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DEF vs. Diesel Fuel

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Have you ever wondered what happens when a diesel fuel system is contaminated with diesel exhaust fluid? The damage occurs quickly and can be extensive! Diesel Exhaust Fluid or DEF, is a solution of 32.5% high purity urea and 67.5% deionized water used in the selective catalyst reduction system SCR to reduce NOx emissions. The fluid is very corrosive and it's affect on fuel system components is devastating: premature high pressure pump and fuel injector wear, debris, pitting/corrosion, distortion of materials, plugged fuel injector return line.

The images in this article are of a 2011 F350 equipped with a 6.7L Power Stroke diesel engine that had an unknown amount of DEF poured into the fuel tank by accident and the truck was driven. The high pressure fuel pump actually seized while the engine was running subsequently cracking the HPFP housing in the process. As a result the HPFP drive gear which is driven by the camshaft gear sheered the key and spun on the shaft. Unfortunately the crankshaft drive gear which is shrink-fitted onto the crankshaft also spun when the pump locked up affecting base engine timing. At this point the engine was headed for total failure with the crankshaft and camshaft now effectively un-timed. Piston to valve contact rendered the cylinder heads, all 8 pistons, half of the 32 push rods bent and several rocker arm carriers broken and unserviceable.

Let's take a closer look:

Left, one of the first things is to take fuel samples from the fuel conditioning module and at the engine. This fitting was disconnected from the engine mounted fuel filter and given time to allow for the creation urea crystals. On the right is the primary fuel filter that was removed also to check for the presence of DEF. The resulting crystals are the proof of DEF contamination of the fuel system.




The next two things a technician should remove and inspect are the fuel pressure regulator and volume control valves. These also need to be given time to allow crystals to form and also to inspect them for signs of corrosion and rust which also can identify water contamination as well. Here both components have developed some significant crystal growth over several days verifying that the DEF had indeed made it's way into the engine's high pressure fuel system.




Here is the seized Bosch 4000 high pressure fuel pump. Internal damage caused it to lock up. The torque from the running engine split the case. Note the DEF crystals in the crack. On the right is the front gear train with the large camshaft gear on the top and the crankshaft gear below with the red arrow pointing to it. This is the gear that is shrink fit onto the crankshaft that moved when the HPFP locked up. The pump is mounted on the top front of the engine and driven by the camshaft gear. (It is not shown in the image)




With the engine un-timed the pistons contacted some of the valve. On the left are some bent push rods. The force of that contact was also enough to break a few of the valve rocker carriers. Each cylinder has one carrier assembly for all four rocker arms and the assembly on the right is broken in two.



Edited by webmaster

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