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How to Tell If Injection Pump Is Bad

Posted by Scott Goldfarb on

Injection pumps are prone to wear and tear over time due to their complexity and their constant use. Drivers who know how to tell if injection pump is bad can take measures to address potential issues and avoid expensive repairs later on.

Sometimes, the problems related to the injection pump aren’t immediately obvious and can gradually worsen, so it requires a keen eye, excellent hearing ability, and a solid understanding of common signs to detect the problem.

The article will equip you with the knowledge needed to identify problems related to the injection system, specifically with the pump.

How to Tell If Injection Pump Is Bad

Source: shutterstock.com/ Photo Contributor: Nordroden

How to Tell If Injection Pump Is Bad

Different methods exist on how to know if diesel injection pump is bad, especially if you’re quite familiar with your car. The symptoms are audible or visible and are also detectable while feeling the car’s capacity on the road.

A significant drop in the car's performance is the most glaring indicator of a pump malfunction. Frequently, it’s accompanied by other symptoms like hard starting, rough idling, and visibly increased exhaust gas emissions.

Sometimes, malfunctions get discovered during regular checkups as they are undetectable to the driver. That’s why it’s important to regularly inspect the pump’s performance, as it’s possible to discover problems before they escalate.

Here are the symptoms to look out for when you suspect there are issues with your engine’s injection pump:

  • Hard starting
  • Reduced engine power
  • Increased fuel consumption
  • Visible increase in exhaust smoke
  • Rough idling 
  • Delayed response during acceleration
  • Misfiring

Because the pump is responsible for the entire fuel delivery process in the engine, any malfunction can disturb the effectiveness of the combustion, which is crucial to generating power for the car.

Common Injection Pump Issues

The injection pump and its components are prone to wear and tear because of the massive amount of work they do. The large amounts of fuel that pass under high-pressure conditions can cause the pump to deteriorate over time.

The manufacturer usually determines the optimal frequency for performing checkups or replacing the pump. The time for inspection ranges from two to four times a year, depending on the severity of the driving conditions. 

Also, you should replace the pump every several years or after a specified mileage indicated by the manufacturer.

So, the most common issues of the injection pump include: 

1. Worn internal components

Wear and tear of injection pump components is one of the most common issues in the injection system. The injection pump uses precisely fitted parts like plungers and barrels that control the timing and amount of fuel that goes into the cylinders. 

The repetitive nature of their work in the engine and the environment consisting of high heat and pressure causes these components to deteriorate over time. 

As they wear down, they begin delivering inaccurate amounts of fuel with less accurate timing, which leads to several issues regarding the combustion.

2. Seal and gasket leaks

Seals and gaskets keep everything together, and when they start degrading, it can lead to leaks and air infiltration. As a result, it can disrupt the precision of fuel delivery and a significant drop in engine performance.

Signs of seal and gasket leaks include the smell of fuel and visible stains around the injection pump. In some cases, the stains are only detectable with a touch, so that’s one way to know how to tell if injection pump is bad. 

If there is wetness around the injection pump accompanied by irregularities in the engine’s work, the pump may suffer from leaks.

3. Insufficient lubrication

The smooth operation of the injection pump relies on adequate lubrication. It softens the friction between the moving parts and thus reduces the wear and tear. 

In diesel engines, the fuel acts as a lubricant and provides benefits to some components of the pump, but the fuel alone is not enough.

Additionally, if the fuel contains contaminants like dirt or water, they can interfere with its lubrication properties. This puts the injection pump in danger of having an increase in friction and potentially damaging the internal components. 

Regularly using filters for the fuel while using the best quality fuel can prevent some of these issues.

4. Clogged fuel filters

Clogged fuel filters are a common issue for diesel engines that impact the functionality of the injection pump. 

Fuel filters are crucial for removing contaminants like water, dirt, and debris before reaching the injection pump. Once the contaminants make it through, they can cause multiple issues.

With clogged filters, the pump won’t be able to receive the necessary amount of pressurized fuel. This will inevitably result in loss of engine power and bad acceleration.

Clogged fuel filters

Source: shutterstock.com/ Photo Contributor: HenadziPechan

5. Electrical problems

Like the previous issue, this is unrelated to the injection pump. Rather, it happens elsewhere and leads to improper pump functioning.

In modern engines, the electronic systems command the injection timing and quantity, relying on sensor inputs. Those sensors' defects will disrupt the injection pump’s operation and cause performance issues.

Diagnostic Tools and Techniques

The use of specialized diagnostic tools greatly improves the accuracy and efficiency of injection pump diagnostics. 

The various tools used for this purpose provide precise data and identify specific issues, which is valuable for making more informed decisions. This is valuable because various problems with the engine and the car can manifest themselves in a similar manner.

The sensory inspection is still the best way to determine the presence or the extent of issues with the injection pump. Abnormal noises, finding leaks by touching suspect areas, or seeing an excess of exhaust gases can provide valuable information.

For performing more advanced inspections, you need to have more advanced tools such as:

  • Scan tools
  • Fuel pressure gauge
  • Dial indicator

Scanning for errors in the codes stored in the ECU could reveal valuable information regarding the problem. 

Moreover, measuring the pressure of the fuel is important for knowing if the pump delivers the required amount of pressure to achieve atomization and combustion. 

The dial indicator is another tool that assists in measuring the movement of the inside components, providing information for irregularities and inconsistencies in the operation.

Common Mistakes

In the auto industry as a whole, there are many myths and misconceptions that pass as knowledge, even though they have little to do with reality. 

It’s important to note that the common symptoms associated with injection pump issues can also be indicators for other problems.

Without proper diagnosis, it’s not advisable to perform interventions as you can make the problem worse and cause additional damage. 

The following tips will help you read the clues better and avoid making some common mistakes when detecting issues in injection pump:

Excessive smoke

While it can point to issues with the injection pump, it can also mean that there could be air intake problems, faulty injectors, or improper timing. As one of the signs of a faulty injection pump, it is usually accompanied by a notable decrease in performance.

Fuel additives for repairing

Fuel additives like cetane boosters and injector cleaners are often believed to fix injection pump issues. The reality is that they are a good preventative measure but cannot fix pump issues.

Replacing the pump

Many people consider that fixing any injection pump issue requires replacing the injection pump altogether. 

While it’s true that a new pump will solve the issues, it’s an unnecessary expense if the problem can be fixed by only replacing the faulty components.

Rough idling

While it can sometimes be because of pump-related issues, it’s also possible that there are glow plug problems, clogged air filters, or issues with the exhaust. 

When experiencing rough idling, always look for accompanying symptoms like poor acceleration.

Rough idling

Source: shutterstock.com/ Photo Contributor: virgmos


The injection pump is a key component of diesel engines that’s responsible for delivering a precise amount of fuel for combustion. Recognizing issues with the pump on time is crucial for extending its lifespan and maintaining its high performance.

Due to the high-pressure environment, the pump is prone to issues like worn internal components and leaks. Symptoms like hard starting, reduced power, and rough idling are common indicators of something wrong with the injection system.

The most common mistake you can make is when diagnosing the issues, as one symptom can indicate several possible problems. So, how to tell if injection pump is bad? Using diagnostic tools is the best method as it prevents giving a wrong diagnosis.


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