated wiring harness for the high-pressure fuel pump. The updated harness simply uses a mesh wire loom to protect the previously exposed wires from rubbing on the block or pump (PN 8C3Z-9G805-A). The updated wiring harness is said to exist on all engines built after August 20, 2007.
Photo 3/12   |   6 4l Problems chaffed Hpfp Wire
An ill-fated DTC is a P0088, which usually means the fuel pressure control valve within the high-pressure fuel pump is sticking. The code gets thrown due to rail pressure being too high, and the controller not being able to regulate it properly. Because the pressure control valve cannot be rebuilt or replaced, it calls for a brand-new high-pressure fuel pump.
Water In Fuel
One of the 6.4L’s biggest problems lies in its water separator, and water contaminating the fuel system. According to the Diesel Technician Society, fuel coagulation often occurs in the collection bowl. The reaction between water and fuel forms a white, greasy substance, and the buildup eventually blocks the drain valve ports. This keeps water from being removed from the system when you attempt to drain it. And because the buildup shrinks water collection capacity, water eventually passes on to the fuel system. After that, water reacts with the metal in the injection system components to form rust. Rust is behind a lot of injection pump, injector, and even some complete engine failures in ’08 to ’10 Super Duty trucks.
Photo 4/12   |   6 4l Problems water Septerator
You can stay on top of this by regularly opening the water separator valve (along the framerail) and allowing it to drain (do this once a month). You can also periodically remove the water separator’s manifold cover (arrow) and manually clean out the buildup by hand (brake cleaner is safe to use). Also, make sure you keep up with Ford’s recommended 20,000-mile fuel filter change interval.
Photo 5/12   |   As previously mentioned, keeping rust out of the 6.4L’s fuel system is a big deal. To keep the Siemens K16 high-pressure fuel pump in tiptop shape and the rest of your fuel system happy, run a fuel additive that guards against the formation of corrosion and rust. We would choose a reputable, alcohol-free additive that helps remove water from fuel, and use it at every fill up.

White Smoke, Loss of Power

The factory, hot-side intercooler boot (driver side) is known to hold moisture and cause white exhaust smoke intermittently, and in wet weather. Ford issued a technical service bulletin for the problem in February 2011 (TSB number: 11-2-2). White and gray smoke scenarios are most common when engines are routinely used for short trips during which the engine never reaches operating temp and very low boost levels are seen. Over time, condensation builds up in the hot-side boot. Then, once the driver decides to take a longer trip (during which the engine reaches operating temp) and is more aggressive with the throttle, the increased boost forces the moisture through the intercooler and into the engine. The result is white and gray smoke out the tailpipe and power cutting out.
Photo 6/12   |   6 4l Problems intercooler Boot

Less Frequent (Yet Notable) Problems

Rocker arms can break under high horsepower and are known to wear severely at the fulcrum ball (age and high mileage seems to cause failure in stock applications, in which the ends wear down due to friction).
Lift pumps can fail prematurely (it’s not just a high-mileage problem) in stock or modified trucks (although tuned engines can kill them faster, as the pump struggles to maintain fuel supply to the injection pump).
All 6.4Ls seem to have considerable blow-by (even 100 percent healthy engines), possibly due to relatively loose ring end gap specs from the factory.
Injector O-ring failure is somewhat common with age.
Catastrophic injector failures aren’t particularly common, but some failing units can stick open, causing oil dilution, and in some cases cause piston damage or even hydro-lock the engine.
Oil coking can plug turbo oil drains in some instances, leading to premature turbo failure.

Tip of the Month (for utility and service truck owners)

We’ve heard horror stories of fleet owners stretching oil change intervals an extra month or a few thousand more miles—and paying a hefty price for it. Remember, the industry standard is 1 hour of idle time = 25 miles driven. So a truck idling 10 hours a day, five days a week needs fresh oil every month, not every three…


Elite Diesel Engineering
Pueblo West, CO 81007
Flynn's Shop
Alexander, IL
Randall's Performance and Accessory
Gladstone, IL 61437
River City Diesels
East Peoria, IL 61611
Diesel Technician Society