What Are the 5.9 Cummins Bad Injector Symptoms? (Get Stunning Solutions!)

Determining 5.9 Cummins bad injector symptoms can be confusing as they seem like other non-serious vehicle issues. Thus, by reading this article you will get a clear idea of what are the exact signs to look for. Let us begin.

That satisfying sound of a 5.9 Cummins diesel engine running smoothly on the road is one of the favorites of auto lovers.

But, when instead of this sound, misfiring and rough idle noises are more noticeable; this indicates something wrong has happened with the vehicle’s injectors.

Set of fuel injectors have been the main players in the system of 5.9 Cummins. These injector pieces ensure that the diesel engine is getting the required fuel amount at that moment.

They carry the fuel smoothly into the cylinders. Thus, injectors going bad is a big concern. Different engine models have different variations and complexities in this part.

“Typically, symptoms like the excessive blow of smoke, Rough idle, power loss, high-return fuel, and the vehicle not starting at all directly indicate one or more bad injectors.”

However, 5.9 Cummins engines are well-recognized for their excellent power and durability.

But, again, it is also possible for even the best diesel engines to develop issues like 5.9 Cummins bad injector issues occasionally.

Bad injectors are one frequent problem among these which results in the rise of many other vehicle-related issues.

So, allow us to share an informative article on the obvious signs and symptoms of bad diesel injectors and their solutions.

Can You Drive Diesel With a Bad Injector?

Yes, it is possible to drive when the injector has gone bad. This is okay to do only for short distances and periods as prolonged uses can raise severe issues in the vehicle.

Having faulty injectors, regardless of them being just one or more, need proper treatment right away after being detected.

With a bad injector, the possibility of arising electrical or mechanical issues or wear gets higher.

Aside from this, multiple unpleasant problems take place, such as your vehicle not being able to start or beginning to stall.

Other rare issues like engine flooding and fuel pre-ignition can also occur.

How Many Injectors are in a 5.9L Cummins?

In general, a total of 6 injectors are implemented in a 5.9 Cummins. All these 6 injectors are noted to be high-pressure solenoid actuated fuel injectors.

In a 5.9 Cummins, these injectors are found to be mounted vertically into a bored hole present in the cylinder head’s top.

In each of these 6 injectors, fuel gets pressurized through the internal radial piston.

Due to this, the process of opening and closing the chamber outlet by a high-pressure solenoid valve takes place.

This chamber outlet is known to distribute unique fuel quantities to all the 6 injectors individually.

Common 5.9L Cummins Bad Injector Symptoms & Solutions

Once you notice your 5.9 Cummins is not running smoothly any longer or has started to blow black smoke, it becomes crucial to know what is going on.

This should be diagnosed as soon as possible, as avoiding the issue for a longer period will only make it severe.

Also, this could further result in out-of-pocket repair costs, or the engine might fail. Therefore, knowing the symptoms of a bad injector is of utmost importance.

This section has compiled a list of what to look for to detect bad injector symptoms 5.9L cummins. These are:

01. Extended Crank Time

Your dodge 5.9 Cummins taking a longer crank time than usual is one of the most typical symptoms indicating bad injectors.


This happens when the injector gets internally worn out with time. In other words, the return check value of the injectors will stop sealing any further.

Also, they will start to return massive amounts of fuel.

When this takes place, the 5.9 Cummins starts to struggle to build any more fuel pressure or might even completely fail in building pressure due to injectors being worn out.

Hence, extended crank time is caused since fuel in the injectors needs to get pressurized up to 4000 PSI.

This is important for the engine to start. But with a bad injector, the process will involve a lot of cranking time to reach that pressure.

In case only one injector has gone bad, then it would be able to build needed pressure after some time of cranking. However, if a few more have failed, then 5.9 Cummins would not start at all.


In any of the cases mentioned above regarding injector failure, replacing, or rebuilding all injectors is a good idea.

This is because one failed injector is likely to fail others as well. By changing all the injectors in one go, you can save your money and time.

02. Emission of excessive white or black smoke

One of the typical symptoms of bad diesel injectors in 5.9 Cummins is the excessive emission of white or black smoke.

Though, commonly, 5.9 Cummins releases black smoke occasionally, an increase in the amount than usual indicates issues with injectors.

If the exhaust is specifically sooty, then also a definite sign of your 5.9 Cummins injectors having problems.


A common reason for black smoke is incomplete combustion because of excessive fuel getting injected inside of the cylinders.

A worn-out injector starts to show slightly delayed injection timings or causes drip fuel.

That additional fuel collected further enters the combustion chamber and does not get completely burned, causing the black smoke to release.


If you notice excessive blow-up of black smoke, specifically under load, then it would be best to get the injectors checked.

Performing a cylinder balance test is the most effective way to determine which injector is having issues quickly.

03. Rough Idle or Slight Miss

If 5.9 Cummins is not smoothly idling or has been showing a slight misfire, then it is a good symptom that there is a problem with the injector’s plunger armature well or the nozzle pintle.


Possible rough idle in the 5.9 Cummins can be due to several things. Among them, the top cause is an internally leaking injector.

This type of internal leak happens because of worn debris or seat and nozzle pintle between them.

This specifically causes the additional fuel to enter the cylinder because of which the cylinder blows off the air-to-fuel ratio. This, in turn, causes a rough idle or misfire.


when you notice a rough idle, it would be great to examine all the injectors thoroughly to detect any internal leaking.

One way to do this is by performing a cylinder balance test or running an injector leak down test to find out which injector is prone to the issue.

A leaking injector can cause serious problems such as cracking or melting down pistons from excessive heat.

04. Dodge 5.9 Cummins not starting

Vehicle not starting at all is a symptom that either one or more injectors are having issues.

These issues could be injectors being stuck open and causing fuel to leak into the combustion chamber. Also, it could be due to injectors returning excessive fuel.


In the scenario where injectors are stuck open, it causes fuel to trip constantly into the cylinder resulting in a hydro lock.

This is when an excessive amount of fuel enters the combustion chamber, and the piston rod tends to band when it tries to compress it.


When you try to start a 5.9 Cummins, and it does not turn over, then do not crank your engine over for longer. This is specifically important when the injector is stuck open to avoid further damage.

05. Clattering, noisy, and loud Engine

All diesel engines are found to be noisy and loud inherently compared to gasoline engines. Birthday but the issue arises when one or more injectors begin to wear out on common rail systems.

This can be detected by symptoms like a sudden increase in noise a diesel-specific engine is making.

There would be louder sounds, increased ticking noises, and more clattering, especially when the engine is being lugged.


A worn control plunger or armature valve is often the cause for this. They tend to cause slight delays in their movements, affecting the timing of injection.


This issue can be reduced by using good-quality synthetic diesel engine oil or oil-based additives for injectors.

Another most effective solution for reducing diesel engine noise in 5.9 Cummins is using a quality damping material in every perceivable area.

These materials might be quite expensive, but they do absorb the sound efficiently.

Learn more about the 5.9 Cummins bad injector symptoms here from helpful tutorials

When Should Injectors be Replaced on 5.9 Cummins?

Fuel injectors for 5.9 Cummins can be replaced anywhere between 2,00,000 and 3,00,000 km if they are being treated properly.

This also indicates that injectors are running using clean diesel fuel of superior quality.

All diesel engines, including 5.9 Cummins, can provide a trouble-free and long-lasting working life when they are maintained as per the recommendations of the manufacturer.

This would include timely changing the filters, coolant, and oil and using only high-quality diesel fuel and engine oil.

 5.9 Cummins Injectors Replacement Cost

When you find bad injector symptoms 2004 5.9 cummins, the process of injector replacement on your 5.9 Cummins is not going to be a quick task.

This takes at least 6 to 8 hours to complete. If you are changing the injectors on your own, then an expense of 1,800 USD to 2,500 USD can be expected if a remanufactured injector set is being used.

This price can rise from 2,500 USD to 3,000 USD if brand new injectors are being used.

If the replacement is to happen at a mechanic shop, then an approximate payment of 2,500 USD to 4,000 USD can be expected.

These prices mentioned above are a rough estimation of the rates; the actual amount will vary according to the shop and state you live in.

Other factors that affect the cost of injector replacement are as follows: 

  • Small vehicles having fewer numbers of cylinders need less costly parts. Thus, its injectors replacement cost would be lower. On the other hand, bigger and high-performing diesel engine vehicles command a raised price tag.


  • Other issues regarding fuel systems, including defeated fuel pumps, etc., would need a higher replacement payment. This cost would depend on the specific issues and level of damage.

Top Questions

What to expect when one or more fuel injectors go bad on 5.9 Cummins?

The engine will misfire due to the bad fuel injectors. This issue causes the vehicle owners to experience sudden vibrations across the vehicle, and the motor will feel as if it is sputtering.

This kind of misfire happens when a bad injector affects the delicate balance between air and fuel entering the engine.

Can a defeated injector throw a code on the Dodge 5.9 Cummins?

Yes, it is possible that a defective injector can throw the code on the Dodge 5.9 Cummins. This will take place only for the circuit’s electrical side.

This electrical side gets consistently examined by the ECU for shorts, opens, and incorrect voltage. So, if the injector on the electrical side gets bad, it would show a DTC.

Which year 5.9 Cummins model is best?

The 5.9 Cummins between 1994 to 1998 are considered the best ones. These include Dodge 2500 & Dodge 3500.

When the performance potential is considered, the 12-valve 5.9 Cummins with mechanical P7100 equipped versions to cite as the best options.

They are rock-solid, simple designed, and highly reliable. They can easily cover miles up to half a million if maintained properly.

Final Thoughts

Hopefully, you find information provide in this article on 5.9L Cummins bad injector issues helpful. Diesel injectors on the 5.9 Cummins are specific about their needs.

Owners need to use high-quality and clean diesel fuel along with proper lubrication to make them run well.

Not following these practices can significantly decrease the injectors’ lifespan and functionality. You might end up paying thousands of dollars in constant repairs.