Symptoms of a Bad Diesel Injector

Diesel injectors are crucial for the vehicle’s engine, as a good injector supplies sufficient fuel for outstanding performance. Nevertheless, they may go “bad” due to some reasons, but you need to fix such issues soon. It would help if you don’t overlook any of the symptoms of a bad diesel fuel injector.

The diesel fuel injector provides the right amount of fuel needed and does so at the right time. With that, the combustion system can get sufficient diesel that takes care of the entire process. Often, these injectors consist of a nozzle and the injector body.

Interestingly, these injectors may get cracked, become tired, and starts wearing out. What are the typical symptoms of a bad injector pump? Well, I would be revealing some signs of a lousy diesel injector in this piece.

Knowing these symptoms would help you understand the right time to replace your car’s diesel injectors. Such action would prevent some engine problems and ensure you enjoy a smooth ride all through. 

Symptoms of a Bad Diesel Injector

It is pretty standard for diesel fuel injectors to have a short lifespan compared to their predecessors. However, the life expectancy of a diesel injector seems fair, reaching around 150,000 kilometers. 

Thus, they start wearing out with continuous use, and a damaged injector would reduce the car’s performance. Nevertheless, here are some signs you would notice when running a diesel with a bad injector.

how to test diesel fuel injectors

Engine Misfiring

At each ignition, an engine misfire would relay a strong message that the combustion system lacks something. What could that be? Well, in this case, it could be that there is no sufficient supply of diesel.

When the injector is bad, it does not pumps sufficient diesel needed for the proper ignition. If one of the cylinder’s diesel fuel charge fails to ignite, there is visibly a low amount of diesel pumped by the injector.

Uneven Idling

Ever noticed that your vehicle’s engine cranks but does not start immediately? It could be due to some damages to the diesel injectors. This sign seems like the commonest of them all, as you may begin noticing the engine idling.

In essence, if you start feeling your vehicle revving at varying speeds, it would help if you check the diesel injectors.

Bad Emissions

One common thing that car owners notice when the diesel injector appears clogged is the dirty emission from the exhaust pipe. Such emissions occur due to incomplete combustion within the combustion chamber.

You may start noticing white smoke from the exhaust pipe in some cases, causing severe environmental pollution. In essence, you should look at the diesel injectors of your car if the exhaust starts releasing some dirty emissions.

Diesel Fuel Smell

One may start wondering why the vehicle suddenly starts smelling like diesel. Well, that can also happen if the diesel injector is in terrible shape. It signifies a leakage, as this appears to be one of the typical “diesel injector seal leaking symptoms.”

Again, the car needs the right amount of diesel for proper functioning, and the injector needs to supply the fuel at the right time. So, if the injector develops a fault, it may let diesel flow out when it is not required or deliver in excess. Thus, you start perceiving that diesel smell.

Fuel Consumption Increases

A bad diesel injector would cause the car to consume more fuel than expected. Again, this issue has some severe effects on the vehicle’s performance. So, the efficiency of the car reduces, and further delay can lead to some more damages.

Engine Check Light

The engine check lights go on whenever there are some issues with the car’s engine. In most cases, the lights come on following issues like engine misfiring. Nevertheless, it would help if you scan the ECU code before further diagnosis. 

Such action would help determine the exact reason behind the check light turning on. If you notice codes related to an engine misfire, you may first check on the glow plugs. Try to see if they are in good shape before checking the diesel injector.

Engine Sputter During Acceleration

When the diesel injector is faulty, you may notice while accelerating. Such sputtering occurs due to the inability of the diesel pump to withstand the pressure from the tank’s supply. Thus, you should take the car to an expert to check the injector and work on it.

The common issues with diesel injectors are those with a leak or clogged or dirty injectors. With these signs mentioned above, you would tell when you need to change the fuel injector. 

Kindly note that clean injectors for diesel engines are a must. It is also advisable for car owners not to wait till they start seeing these signs before replacing their old injectors. A drive across over 100,000 miles would need that the diesel injectors get changed for the vehicle’s proper functioning.

Aside from these, some common causes of a lousy diesel injector include:

  • Dirty diesel supply: There may be some dirt, grime, or even grease mixed with the diesel. These contaminants may cause the injector to clog with time.
  • Defective O-rings: If the injector O-rings gets damaged, the diesel transfer timing may get disrupted.
  • Low diesel level in the tank: When the diesel tank seems empty, the injectors may start receiving air instead of diesel, and the bearing may not receive sufficient lubrication.

Thus, it would help if you tried to avoid these issues and maintain a good maintenance routine. Doing so would make the injectors last longer and performs optimally.


Q: How do you check diesel injectors?

When you start noticing some signs of a lousy diesel injector, it would be best to learn how to test diesel fuel injectors. You can check the injector by turning on the car and listening to the engine’s sound. A good injector would give off a clicking noise, which occurs with a good opening and closing of the valve.

You can also inspect the injector for any leaks and look at the emission from the exhaust pipe to know if the injector is in good condition. Furthermore, it would help if you tried to check the exhaust manifold’s temperature using an infrared sensor. Those manifolds that appear cold have faulty injectors.

Q: Can you drive diesel with a bad injector?

You can start the vehicle and maybe drive with a bad fuel injector, but it doesn’t seem safe. It is not advisable to drive with a faulty diesel injector, as it could cause severe issues for the engine. Thus, there is a need to fix such a problem when the need arises quickly.

Whether the diesel injector leaking into the cylinder or something else, it would help if you contact a car’s expert as soon as possible. Again, remember to replace the old diesel injectors after every 100,000 miles, even without any symptoms.

Q: How do you diagnose a lousy diesel injector pump?

Various signs can help diagnose a faulty diesel injector. One of such symptoms is issues running the vehicle. Since the engine does not receive sufficient diesel, the car may not accelerate properly.

You may also notice low pressure, engine misfiring, and excessive diesel consumption when the injectors are bad. Again, if you start hearing a high-pitch noise when starting the engine, it tells you that the injectors are faulty.

Q: How do you know when to replace diesel injectors?

In most cases, a bad fuel injector comes with an engine misfiring, and when you notice such, there would be a need to get them replaced. Nevertheless, it would help if you looked out for any fluctuating power, where the engine revs inconsistently.

Any possible smell of diesel in the car can also mean that the injectors are bad and need replacements. A sudden increase in the consumption of fuel can also mean that the old injectors need a change.

Q: Can you clean diesel injectors?

It is ideal for conducting a thorough cleaning for the diesel injectors after traveling across 30,000 miles. Kindly get your diesel injector cleaning kit to clear out the dirt and grime that clogs the injector. Such action would help the diesel flow properly.

Various cleaners work well in eliminating the contaminants in the fuel injector. However, it would help if you endeavored to turn off the engine before working on the diesel injector. Then, continue the process by disconnecting the diesel fuel pump.

Q: Should you use diesel injector cleaner?

It is suitable to clean the diesel injector using the right cleaner. These cleaning products come formulated for cleaning and unclogging the injectors. Such cleaners can also come in handy in getting rid of the sediments in the diesel tanks.

You can find different cleaners that work well for this purpose in various auto stores. With the help of such solutions, you can get out those deposits in the injectors that stop the proper transfer of fuel. In the end, the engine would have increased performance and works efficiently.

Final Words

A smooth ride can only be possible if the car’s components are in good shape. When a crucial part of the vehicle, like the diesel injector, goes faulty, it becomes difficult to keep the car running. Further delay of such issue may even cause some severe damages on the engine and cause you to spend more.

Thus, it would help if you don’t overlook the common signs you see. There are various symptoms of a bad diesel injector, and knowing them would help you fix the problem on time. Again, diesel injector testing can also aid further diagnosis and make the fixing process easier.


Hi there, I am R. Hasan Tito, a mechanic, and owner of this website. My friend and I created this website to share our knowledge, expertise, and experience with our fellow mechanics' community and car users. I am a specialist and certified automotive mechanic (Both Heavy Commercial and Private Cars). I worked as a Mechanic and Mechanic Supervisor for over fifteen years at Global Rebound Automotive companies - Toyota, TATA, BMW, Nissan, TVs, and Others. Now, I enjoy my new role of leading a team of automotive experts (in their respective fields) and publish new content on a regular basis on my website and social media.

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