This is how the injector cleaner works

Injectors (fuel injectors): defects, symptoms, and cleaning

Injectors, also known as fuel injectors, give the engine the right dose of fuel before each combustion cycle. Injection nozzles in diesel engines are usually referred to as injectors. Whether gasoline or diesel, injection nozzles are prone to defects in both types of engine.

➤ Benefits of fuel injection
➤ Manifold injection and direct injection
➤ Reasons for defects in injection nozzles
➤ Symptoms of defective injection nozzles
➤ Clean the injection nozzles with the injection system cleaner
➤ Clean the injection nozzles in an ultrasonic bath
➤ Professional cleaning of injection nozzles
➤ Cleaning the injection nozzles: costs
➤ Check injection nozzles in the workshop
➤ Cost of injection nozzles

Advantages of fuel injection

In the past, injection nozzles still worked mechanically, today they are electronically controlled solenoid valves that have become true precision instruments. The nozzles are networked with other components and sensors relevant to combustion via the engine control unit. At the end of the 1980s, gasoline injection largely replaced the carburettor because it offers many advantages. The most important thing is to reduce fuel consumption, because compared to modern injection systems, carburettors are more or less better watering cans. In addition, gasoline injection enables the use of a regulated catalytic converter and is therefore jointly responsible for significantly cleaner exhaust gases.

Manifold injection, direct injection, or both

Intake manifold injection: In contrast to direct injection, the fuel is injected in the intake manifold and has to pass through the intake valve.

© Bosch

One engine has one injection valve per cylinder. The injection nozzles atomize a very fine fuel mist either in the intake tract (intake manifold injection) or directly in the combustion chamber of the cylinder (direct injection). Some modern engines also offer a combination of direct and manifold injection, such as the Audi R8 V10.Depending on the load range, intake manifold and direct injection alternate with the aim of reducing the formation of nitrogen oxides. This precisely metered atomization of injection nozzles ensures more optimal combustion of the fuel, which results in better power delivery. But in order to achieve such a fine atomization, the fuel must be injected with overpressure. With manifold injection, where the injection nozzles are supplied with fuel via a common injection rail, the injection pressure is around three to six bar. With direct injection, where the injection nozzles are fed by a high-pressure pump, it is up to 350 bar. By far the highest injection pressures are achieved with compression-ignition engines: modern common rail diesel engines, which also work with direct injection, reach up to 2500 bar.

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Reasons for injector failure

Injection valves for manifold injection: the tiny openings are barely visible. Deposits can rarely be seen with the naked eye.

© Bosch

As a rule, the more precise the technology, the more vulnerable it is. Since the ultra-fine bores of the injection valves can quickly become clogged, for example by poorly filtered fuel, this can lead to blockages and permanent failures. This does not necessarily have to be noticeable through combustion misfires, but the problem should be resolved. This is because even a slight change in the atomization of the fuel can have a detrimental effect on the consumption and the performance of the engine. The injection nozzles of direct injectors are exposed to particularly high levels of stress in the combustion chamber. There is even a risk that other components will be affected by a changed injection behavior. Defective injectors can burn holes in the piston, because instead of a fine mist, a jet of fuel is generated that burns directly on the piston crown. Due to their location in the combustion chamber, direct injection nozzles are exposed to particularly high levels of stress. In some cases, the material cannot permanently withstand pressure and heat, and the valves fray at their edges, which also leads to a deteriorated spray pattern. Much more often, however, with direct injectors, the injectors coke, which means that some of them fail completely. Other defects include short circuits in the injector solenoid coils, deposits from additives and brittle cable connections to the control unit.In addition, worn sealing rings on the injection valves can lead to leaks and thus to loss of fuel.

Symptoms and consequential damage from defective injectors

Injection valve of a direct injection engine: Since the valves mostly run vertically through the cylinder head, they are much longer.

© Bosch

Depending on the degree of damage, a disturbed fuel supply due to one or more defective injection nozzles can be felt differently. From imperceptible drops in performance, deteriorated exhaust gas behavior and starting difficulties to increased consumption, restless idling, flashing or permanent lighting of the engine control lamp, to engine knocking (uncontrolled ignition of the gasoline) and permanent combustion misfires, everything is possible. The consequences of defective injection nozzles can be serious.If unburned fuel gets into the particle filter or catalytic converter, it can be destroyed. If the misdirected fuel jet washes off the oil film on the cylinder wall in direct injectors due to a defective injection nozzle, this can even result in a seizure of the piston. So if you notice the symptoms described in your car, you should go to a workshop as soon as possible.

Clean injection nozzles with injection system cleaner

In older vehicles, cleaning the injection nozzles almost always leads to an improvement in the injection behavior, since the additives and the deposits on the nozzles are actually dissolved by adding the additive. The resulting increase in performance is usually barely noticeable. But the exhaust gas behavior is also improved thanks to the more optimal combustion in the engine. In rare cases, users of such additives reported that even stubborn deposits could be dissolved and serious problems such as combustion misfires disappeared. However, such cases are rare; such symptoms usually require professional cleaning (including removing the injectors) or even replacing the injectors. Anyone who decides to use a so-called injection system cleaner on their engine should find out about the approval of specific cleaners from the vehicle manufacturer in advance. Because the additive is tipped into the fuel tank and gets through the entire fuel system, including pumps, high-pressure pumps, pressure regulators and nozzles.
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Clean injection nozzles in an ultrasonic bath

Before and after cleaning: The cleaned injection nozzles are given new seals and a new microfilter before they are installed.

© BAR-TEK Motorsport GmbH

Stubbornly dirty injection nozzles that can be easily removed (intake manifold injection) can be cleaned in an ultrasonic bath. It is also helpful to clean or, if possible, replace the microfilters above many of the nozzles. Over time, they have become clogged with the finest particles, so that the original throughput is no longer achieved. The cleaned nozzles are installed with new sealing rings.

Professional cleaning of injection nozzles

The spray pattern of the injection nozzles can be checked on the test bench.

© BAR-TEK Motorsport GmbH

Some companies offer professional cleaning of injection nozzles and diesel injectors. The valve is also activated here during cleaning. This means that the nozzles open and close, which optimizes the cleaning process. In addition, such specialist companies can also check the jet pattern of the nozzles on a test bench. Furthermore, the throughput and the flow rate can be checked. For optimal engine operation, it is important that all of the engine's injection nozzles have approximately the same throughput, since the engine control unit has to compensate for the different injection quantities of the individual cylinders. It only works to a certain extent.

Cleaning the injectors: costs

The costs for the professional cleaning of injection nozzles mainly depend on the type of injection nozzle. The cheapest way to clean intake manifold injectors is: Cleaning a nozzle costs from around 30 euros. In the case of injection valves of direct injectors, between 40 and 70 euros per valve must be taken into account. Piezo injectors, often found in diesel, are cleaned for 70 to 90 euros each. In addition to the prices for cleaning, there are the costs for installing and removing the nozzles. Experience has shown that this is the greater cost factor for direct injection engines. Because the injection nozzles are often difficult to reach. In the case of diesel engines, special tools are required to remove the injectors that are usually very stuck. Depending on accessibility and the number of nozzles to be removed, up to five hours of wages can be incurred for removal and installation in the workshop. In some cases it is impossible to avoid the destruction of the stuck injection nozzles.

Injector type | Prices (approximate)
Manifold injectors | 30 euros
Direct injection nozzles | 40 euros
Piezo injectors | 70 euros

Check injection nozzles in the workshop

Workshops have several options to check the function of injection nozzles without having to remove them. This begins with reading out the fault memory and checking the cable connection of the injection nozzles using a multimeter. A fuel pressure test may reveal other defective components, such as a defective high pressure pump, a worn fuel pressure regulator. In addition, the resistance of the injector solenoid coils can be checked with the aid of an ohmmeter. An oscilloscope can display the voltage and the pulse duration of the individual nozzles in order to compare the values ​​with the nominal data.

Cost of new injectors

The cost of new injection nozzles is very different. Injection valves that work in the intake manifold are already available for less than 40 euros. Injection nozzles from modern direct injectors and injectors from common rail diesels, on the other hand, can cost over 200 euros. Annoying when there are several injection nozzles that have to be replaced. In addition, there are the costs for installation and removal. This is sometimes very time-consuming, especially with direct injection engines and modern diesels. The exchange of two injection nozzles, including removal and installation, easily adds up to over 1000 euros.