Can You Replace One Fuel Injector or the Full Set? Read This!

When dealing with a faulty or an old diesel fuel injector that needs replacement, a common question that comes up is whether one should replace the one faulty injector in your engine, or the entire set of diesel fuel injectors?

If you run Bobcat machines with the Doosan engines (D18, D24, D34) in excavators, skid steers, track loaders, Toolcat machines, loaders, or tow compressors, this decision can directly affect your downtime, repair costs, and long-term engine health.

We’ve talked a lot about the role of diesel fuel injectors in your engine, along with signs to look for if you suspect that you’re having problems with your injectors.

In this guide, we’ll walk through the key factors that help you decide whether to replace a single injector or all of them, and why the “right” answer can change depending on mileage, cause of failure, budget, and how critical your machine is to daily work.

Important Note Before You Start: Label Your Injectors

If you are personally planning on inspecting your injectors, only remove the injector you suspect is faulty (if possible). If you must remove all injectors, label each one in order as you remove them.

Each injector needs to be matched and coded to the ECU. Mixing them up can cause more problems than you started with, especially on engines like the Doosan D18, D24, and D34 commonly found in Bobcat machines.

Tip #1: Check the Condition of Each Injector. Are the Others at the End of Their Life?

Let’s say your check engine light turns on and diagnostics point to one faulty injector. Before you decide to swap just one, ask yourself:

• Have you conducted a leak test?
• Have you the other injectors ever been cleaned?
• Do you notice early signs like rough idle, white/black smoke, misfires, or poor fuel economy?
• Do these injectors have 50,000+ miles on them already? 

If you answered yes, to any of these questions, there’s a good chance the rest of the injectors are not far behind in terms of wear. The reason why is that there may be a short while left before another one of your injectors gives out and starts having issues. Replacing one or four injectors is a process that costs you time and money, so its usually better to change all injectors at once while your machine is down. 

Furthermore, cleaning injectors is highly recommended as part of routine maintenance, but it cannot reverse internal mechanical wear. Once an injector is worn, cleaning alone won’t restore it to “like new” condition.

If you are not inspecting the injectors yourself, considering removing all four and bringing them to a mechanic to check. 

On the other hand, if your injectors are relatively new and you’ve confirmed the failure is due to a rare defect rather than age or fuel contamination, replacing just the one faulty injector may be enough.

Tip #2: What Caused The Problem? 

Before you click “add to cart” on that new injector, step back and ask:

“What actually caused this injector to fail?” 

Some common causes include: 

• Old age and natural wear
• Contaminated fuel (water, dirt, metal particles) 
• Excessive heat
• Electrical issues in the wiring harness
• Problems with the fuel pressure controller or driver subsystem 
  

If the failure is caused by: 

• General wear and tear: That points to age, other injectors may be close behind. Consider a full set replacement. 
• Fuel system contamination: Replacing just one injector without addressing the root fuel problem can be a short-term band-aid. You may need to inspect or replace:
  • Fuel filters
  • High pressure fuel pump
  • Fuel common rail
  • Fuel lines
  • Fuel tank (if contamination is severe) 
• Electrical or ECU issues: In this case, replacing injectors alone may not fully resolve the issue. You might need a wiring and ECU diagnosis to prevent repeated failures.

Understanding why the injector failed can save you from buying more injectors than necessary, or from burning through multiple sets because the real problem is elsewhere.

Tip #3: How Fast Do You Need the Machine Back? Downtime Changes the Decision

We know that many machine operators only have one or two machines that they rely on and use everyday. For many, a down machine means a loss in money, so if you need your machine repaired as soon as possible, then we recommend purchasing an entire new set. Sending them off to a dealer to get your fuel injectors checked has many benefits, but not on saving time. If speed is your top priority, especially during busy season, the safest bet may be to replace the full set immediately so you don’t risk another injector failing in a few weeks or months.

Tip #4: Who Is Doing the Replacement? You or a Mechanic?

This is another important factor to consider. If you are comfortable working on engines, you understand torque specs, cleanliness requirements and can code the injectors to the ECU, then replacing just one faulty injector can be a reasonable choice. 

On the other hand, if a mechanic is doing the job, that means you're paying someone hourly labor rate, potential shop fees and scheduling/transport time. In that case, having a mechanic replace all four injectors in one visit can save you money and hassle long term so you can avoid the risk of paying for labor twice and having additional downtime for your Bobcat machine. Think of it like replacing brakes: if all components are worn, it usually makes more sense to service everything at once instead of fixing one tiny section and coming back again a month later.

Tip #5: Buying Four Injectors is Sometimes Cheaper Than Buying One — Bulk Order

In some cases, buying the entire set of diesel fuel injectors for an engine like the D24 or D34 means you can actually pay less when you divide the cost of each injector. We personally discount our set of fuel injectors vs when someone purchases a single injector from us. Buying in bulk is usually more economical. 

To rebuild or purchase new? We recommend purchasing new fuel injectors. 

You can either purchase a new injector or send them out to be rebuilt. Oftentimes, sending your used injectors to be rebuilt can take a long time and end up costing you more in the long run. We also don’t recommend rebuilding them at home due to the complexity of this process. Facilities that specialize in rebuilding fuel injectors work and operate out of clean environments in order to prevent particles such as dirt or dust from contaminating these parts.  

Do you have any other tips worth keeping in mind when considering, “do I have to replace all injectors or just one?” If so, email us at contact@expertdieselparts.com. We’d love to add them to this list. 

We hope this was helpful. Don’t hesitate to reach out with questions on your parts or if you’re searching for a part. 

Are you looking for high quality diesel engine parts such as fuel injectors, fuel pumps, crankshafts, turbos and more? Specifically looking for new diesel fuel injectors? Check out our wide selection of fuel injectors for your machines.

The information provided in this article is for general guidance only. Always refer to your machine’s manual or consult a qualified mechanic before performing any maintenance or repairs.