Why Fuel Injectors in Post-Common-Rail Diesels Fail

Diesel fuel injectors typically fail due to either the lack of mechanical soundness of the injector structure or the quality of the fuel that consistently runs through the injector. By understanding the inner workings of a fuel injector, we can better understand what makes them stop working and, more importantly, how to prevent it from happening.

Increased Risk to Modern Diesel Fuel Injectors

By following a consistent maintenance program and avoiding bad habits (i.e., filling up with bad fuel), you’re highly likely to drive thousands of miles without any trouble. Older diesel fuel injection systems use about half of the fuel pressure that modern-day diesel engines use and push the fuel through significantly larger passageways. To be more precise, modern common-rail injectors typically fire two or three times each engine cycle. The increased pressure doubles or triples the wear and tear on the fuel injection system.

Mechanical Problems and Failures

There are five common types of fuel injector failures. Let’s go over what these failures are, symptoms of the problems, the causes, and how to prevent them.

Failure #1: No Injection

Symptoms:

• High (positive) balance rates, which signify that fuel is being added to the cylinder because the computer thinks the fuel injector’s flow is inadequate
• Low cylinder contribution (can be tested by turning off one injector at a time and watching for a drop in engine RPM)
• Engine control unit (ECU) fault codes

Causes:

• Rust or debris clogging the nozzle
• Loss of cylinder compression
• Armature (rotating coils) and/or needle stuck
• In rare cases, a bad stator

Prevention:

• Change filters as recommended
• Maintain a clean fuel system
• Only buy fuel from reliable sources
• Use only components that are specifically designed or manufactured for your system
• Do not tie the returns from multiple high-pressure pump kits and injectors to a single return line (can lift or even blow off the injector stators, which will shut the injector down)
• Do not store your vehicle for an extended period of time without starting it and putting diesel stabilizers in your tank

Failure #2: Too Much Injection

Symptoms:

• Poor running
• Excessive smoke when idling
• Banging sound
• Excessive exhaust gas temperature
• High balance rates, which indicates that the computer is removing fuel from the injector
• Engine damage due to excessive heat or hydraulic lock

Causes:

• Debris in the injector’s control system and holding it open
• Debris in nozzle needle seat and holding it open
• Cracked nozzle caused by excessive pressure
• Overheated nozzle (typically due to an injector being improperly installed)
• Worn ball seat in injector

Prevention:

• Replace worn and high-mileage injectors as soon as possible
• Replace nozzles regularly
• Change fuel filters regularly
• Maintain a clean fuel system
• Only buy fuel from reputable sources
• Only use parts that are specifically designed for your engine

Failure #3: Improper Fuel Injection Rate

Symptoms:

• Rough running
• Poor cylinder balance
• Significant variation in exhaust temperature from cylinder to cylinder

Causes:

• Clogged nozzle
• Poor nozzle flow balance
• Improper nozzle needle lift (often due to incorrect or missing parts)
• Wire-brushed nozzles

Prevention:

• Have injectors serviced and tested by a reputable source
• Purchase injectors from a reputable source
• Maintain a clean fuel system
• Only buy fuel from reputable sources
• Only use parts that are specifically designed for your engine
• Never clean your nozzles with a wire brush

Failure #4: Incorrect Injection Timing and Duration

Symptoms:

• Rough running
• Knocking
• Poor cylinder balance
• Significant variation in exhaust temperature from cylinder to cylinder

Causes:

• Improperly assembled injector
• Missing or incorrect parts
• Worn ball seat

Prevention:

• Replace worn or damaged injectors
• Have injectors serviced and tested by a reputable source
• Purchase injectors from a reputable source

Failure #5: High Internal Leakage or Return Flow

Symptoms:

• The engine doesn’t start easily and requires increased cranking time to do so
• Low common-rail pressure codes

Causes:

• Cracked injector body or nozzle body
• Worn injector ball seat
• Blown internal high-pressure seal
• Inadequate clearance for the nozzle needle
• Leaking cross-feed tubes (seen in Cummins)

Prevention:

• Change fuel filters regularly
• Maintain a clean fuel system
• Only buy fuel from reputable sources
• Prevent increasing rail-pressure and injector pulse widths when tuning
• Avoid using remanufactured or aftermarket parts, and only use injection components that are specifically designed for your system
• Never mix nozzle needles, as they are matched to the injector body and moving one from another can lead to an improper amount of clearance or needle lift

While there are other potential problems, mechanical and otherwise, that can indicate or cause any of these problems, the indicators and causes listed have been found to be the most likely.

Injection Failures Due to Poor Diesel Fuel Quality

Low-quality fuel can be a major source of problems for any engine, and a diesel engine is no exception. There are three fuel injector problems that are generally caused by bad fuel, including excessive wear, abrasion, and unwanted deposits. Let’s discuss these common problems in greater detail.

Failure #1: Excessive Wear

Excessive wear can occur and affect any injector over a long period of time, but the type of fuel you use has a huge impact on the amount of wear your injector experiences. Sulfur was used as a natural lubricant in crude oils, but was eventually found to ruin diesel particulate filters. Over the years, sulfur levels were significantly reduced and diesel refineries began putting additives in the fuel to restore the lubricity. So, by using the new ultra-low-sulfur diesel (ULSD), you can limit the wear on your fuel injector.

Failure #2: Abrasion

Abrasion is typically caused by impurities in fuel and can lead to premature injection failure. These impurities can be found in even the best diesel fuels and are able to pass through even the tightest onboard vehicle filters. The more of these particles there are within fuel, the more they will cause abrasion to the injectors as they pass through. Fortunately, with proper maintenance by fuel suppliers and quality fuel filters, the damage caused by abrasion can be limited.

Failure #3: Deposits

Excessive deposit buildups, both internal and external, are the reason for most injector failures. These deposits can disrupt the fuel spray, which causes inefficient fuel combustion. This problem is evident if you notice a noticeable loss in engine power or fuel economy. Additives are available that have been found to control any deposits that may occur.

Conclusion

Much can go wrong with a diesel fuel injector, but, if your system is mechanically sound and you’re diligent about the fuel you fill your vehicle with, you should enjoy many miles without interruption.