Most of the evolution of the diesel engine has been driven by a need to extract more power out of the fuel. If we can extract more of the energy stored in the fuel, and use it more efficiently, then we can replace large engines with smaller ones that put out the same power, or we can make our large engines even faster and stronger! One of the biggest advancements towards efficiency came with the launch of High Pressure Common Rail Fuel Injection. I'm not going to bore you with the details but a pump sends fuel into a pipe (the rail) that all the injectors are attached to (its one common rail) and a computer controls the pump's output as well as the injection timing and duration of the injection based on all kinds of sensor inputs. So what's the really important stuff to know?
1) Water In Fuel (WIF). Water is the mortal enemy of all diesel injection components. Pumps, injectors, valves, every moving part in a diesel fuel system is lubricated by diesel (an oil). The moving parts in these items have very precise tolerances in order to handle the massive pressures (upwards of 30,000psi). Water doesn't make the best lubricant, so parts become damaged quickly. Diesel Fuel should be crystal clear. Any cloudiness indicates suspended water, do not add it to your fuel tank, do not start your engines, stop and play it safe. We've seen suspended water cost folks $30,000 before. Know what it is, and how to identify it. I like clear Racor bowls w/ heat shields and a flashlight, personally. Never add any liquid chemicals that claim to "remove water from fuel". There is a WIF sensor in the bottom of the on-engine fuel filter on the D4/D6. Buy an SLP spare from us to keep onboard with replacement filters. If you change the filter you have to transfer the sensor and they are often damaged during transfer. If you get the WIF alarm, find a safe place to anchor and shutdown that engine until you can address the water in fuel issue or confirm it's a faulty sensor.
Cloudy Diesel means suspended water contamination!
2) Raise Your Lubricity! The high pressure common rail (HPCR) system on the D4 & D6 engines was designed, developed, and tested in Europe. European diesel has a higher Lubricity standard than we do in the US, meaning the moving parts wear less over time in the higher grade fuel. When these high pressure fuel systems first came to the US we had terrible reliability issues. Early on, pumps and injectors were failing constantly and they're very expensive to replace because of their complexity. The European fuel system manufacturers begged the US to raise its Lubricity spec to meet that of Europe's. We met them half-way. People who think fuel additives are a waste of money rarely know about this fact. I personally like Diesel-Kleen, but anything that raises the Lubricity is a cheap investment compared to the price of injectors and pumps.
3) Treat the fuel system as a System, because it is. If one injector has a problem, they should all be tested. Don't just trust any fuel shop, find a fuel shop authorized by Bosch/Denso specifically for high pressure common rail. Send them the pump and injectors for testing and calibration. Any of those components could cost you an engine rebuild if they fail.
4) Read the article on here about the fuel cooler issue! Add replacement to your maintenance schedule.
5) The MPROP Valve. Mounted on your injection pump is a fuel meter valve. It controls the flow output of the pump. (Notice I said flow. Pumps produce flow... restrictions produce pressure). On a D4/D6 engine if we unplug the MPROP Valve the pump will go to maximum output. If you're experiencing certain symptoms it can be a good way to test if the mprop Valve has failed or the pump is weak.
6) Fuel Pre-Filter - What micron? You should have a 10 micron fuel/water separator plumbed into the fuel supply before the engine. Yes, a 30 micron will work in an emergency but just keep 10 micron spares onboard and you'll never have an emergency. I'm a big advocate of the Racor 900. Is it the best fuel filtration on the market? Nope, but its good enough and its so universal you'll never have to worry about finding a replacement regardless of what US marina you land at.
The fuel system on the D4/D6 can be a very reliable and easy to diagnose system if properly maintained. It can also be a very expensive system to repair/replace if you neglect it. Remember "clean fuel, clean fuel, and clean fuel" are the three most important things for any diesel engine. If you need help building a solid preventative maintenance program, give our team of experts a call.
