One reason the Sprinter’s 2.7 fuel system is susceptible to airlock is the fuel pump’s high location on the engine. (See the picture to the left.) The location makes for great access and maintenance, but it is bad news when changing the fuel filter or you run out of fuel – gravity takes over and the pump drains. (Because of the low surface tension of diesel, the vacuum of the closed system does not hold long in the presence of air.) The pump also does not have good self-priming capabilities. But this may not be unique to the Mercedes 2.7. At the time of my experience with this problem, there was no readily accessible and affordable maintenance manual for the Sprinter in the US.1 Here is the benefit of my experience. Before proceeding, it seems advisable that you should be fairly certain as to the source of the air in the system. If the air did not come from running your tank dry2 or from other maintenance on the fuel system, it seems advisable to do further investigation to find the source of the air before proceeding with the following steps. Follow my example at your own risk.Check to see if there is air in the lines. Lucky for us Sprinter owners, the feed line from the fuel filter to the fuel pump and the line from the fuel pump to the next step of the injector process are transparent, accessible and visible. (In the picture feed line is visible under the blue line and the black vacuum hose.) If there is air in the lines, you should be able to see bubbles and/or foam in either line shortly after an attempted start. And those bubbles will be moving up to.
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