TECH­NI­CAL DIS­CUS­SION

A LOOK AT COM­MON RAIL DIESEL IN­JEC­TION

Diesel World - - Contents -

The com­mon rail in­jec­tion sys­tem helped to rev­o­lu­tion­ize the light duty diesel mar­ket and not only brought about bet­ter emis­sions con­trol (OEM’S main goal) but also led to qui­eter run­ning en­gines due to higher in­jec­tion pres­sures—and, of course, bet­ter all-around per­for­mance. The com­mon rail in­jec­tor is a pretty im­pres­sive lit­tle piece, with so many small mov­ing parts that help max­i­mize ef­fi­ciency and at­om­iza­tion in the cylin­ders un­der each com­bus­tion cy­cle.

In the 2003 model year Dodge con­verted to the com­mon rail plat­form and said good­bye to the VP-44 in­jec­tion pump. At the time, the 12-valve Cum­mins and P7100 in­jec­tion pump was king of the horse­power wars and no one re­ally be­lieved in the po­ten­tial of the com­mon rail plat­form. But as time went on, a small few started push­ing the lim­its of the sys­tem—changes in in­jec­tion noz­zles, mod­i­fied CP3 in­jec­tion pumps and even dual CP3 pump kits be­came avail­able. As per­for­mance tun­ing started to im­prove, the com­mon rail Cum­mins re­ally started gain­ing in pop­u­lar­ity as both a cleaner­burn­ing tow rig and a full-blown com­pe­ti­tion hot rod.

In the be­gin­ning, com­mon rail in­jec­tors were needed to pro­duce 300-350 hp to meet the OEM needs for new light duty diesel trucks, and whether or not they knew there was more po­ten­tial in the in­jec­tor that’s kind of where they lim­ited them. Lucky for us the af­ter­mar­ket has been able to cap­i­tal­ize on the new CP3 and com­mon rail tech­nol­ogy and through the years has en­gi­neered and devel­oped in­jec­tors ca­pa­ble of 2,000+ horse­power to­day.

Coy Larsen, the in­jec­tor spe­cial­ist at In­dus­trial In­jec­tion, who has likely re­built more com­mon rail in­jec­tors than any­one in the coun­try, of­fered a lit­tle in­sight on what he deals with on a day-to­day ba­sis. Larsen has a deep knowl­edge of the in­ter­nal work­ings of the com­mon rail in­jec­tor and could prob­a­bly as­sem­ble one with his eyes closed. While in the shop with him we wanted to know what he sees fail most of­ten, what goes into re­build­ing an in­jec­tor and what im­prove­ments can be made to the fac­tory unit.

Most of the fail­ures seen from the Cum­mins com­mon rail plat­form comes from fuel contamination and lack of over­all ve­hi­cle main­te­nance. The fac­tory in­jec­tor has a great de­sign, but due to ex­tremely tight tol­er­ances and the 20,000+ fuel pres­sure go­ing through them even the small­est par­ti­cle of contamination can cause in­ter­nal cor­ro­sion and fail­ure in no time. Ero­sion of the ball seat in­side the in­jec­tor causes fuel to leak past it when closed, which causes a rough run­ning con­di­tion or even a nos­tart sit­u­a­tion. Wa­ter and other con­tam­i­nants in the fuel can lead

No­tice the rust spots devel­op­ing around the ar­ma­ture plate. This kind of wear would lead us to be­lieve that poor main­te­nance, wa­ter in the fuel or an­other form of fuel contamination and over­all ve­hi­cle ne­glect has caused this in­jec­tor to fail. This is a core that will not likely be saved.

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