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Why are diesel injectors so expensive to replace?

You might not believe it but, diesels are easily one of the coolest engines to have ever been invented. High torque, high efficiency and low service requirements are all major benefits. But why are modern diesels so expensive to fix? More specifically, how can injectors on a newer diesel cost up to and over $1,000 each when compared to older diesels at $150 each?

Realistically, the tipping point in diesel injectors becoming so expensive was electronic control.

In the old days of diesel, fuel injectors had a direct line to a high-pressure pump that was timed to the engine. As the engine went through each cycle of cylinders, a lifter would force the injector open and cause a stream of ultra-high pressure fuel through the injector and into the engine.

These systems were incredibly simple and reliable over decades of use and millions of kilometres however, they also have a large number of drawbacks.

For example, throttle control was basically like turning a tap on or off, regardless of the RPM of the motor. This meant that at very low RPMs a large quantity of fuel could be injected which helped cause the giant plumes of black smoke we associate with old diesels now.

An additional problem with these older style injectors was that all of the fuel was injected in a single stage, which could lead to the characteristic knocking sound we all associate with diesels.

These injectors were incredibly simple and prices reflected this. However, as the industry progressed, so did injection technologies with the introduction of the common rail injector.

Unlike the diesel fuel injectors of old, these common rail diesel injectors have a high-pressure feed between all the injectors and use a computer controlled solenoid to pulse the opening of the injector.

This allows for a lot greater variation in the quantity of fuel available depending on the amount of throttle, boost and RPMs of the engine while also permitting things like multi-stage injection which opens and closes the injector multiple times per cycle to allow a more gradual and controlled burn of the fuel.

Even these couple of little things made a huge difference in both the efficiency and quietness of diesel motors though, they aren't without their own problems.

The problem with diesel fuel injectors comes down to the use case. As a diesel relies on the fuel being injected directly into the cylinder when the combustion charge is under the most pressure to work, the injection pressure has to be multiple thousands of psi at any one time.

While a normal, port injected petrol injection system might operate at 45-60psi, it's not uncommon to see common rail diesels operating at 30,000-60,000psi. This means the solenoid used to control the injection process has to withstand extremely high pressure while still being able to open and close some 15,000-30,000 times per minute, a truly incredible task that requires a truly specialised (and expensive) solenoid control.

What does this mean in layman's terms though?

Well, modern injectors have simply become more expensive due to the vast amount of features they have.

If the features are worth the additional cost is more of a thing for you to decide but, they have made modern diesels more powerful, more controllable and quieter which has helped to keep these workhorse motors on the road even facing tougher emissions regulations.


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