All Cummins ISX engines have the XPI common-rail injection system, which uses a crankshaft-driven pump to keep the fuel rail – seen of the left side of this 11.9L ISX – pressurized to more than 30,000 psi, providing full injection pressure to solenoid-activated injection nozzles in the head. Such systems provide maximum injection pressure even at low rpm and eliminate the need to adjust the injector rockers when doing overheads.

The clearances inside diesel injection system parts are closer than those found in any other technology. The plungers and needle valves in injectors need to fit tightly to ensure precise metering and avoid wasting energy in generating extremely high fuel pressures in excess of 30,000 psi.

While the new common-rail designs shun unit injectors in favor of a high-pressure pump and injection nozzles with on-off valves, the clearances in the pump and inside the nozzles are just as tight for the same reasons. “A single fingerprint on the XPI injector plunger will bind the injector to prevent injection sequence,” says Zack Ellison, Cummins’ director of customer technical support.

As emissions standards have gotten tighter, the already tiny holes in injection nozzles have gotten smaller to increase injection pressures. Research has shown that the tinier the holes and the higher the pressure, the less soot the engine will produce – and the better it will perform.

Tinier working spaces also mean that fuel must remain dry. Water not only can wash lubricating fuel off hard-working injector parts, its different flow characteristics also can blow the tip off an injector.

Use a primary filter that includes water separation capability (which means specially treated paper that keeps water from passing through), a reservoir to catch water and a drain, says Paul Bandoly, Wix Filters’ manager of technical services and customer training.

Most of Detroit Diesel’s engines are equipped with a Davco primary filter and water separator. “Not all primary filters have water drains,” says Scott Faris, technical service manager. Those that do have drains – which typically are called primary water/fuel separators – should have 93 percent minimum efficiency on emulsified water. “They should be drained daily, which is easy to do since most have a handy valve on the bottom of the filter.” All Series 60 engines built after January 2004 come with a water separator system. “It’s also essential to drain fuel tanks monthly, and never right after refueling,” Faris says.

Most engine makers specify an initial setting of overheads early in an engine’s life, just after it breaks in and settles down.

All DD15 filters should be changed at 50,000 miles, and a Davco filter allows change intervals to be extended to beyond 100,000 miles depending on fuel quality, says Brad Williamson, Detroit Diesel’s Powertrain communications manager. The filter assembly has a water-in-fuel indicator that a driver can check during a routine walkaround.