Bad Fuel Injector Symptoms, Problems & Solutions (Clogged)

Bad Fuel Injector Symptoms: If you are like us, any kind of engine sputtering, power loss, ignition delays, and other “fun” problems make your blood boil. One of the common causes for the issues we described above is bad fuel injectors. The fuel injectors or nozzles as they are called in diesel engines have become incredibly precise and technologically advanced. While this has its benefits, it also brings about a load of trouble. This article is your ultimate guide to bad fuel injector symptoms, causes for those symptoms, and the solutions for those problems. We also did our best to include DIY fuel injector cleaning tips that actually work.

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What do fuel injectors do?

Fuel injectors essentially deliver the appropriate amount of fuel to the engine before each combustion cycle. Each of the engine cylinders receives the same amount of fuel that is properly dispensed as a mist for an optimal burn in the combustion chamber. Any deviation from the perfect delivery of fuel to the cylinder can result in serious engine problems or even a complete breakdown. An electronic unit calculates and controls the electrical impulses for opening and closing the injectors based on the current demand of the driver. The control unit opens the injector for a time that is needed to inject the right amount of fuel. Fuel injectors are made up of a valve body. The valve body contains a magnet winding with a guide for the nozzle needle and a nozzle needle with a magnet.

Do all cars have the same fuel injector systems?

Of course not. Engines can either have direct fuel injection or indirect fuel injection. Fuel injectors on modern common rail diesel engines and modern direct-injection petrol engines operate under a much bigger pressure as they dispense a dose of fuel directly into the combustion chamber. This allows for much better engine performance and better fuel efficiency. However, such fuel injectors are much more precise and prone to failure. 

On the other hand, indirect fuel injection engines deliver the dose of fuel to a precombustion chamber. The fast-moving air in the indirect fuel injection then mixes the fuel with air and prepares it for combustion. Such engines are much more reliable, less complicated, and less expensive to manufacture. This system also allows for smaller diesel engines to be produced that are more likely to accept alternative fuels that are not as refined.

Symptoms of bad, clogged, dirty or faulty fuel injectors

Symptoms of bad fuel injectors directly impact the engine. If you have a faulty fuel injector you will surely notice. The problem is, that the symptoms of bad fuel injectors are easily misdiagnosed with other engine problems. Symptoms of bad fuel injectors include:

  • Engine starting problems
  • Power loss problems while driving
  • Increased fuel consumption (decreased fuel efficiency)
  • Fluctuating engine RPMs when idling
  • Increased engine emissions
  • Check engine light flashes on the dashboard
  • The engine misfires
  • A smell of fuel fumes around the car and inside the cabin
  • Fuel leaks that can lodge the injector into the engine and mix with engine oil
  • A non-metallic knocking sound that gets louder as you accelerate. Faulty fuel injectors can be at fault for this specific sound.

Ignoring bad fuel injector symptoms eventually leads to:

  • Early engine failure by not only destroying the cylinder head but the entire cylinder due to an uneven fuel spray pattern
  • Damaged catalytic converter and DPF (Diesel Particle Filter)

Common fuel injector problems and causes for defective fuel injectors

Most of the symptoms listed above come as a consequence of clogging, injectors coking, short circling in the solenoids of the injectors, deposits from fuel additives and broken connections to the control unit. 

  • Clogged fuel injectors are a common malfunction. Clogging occurs because the ultra-fine bores of the injection valve are extremely sensitive to the smallest impurities in the fuel or fuel additives The clogging can cause permanent failures of the fuel injectors. Clogged fuel injectors do not disperse the fuel mist properly in the combustion chamber. A clogged fuel injector can shoot a jet of fuel directly onto the cylinder head which causes serious damage if you ignore the issue.
  • Dirty fuel injectors are a consequence of hydrocarbons and other additives that are present in the fuel. These can combine with carbon which leaves residues that we call “dirty fuel injectors”. Dirty fuel injectors can be cleaned with certain additives.
  • The fuel injector does not open. This means that the fuel injector will not deliver the fuel needed in the cylinder. A new fuel injector is the only solution.
  • The fuel injector gets stuck on open. You can imagine that constantly leaky fuel injectors cause havoc in the engine. This is rare but it does happen. 
  • Due to the high-pressure environment that direct injection fuel injectors work in, the edges of the valves (part of the fuel injector) suffer damage that leads to an incorrect spray pattern.
  • Another common, but deadly fuel injector problem is the coking of the injection valves. Coking is essentially a gathering of solid carbon deposits on the internal surfaces of the injector. This is caused by the evaporation of unburned fuel when the engine is turned off at high temperatures. A certain amount of coking is therefore always present. If the engine is generally in a good state, coking should not be an issue for a long time.

Bad Fuel Injector Symptoms: How to clean fuel injectors at home?

Cleaning bad fuel injectors with fuel additives

In older vehicles, using a fuel additive to clean bad fuel injectors almost always leads to an improvement in injection behavior, since the additives actually dissolve the deposits on the nozzles once the additive is added. However, do not expect a big increase in engine performance. But the emissions behavior is 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 misfiring disappeared. However, such cases are rare, especially in modern engines with precise fuel injectors. Such symptoms usually require professional cleaning (the removal of the injectors is needed) or even replacement of the injectors. If you decide to use a so-called fuel injection system cleaner on your engine, you should first contact the vehicle manufacturer to find out about the safety of specific cleaners. Because the additive is poured into the fuel tank and thus gets through the entire fuel system, including pumps, high-pressure pumps, pressure regulators, and nozzles.

Cleaning bad fuel injectors in an ultrasonic bath

Dirty fuel injectors that (in some cases) can be easily removed can be cleaned in an ultrasonic bath. It is also helpful to clean or, if possible and present, replace the microfilters located above the fuel injectors. Over time, the filters might become clogged with the finest particles, so that the original throughput can no longer be achieved. The cleaned fuel injectors are installed with new sealing rings.

how a fuel injector works
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Professional fuel injector cleaning and diagnosis

Some companies offer professional cleaning of petrol and diesel fuel injectors. Bad fuel injector symptoms are best resolved in a professional setting. The valve is also controlled here during cleaning, just like it is inside the engine. This means that the nozzles open and close, which optimizes the cleaning process. In addition, such specialist companies can also check the spray pattern of the fuel injectors on a test stand. Furthermore, the throughput and the flow rate can be checked. In order for the engine to run optimally, it is important that all of the engine’s injection nozzles have approximately the same throughput since the different injection quantities of the individual cylinders have to be compensated for by the engine control unit.

Keep in mind that not all fuel injectors can be cleaned and saved, some injectors are beyond repair. Another thing to remember is that professional cleaning can be quite expensive, especially with the cost of removing and installing the fuel injectors back in the engine. If you get new fuel injectors for a decent price, installing new fuel injectors can be just a bit more expensive but much more reliable in the long run.

A professional service center that specializes in fuel injectors will have diagnostic tools that can read the error “memory” of each fuel injector and the cable connections leading to the fuel injectors. In any case, a professional diagnosis is your best bet to resolve your fuel injector issues at the best price.

How to extend the lifetime of fuel injectors

Bad fuel injector symptoms are bound to happen at some point in a cars life cycle. There is no magical recipe to keep your fuel injectors lasting for a lifetime. The best and the most basic thing you can do is to regularly replace your fuel filter as is prescribed by the manufacturer of your car. Certain car manufacturers also sell their own fuel additives that are 100% good and healthy for all of the components in your car. BMW is one of those brands for instance. Cars with precise fuel injectors, which is basically all cars made in the last 15 years are also meant to be driven on the highest grade petrol or diesel. Do not fill up your car with low-grade fuel that contains detergents and additives which are responsible for fuel injector clogging.

Here is a good article explaining why fuel injectors need periodic cleaning.

If your mechanic suspects that you might have dirty fuel injectors, getting them cleaned with an ultrasonic bath is the best approach, it is cheap and incredibly effective. It is certainly a lot cheaper than spending 150$+ on a single new fuel injector.

How much do new fuel injectors cost?

Fuel injectors are not a simple component of your fuel system as they used to be. They are highly technologically advanced nozzles that are not cheap by any means. Most of the fuel injectors of modern cars are priced at 150$ or more, meaning that a 4 cylinder engine will have a total of 600$ worth of fuel injectors inside. The more cylinders you have, the higher the cost of a replacement. Do not forget to take into account the labor cost for replacing the injectors. It is definitely not a cheap service. You can also buy refurbished fuel injectors that do come cheaper but they are never as reliable as new ones.

What are piezoelectric electric fuel injectors and can they be cleaned?

Piezoelectric fuel injectors use an array of piezo crystals that expand under a surge of electric current and contract as they are discharged. By employing this technology, the fuel injector opens up when needed, delivers the fuel, and closes back up when the electric charge is taken away. Certain car manufacturers like BMW and Toyota use this principle of fuel injectors but it is not common.

For a long time, cleaning piezo fuel injectors was not possible, however, times changed. Yes, piezoelectric fuel injectors can be cleaned and it is certainly much cheaper than new and expensive piezo fuel injectors. The success rate of cleaning however is still a hot topic in the automotive community as many people claim that it is not as sufficient as it should be.

Bad Fuel Injector Symptoms: Conclusion

Fuel injectors are an essential part of your engine. Keeping them healthy should be one of your main priorities as a car owner. Failing to do so can lead to expensive engine damage which is something you do not want to be dealing with, trust us. Do you have any questions, or do you wish to share your experience with bad fuel injectors? Tell us and share your story in the comments below.

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