There have been many generations of the 5.9L Dodge Cummins engine with varying fuel systems. The first two generations, spanning almost a decade (1989-1998), saw the rise of the 12-valve engine, which was excellent for high-performance applications. It was also fully mechanical, making it extremely reliable. Eventually, as emissions standards became stricter and the competition for the 12-valve engine heated up, we saw the advent of the 24-valve engine in 1998. This was a fully electronically controlled fuel injection system with better airflow, coolant flow, throttle response, and driveability. Dodge offered a few higher-powered versions of this engine, before releasing the ‘third generation’ of engines with the common rail fuel injection system. The common rail system offered consumers a huge increase in power and torque output, while simultaneously making the engine quieter, more efficient, and reducing emissions.

We will focus mainly on this last generation of engines and the fuel injectors that go in them. Although fuel injectors for the 5.9L can last upwards of a hundred thousand miles, they do fail at some point and when they do, they can cause massive damage to your engine if undetected or neglected. Moreover, it is critical that you find an appropriate replacement for your injectors. There are many options available on the market that will all offer different levels of performance. To make things easier, this article discusses diesel fuel injectors in greater detail to help you determine your replacement needs, and to help you go about this process efficiently.

 When should common rail injectors be replaced?

The average common rail injector will likely give you around 80,000 to 100,000 miles, although the Dodge Cummins 5.9L diesel injector is known to survive for more than double this number. As such, it can be slightly unpredictable how long your injector will last, making it important that you know what signs to look for so you can avoid damage to your engine. The quality and grade of Diesel #2 fuel may also highly influence the longevity of your fuel system durability. A common indicator of a failing diesel fuel injector is lower fuel efficiency. You’ll notice yourself making stops for fuel more often and might even see blue smoke emanating from the exhaust indicating injection out of specified time as a possible culprit.

Another sure-fire sign of a defective fuel injector is the smell of diesel from your exhaust. While many of us, especially diesel enthusiasts, love the smell of diesel, your exhaust should not be leaking this aroma (Excesses Nox and/or Carbon emissions) and it’s a possible sign that your injectors may require immediate attention.

Third, engine misfires can be an indicator that your injectors are struggling. However, this can be caused by several other factors too, such as low compression, a loose wire, etc., so it’s not always a clear sign, but when considered with other factors, it is very likely an indication of injector failure.

Fourth, the mixing of different fluids in the engine can point to injector problems. Engines tend to separate all the different liquids from each other. However, with a diesel engine, this can be tricky. For example, diesel fuel sometimes contaminates the oil in the crankcase when the injector is not functioning properly. This impacts the lubrication that the oil offers and results in various issues. If you notice fuel in your oil, this is a good sign that your injectors might need to be replaced.

Lastly, some other indications include increased emissions resulting from incomplete combustion of fuel, After treatment system failing such as SCR (Selective Reduction Catalyst) or DPF (Diesel Particulate Fliter), the check engine light being triggered, the revolutions per minute (RPM) needle on the tachometer might oscillate unpredictably, and keeping your vehicle in idle in traffic may make your car sputter, vibrate, or shake.

How to Diagnose Faulty Common Rail Injectors?

If you’ve been experiencing any of the aforementioned issues and want to know exactly what’s wrong with your injectors, you’ll need to know how to diagnose your common rail system and the injectors in it. Here is a step-by-step process that will help you address the problems you’ve been observing.

The first step towards diagnosing a faulty common rail injector is to investigate your vehicle’s on-board diagnostics (OBDII) system that tracks its performance. Invest in a good quality diagnostics tool, connect it to your vehicle, and let the tool do its magic. Once it finishes, it may give you trouble codes that will highlight specific issues with your engine that need attention. In case of trouble with your injectors, there will be a specific trouble code for the fuel injection system.

If the diagnostics tool returns these trouble codes, you’ll need to take the injectors out of the engine and check their performance. To make things simpler, you should send to a qualified and experienced diesel fuel injection specialist to properly test your injectors. Another source of problems could be nozzle erosion. This is when the nozzle of the fuel injector does not meet the original specifications it was designed for, ultimately leading to issues such as internal needle valve seat leaks. Nozzles used for injectors in common rail systems are highly susceptible to damage due to extreme and severe conditions including high fluid pressure, temperatures and mechanical extremes, and they need to meet strict requirements under these harsh conditions to perform optimally. If you’re attempting to rebuild your own injectors, replace both the nozzle and cap for better performance and peace of mind. However, this rebuilding process is better left to the professionals already in the industry with proper training, experience, tooling and equipment.

If neither of these issues seem to be causing your injector to fail, there might be an issue with other engine components such as the fuel pump. These can be checked with the help of another diagnostic tool that will record pressure from the pump and verify whether the number is appropriate for your specific application. Alternatively, consult a professional about your concerns and have an expert take a look. Issues like fuel contamination can also affect all your injectors, and you may need an expensive replacement set to fix the issue.

 Does a common rail diesel pump need to be timed?

No, a common rail diesel pump does not need to be timed with the engine. This debate, born of the results of differences between mechanical engines, similar to Dodge’s 12-valve engines, and electronically-controlled engines such as the 24-valve ones. In the former, the diesel pump did need to be timed with the engine to ensure precise injection of fuel into the cylinder after building up pressure, which then influences combustion of fuel and engine speed.

However, more modern diesel engines are electronically controlled as opposed to being purely mechanical, and the pressure pump’s regulation is controlled by the Electronic Control Module (ECM). The ECM is also responsible for firing the injectors properly, which it does based on signals and data from various sensors in the system. The ECM, along with the (FICM) Fuel Injection Control Module, together take care of precise injection of fuel into the cylinder.

Even though the pump does not need to be timed, you may still advance the Injection timing (within reason) to generate more power from your engine. Similarly, you can retard the timing for better fuel efficiency. The best way to do this is to program the ECM differently. No mechanical work needs to be done here. If the Injection pump is mechanical (the older 1st and 2nd  generations), you could also adjust the injection timing by rotating the pump in the engine. This can be done fairly easily but note that even a small change will result in a big timing change, so you should refrain from making any drastic changes or consult your diesel specialist.


Consider Dieselogic’s Diesel Fuel Injectors for the 5.9L

As we’ve discussed, there are several iterations of the 5.9L with various fuel systems and different parts to consider when looking for an injector that works with your engine. Additionally, investigating and diagnosing issues with the fuel injectors yourself can be tricky, and may increase your problems rather than fix them. As such, its best to consult a professional with adequate expertise with diesel engines so that you can have qualified advice and guidance with your vehicle.

We at Dieselogic have been in the Rebuilding and remanufacturing industry for over five decades now with several patents under our belt, giving us unparalleled experience when it comes to fuel injectors and diesel engines. Dieselogic offers three different injectors for the 5.9L that may be purchased based on which engine you have. All of these are manufactured-again grade injectors that have been inspected and thoroughly examined for any defects or deviance from OEM Bosch performance specifications. Components that have become worn out or are otherwise unable to produce high performance are replaced with new or manufactured-again parts and components.

Thus, you’ll get the performance of a brand-new injector for significantly less money. If this sounds like a good deal, call us today and find out more about our offer! We are confident that our prices are the best on the market, and if you discover a lower offer, we can discuss price matching as well.


Common rail fuel injectors can fail for a variety of reasons, and when they do, they can cause extensive damage to your engine through leakages, disturbed parts, just to name a few. As such, it is critical for vehicle owners to know how to spot and address potential issues with their injectors as early as possible. This article has discussed some warning signs that you may use to know when it may be time to replace your injectors, and how you can attempt to diagnose the issue. If you’re in the market for a replacement injector, consider Dieselogic’s offerings that are a product of over 50 years of experience and hard work. We offer Remanufactured / Manufactured-Again injectors at an affordable price but without compromising on quality. To find out more about us and our injectors, call us today!