The first step to determine...
The first step to determine a diesel injector nozzle's condition is to test the nozzle opening pressure (NOP) and spray pattern in a special fixture. A hand-operated hydraulic pump creates the NOP. The nozzle is sprayed into a chamber that features a fan to remove fumes. Calibration fluid with the same specific gravity of diesel fuel is used.
Your diesel engine injector nozzles are responsible for delivering the proper amount of fuel to each cylinder bore for the load and horsepower demand. Over the course of the life of the engine, the number of injection events can reach the billions, and possibly trillions. In addition, the injector nozzles are subjected to an extremely abusive environment-more than any other part of the engine. The nozzles live in the diesel engine's combustion chamber and are exposed to temperature peaks of more than 1,800 degrees, while the internal pressure may exceed 30,000 psi.
Though almost every fuel system manufacturer recommends servicing the nozzles, these procedures are often neglected by the engine owner and only addressed when a problem exists. Preventive maintenance should be part of every diesel engine owner's plan if long life and trouble-free performance is desired.
Injection Experts
To expose Diesel Power readers to the steps required to service mechanical injector nozzles, we visited with Mack Boring & Parts Company in Union, New Jersey. Having no association with Mack Trucks, Mack Boring not only sells brand-new diesel engines, it also rebuilds diesel engines and offers complete fuel system service for most diesel applications.
The Mack Boring & Parts Company's fuel system shop senior technician is Frank Pakay. He is part of Mack Boring's service department, managed by Mike Alfano, where diesel nozzles and injection pumps are serviced for customers around the country as a result of the shop's reputation and long history of working with only diesel engines.
While Diesel Power was at Mack Boring, a set of multi-orifice injectors was being prepared for service. They were from a 440hp Yanmar 6LY2A-STP turbocharged six-cylinder marine engine. The customer's complaint that prompted the injectors to be removed was a report of blue/black smoke at idle. Other common issues that often point to the need for injector service are a rough idle or misfire, excessive fuel consumption, hard starting, and a general lack of performance. Though the Yanmar engine uses its own design of nozzle, it is very similar to what would be found in a Cummins engine with a mechanical fuel system.
 The injector assembly is placed...  The injector assembly is placed in a vise and the cap nut is removed. |  The nozzle assembly then lifts...  The nozzle assembly then lifts up from the case. |  The pintle (or in the case...  The pintle (or in the case of this Yanmar injector, the needle) is removed. The nozzle body and components are mated and should never be separated. |