Common Rail Injector - Diesel World

The common rail injection system helped 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 an impressive little piece, with so many small moving parts that help maximize efficiency and atomization in the cylinders under each combustion cycle.


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.

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 started gaining in popularity as both a cleaner-burning tow rig and a full-blown competition hot rod.


With the armature and other internals removed from the bad injector, you can see that the corrosion just gets worse the further into it you get. Rust and pitting all along the inside of the injector and threads tell the story. Proper fuel filter changes, good clean fuel, fuel treatment, and even the addition of aftermarket fuel filtration systems are all great ways to combat these sorts of issues.

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, limited them. Lucky for us, the aftermarket has been able to capitalize on the new CP3. Common rail technology is being engineered and has 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-to-day 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.


Here you can see how effective the ultrasonic cleaner can be in bringing this internal pintle back to near-perfect condition. The pintle inside the injector is what moves up and down to control the injection event. As fuel rail pressure builds and the injector solenoid is signaled to move the armature, the pintle will move and allow fuel to run to the nozzle where it’ll be injected into the cylinders.

Most of the failures seen from the Cummins common rail platform comes from fuel contamination and a lack of overall vehicle maintenance. The factory injector has a great design, but due to extremely tight tolerances and 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 a no-start situation. Water and other contaminants in the fuel can lead to rust and corrosion problems that can cause sticking internals, meaning poor efficiency and continued running problems. Simple things like regular fuel filter changes, adding a quality fuel treatment, or even just buying fuel from the right place can really go a long way toward overall injector longevity. On some models, cracking of the injector body can also be an issue when running extreme rail pressures.

After receiving a set of core injectors to be rebuilt, there’s quite a few steps followed to ensure that a “like new” top-quality product is assembled and resold. Replacing the common failure items, cleaning everything in an ultrasonic cleaner, measuring tolerances, flow bench testing, and perfectly matched injection nozzles are all necessary to ensure you receive a completed set of injectors that can maximize efficiency, performance and drivability.

While a basic remanufacture to stock specifications is most common, Industrial Injection can also rebuild an injector to exceed factory performance with their extrude honed injection nozzles and other internal modifications. Using a state-of-the-art extrude hone machine, technicians can run brand new OEM Bosch injection nozzles through the honing process to enlarge the holes in the nozzle to improve fuel flow. There’s everything from a mild 50-hp nozzle that can improve a truck’s mileage, power, and streetability without putting undo stress on the powertrain to all-out, competition-only, 500+ horsepower nozzles for those wanting to make a statement on the sled pull or dragstrip. Over the course of the last year, with the help of a new in-house engine dyno, Industrial Injection has pushed multiple Cummins past 2,500 hp using their cutting-edge common rail Cobra injectors.


Industrial Injection’s common rail injector specialist Coy Larsen installs a completed set of 5.9L injectors into the test bench to check them for proper function and running condition. The flow bench is electronically controlled and uses a factory CP3 injection pump to give as close to an “in the truck” running test as possible. The test bench can check each injector and find any issues before they are sent out. If any injector is found to be outside the OEM specification, or just not balanced well with the rest of the set, the technician can remove it from the bench, adjust and re-test as needed.