Have you ever wondered how fuel gets from the tank of a car to its engine? Well, for a diesel engine, it all starts with the lift pump, which is a low-pressure pump that draws the fuel up and out of the tank to provide a consistent, adequate flow of fuel into the fuel system. A fuel pump, on the other hand, is responsible for pumping the fuel into the fuel injectors.
Let's take a quick look at a typical diesel fuel system to see how it all plays out. Once the lift pump is activated, the fuel goes from the tank and passes through the primary fuel filter, also known as the pre-filter. This is designed to prevent relatively large particles, in the 10- to 15-micron range, from getting into the system. The lift-pump itself draws fuel through the prefilter, and from there the fuel goes through another secondary filter to remove yet smaller particles.
This more finely filtered fuel then finally arrives at the main, high-pressure fuel pump that sends it on to the injectors. These, in turn, spray the fuel into the cylinder heads under very controlled conditions, where it mixes with air for combustion. Needless to say, that means a bad lift pump can cause a cascade of other issues that can lead to serious problems with a diesel car or truck.
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A bad lift pump can begin causing problems as soon as you turn the key, since one of the first signs of impending failure is difficulty starting the engine since there may not be enough fuel available for combustion. In the extreme case, when the pump stops working entirely, the engine may be so starved for fuel that it won't start at all.
Even if a failing pump is working well enough to start the engine, it still may not deliver enough fuel for actual driving. The results in this case include the engine stalling, hesitating, and just generally suffering from poor performance. You may also hear a high-pitched whining or squealing of the lift pump struggling to do its job or notice white or black exhaust smoke, either of which can come from having not enough fuel and too much air in the cylinders during combustion.
Once a lift pump goes, the high-pressure fuel pump is put at risk. That's because it relies on diesel fuel for its lubrication and cooling, too, and without it, the high-pressure pump is likely to be damaged by increased friction and heat. It's a similar story with the fuel injectors, since they can see carbon buildups and physical damage from overheating when they're not cooled by the constant supply of diesel fuel from the lift pump.
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Following some smart tips for diesel maintenance can go a long way in keeping a vehicle healthy, and that's certainly true for diesel lift pumps. Perhaps the most important thing you can do is always change your fuel filters at the manufacturer's recommended intervals, always using OEM-approved filters. Don't forget to change water separators, either. They're engineered to filter water from diesel fuel, so if they're not maintained, it can get into the fuel system. The water not only causes corrosion but can also leads to some nasty microbes forming.
What happens is that the water and fuel can separate into distinct layers when sitting around in the fuel tank, and certain kinds of bacteria love living there. They rest in the water layer and essentially eat the hydrocarbons from the fuel layer. The stuff can grow large to be visible and, in fact, large enough to form clogs on your filters and damage the pumps.
Among the other ways to help keep your fuel pumps clean and working at their best is to use high-quality diesel fuel that you can trust to be free from major contaminants. The occasional fuel-tank cleaning will help your lift pumps keep lifting as well.
