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Ford’s 6.7 Diesel Fuel System
The 6.7 diesel has now been out long enough for independent shops to begin seeing these vehicles come out of warranty. Since this is an all new engine design and there are several new systems on this engine, it is a good time to begin going over some of them. This article will focus on the fuel system.
The 6.7 diesel incorporates a low pressure fuel pump located on the frame rail under the driver’s seat. This pump will produce 48 to 58 PSI of pressure if it is functioning correctly. Ford incorporated a low pressure switch on this engine to tell the computer if the low pressure fuel pump is producing sufficient fuel pressure. If it is not, it will disable the engine from starting and in some cases prevent the engine from even cranking over to protect the high pressure pump from damage (Figure 1). Click Figure 1 below to enlarge.
Figure 1
Figure 1
It is important to note that the low pressure system has a filter housing just like the 7.3L and 6.0L diesels did. When this filter is replaced, the system needs to be bled before attempting to start the engine. In most cases this procedure is simple: turn the key on for 30 seconds, letting the pump run; then shut the key off. Repeat 3 or 4 times. The system should bleed itself during this time. It is also important to note that any debris on the filter can spell disaster for the pump and injectors. Ford has released TSB #11-10-10 on this concern, and has included a photo of the filter and an explanation of the repair. I have received many calls regarding this issue. It is very important to replace the fuel pump and injectors, along with new filters and a complete fuel system flush. The upper fuel filter housing is replaced as an assembly and is not to be taken apart. Though there are three ports on the original filter assembly, the third port has no useful purpose. When a new filter is installed it will only have two ports.
This fuel system also incorporates a pressure and volume control solenoid. The volume control valve is mounted on the high pressure pump. The pressure control valve is mounted on the back of the driver’s side fuel rail. You will also notice the fuel pressure sensor is mounted at the front of the driver’s side fuel rail. The computer uses the volume and pressure control valve to more accurately control fuel pressure during acceleration and deceleration. It should be noted that after a battery disconnect or a PCM reflash, the computer needs to relearn the correct duty cycle for the solenoids. We have experienced some issues with the driver’s side fuel rail. In these cases the entire rail was replaced to fix the concerns.
The high pressure fuel pump is mounted in the front of the engine instead of the rear. This pump has pressures similar to the 6.4L diesel; it takes around 5,000 PSI of pressure to start the engine. When installing a new pump, the unique feature is a timing procedure (Figure 2). Currently there have been very few concerns noted with this pump. If a pump is replaced several relearn procedures need to be done using a factory or equivalent scan tool. You will find fuel system reset procedures in the scan tool. This procedure will be under the ‘powertrain’ section of the factory scan tools, under the ‘function tests’ of Snap-on scan tools, and under the ‘special functions’ of OTC scan tools. Click Figure 2 below to enlarge.
Figure 2
DS_Fig2
Since the fuel injectors on this engine are mounted externally there is no need to remove the valve covers to access or repair the injectors. It is important to note that the steel line going to the injector from the fuel rail is a one-time use only. Once this line is loosened it will need to be replaced. It is also important to note that these injectors have specific programming to the PCM. If an injector is replaced, it has to be programmed into the PCM or driveability concerns will result.
So far this engine’s fuel system hasn’t had a lot of problems unless the fuel is contaminated. We have seen very few injector and/or pump problems; however, we have seen several issues if the customer puts reductant fluid (diesel exhaust fluid) in the diesel fuel tank by mistake. This will usually damage the entire fuel system.
