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CR Fuel System Replacement: The Total Failure Mode

Gear case (3)It has become common knowledge in the industry that some CR common rail diesels experience injection system failure and complete fuel system replacement. Hopefully if that happens, your engine is still in warranty and the dealer will perform that job for free. Because it can cost close to $Ten Grand! When your CR Tdi stops running, and has a high pressure system pressure diagnostic trouble code (DTC), then metal flakes are found inside your fuel filter, the jig is up. At the dealer, the entire fuel system gets replaced: the tank, electric transfer fuel pump in the tank, auxiliary fuel pump, high pressure fuel pump, the fuel rail, high fuel pressure regulator, fuel pressure sensor, the pressure retention valve, the fuel temperature sensor, all four injectors and fuel pipes, and all the fuel hoses. And a fuel filter.

First, understand that these cars essentially have three fuel pumps. There is an electric transfer pump in the tank to provide the initial fuel flow. An electric auxiliary pump sits out beside the engine, and it feeds a higher pressure to the main pump. The main pump is driven off the timing belt, and it directly feeds the injectors through the common rail pipes, hence the moniker “Common Rail” or CR diesel. The main pump is also known as a High Pressure Fuel Pump or HPFP. The fuel filter is located after the transfer pump, and before the auxiliary pump, meaning any metal flake coming from the auxiliary pump is going straight to the HPFP. There is a screen, but that just stops large particles, and won’t save the HPFP in the case of auxiliary pump failure.

There seem to be three possibilities for failure modes. One is when the auxiliary fuel pump grinds up, sending metal flake into the main pump, which makes it fail. This could be caused by transfer pump failure, meaning the auxiliary pump is having to suck the fuel from the tank, and will cavitate. The next mode is when the auxiliary electric fuel pump fails first, and it starves the high pressure pump driven by the timing belt. The high pressure pump may then cavitate, as it is built to push fuel, not suck fuel. Cavitation makes bubbles which are actually vacuum pockets that fill with the vapor of the fluid. Extreme cavitation causes the high pressure pump to grind up, shedding metal flake into the injectors and the rest of the system. Cavitation can make bubbles at faster than the speed of sound, which can rip metal off the surface. Ever see a boat propeller that looks like it was blasted with a shotgun? The same thing can happen to your high pressure fuel pump. Karmakanix checks the in-tank electric transfer fuel pump every time we replace a fuel filter on a CR or PD diesel Volkswagen or Audi. The in-tank transfer fuel pump can be checked anytime in a matter of minutes. The auxiliary electric fuel pump can be checked within a half an hour. With the older PD diesel cars, customers could barely hear the electric fuel pump. In the CR diesels, the improved pumps are silent. But when they are perfectly silent, that can wreck your entire fuel system. You are in for complete fuel system replacement.

The third mode comes from improper procedure when changing a fuel filter. Two possibilities exist than can result in main pump failure. A tiny amount of metal flake in the filter is normal. Major amounts either precede or accompany fuel system failure. When the filter cartridge is removed, some of the metal flake previously caught by the filter element will mix toward the center of the housing, and it must be completely evacuated. Else, when the new filter is installed, that metal flake will now be in the center and will go straight to the main pump. The other scenario involves air trapped but not bled out completely. Any air will damage the main pump, and the bleeding procedure should be followed to a Tee and then repeated. And after initial startup, the engine should be left for at least 5 minutes at an idle.

So far, all of the complete fuel system replacements caused by transfer pump and auxiliary pump failures in CR Tdi cars that we have seen at Karmakanix have been in the 2009 and 2010 model years. We do not know if those are just the first of a wave, or if there is some inherent issue with just the early system. Karmakanix has a policy of checking the transfer pump at every service that includes a filter change. We do not want to see VW and Audi Tdi owners suffer huge repair bills for fuel system replacement that may eventually exceed the value of the car. So far, the vast majority of the cars afflicted with total fuel system failure have been covered by factory. That will obviously change as the cars get older.

The National Highway Traffic Safety Administration conducted an investigation into a number of cases of high pressure fuel pump failure. The original report from VW to the NHTSA can be found at: National Highway Traffic Safety Administration PE10034. Skip down to page 22 for an explanation of the system. On page 30 starts the meat of the findings. The Office of Defects Investigation (ODI) conducted a five year research and engineering analysis of the HPFP failure in Volkswagen and Audi Common Rail Injection Tdi vehicles. The ODI Engineering Analysis Closing Report from March of 2015 is worth a browse. It has been widely and mildly misquoted, construed as pointing the finger at the driver. In fact it shows that the early CR Tdi had some iffy engineering that was improved, and “misfueling” only accounts for less than half of those failures. Misfueling is poorly understood to indicate adding gasoline to the fuel tank. In fact Volkswagen defines “Misfueling” as adding any inappropriate or contaminated fuel, including water content, rust, biodiesel in excess of 5%, microbes and debris.

What To Do If You Put Gasoline In Your Tdi Diesel Vehicle

You may see your Check Engine Light come on and/or blink, and maybe the glow plug light as well. Perhaps you might notice something different about how the engine runs or sounds. You may just remember grabbing the wrong pump that did NOT have a green handle, or smell a faint gasoline smell. First and foremost: STOP DRIVING!!. Your car needs to be towed. Just that last couple of miles to get home or to work can cost you close to ten thousand dollars! There is a Factory Service Bulletin on purging incorrect fuel from a Common Rail system. And at Karmakanix, we do the purge sequence twice. We realize that the fuel sender / transfer pump assembly in the tank has a small reservoir that needs to be pumped out twice, so we add 1 gallon of diesel to the pumped out empty tank and bleed that through the system. We then purge that gallon out before we change the fuel filter and then perform the regular purge sequence. We check for possible metal flake that might indicate possible or eminent failure. We also add an entire bottle of Stanadyne fuel additive to increase lubricity to make up for the trace amounts of gasoline still present in the system. After repeating the bleeding procedure at least three times, we let the engine idle for half an hour before a test drive. And we highly suggest that one immediately fills the tank completely with fresh diesel fuel.

It is a common misconception that Winterized Diesel Fuel contains gasoline, because that’s how it was in the middle of the last century. Times have changed. Modern fuel systems, especially Common Rail, cannot withstand ANY gasoline in their systems. Nor is there any kerosene. Winterized Diesel Fuel now has some mixture of a refined version of kerosene suitable for injection, and secret additives that the fuel companies talk about, but won’t disclose. Tech talk indicates that the enhanced explosion from a gasoline mixture can damage injectors, and we know that any reduced lubricity will endanger your High Pressure Fuel Pump.

A Possible Way to Avoid Complete CR Fuel System Replacement

Really it would seem obvious that lubrication is key to making all the fuel system components not fail. The issue of failing pumps causing metal flake is primarily one of lubricity, and since the advent of ULSD fuel, lubricity has been the top topic. Karmakanix recommends using a fuel additive with every tank. At a cost of about $2 per tank, it is cheap insurance against possible expensive repairs. Stanadyne is proven to inhibit wear, keep systems clean, lower soot production and increase mileage. Lower soot production will of course increase the life of the Diesel Particulate Filter (DPF) as it captures soot and burns it down to ash during regeneration. The DPF has a maximum ash load of 45 grams before it requires replacement. The other two additives that we know and trust are Redline and Amsoil. It is not just good advice to use additives, it is essential advice if one wishes to keep their Tdi for the long haul.

Gear case (3)