Fuel Injectors

All you need to know

In this article, we will look at what a fuel injector is; we will also look at how an injector goes about doing what it was designed to do, the types of fuel injection in use, and lastly we will tell you more about how to be aware of the problems that fuel injectors may display. If you are uninformed about any or all of these aspects, then this article is for you. Information empowers a vehicle owner to identify vehicle related issues fast. This should then move owners to address such issues by having them fixed. Use your senses: look and listen, smell and feel – but what will you look at, or listen for, and what will a specific odour or touch mean if you do not possess the relevant knowledge to bring it together with these sensory observations?

At Steves Auto Clinic, leader in the field of automotive servicing and repairs, we aim at giving you the information required to do just that, to bring together that which you see, smell, hear and feel, to what you know. Read on, be empowered, who knows how the following information may one day be of service to you or someone you know!

What is a Fuel Injector?

We know that the major parts in a vehicle work together to make driving possible. It will not be fair to argue that the one is more important than the other is, yet we do that sometimes. People tend to say that their vehicles cannot run without fuel, but how will it run if you short a piston, or a spark plug is broken, or a wheel is missing? To say that the one is insignificant to the other is unfair. Let us look at another point! You have fuel, but how do you think that fuel reaches the point to enable combustion? Combustion can only happen when there is oxygen, fuel and a spark (in the case of petrol engines). The air intake system is designed to deliver oxygen to the cylinder and the fuel injector receives signals from the engine control unit (ECU) and see to it that fuel is injected in correct quantities into the intake manifold or combustion chamber. In a nutshell, the main purpose of the injector is to inject, but without jumping the fence, let us move on to the part where we will look deeper into the working of this little component.

How does it function?

That is a good question, and something that not only inquisitive-minded people should ask, but something that every vehicle owner should ask too. If you know how it functions, then you will know how to treat and troubleshoot it better.

We know that the primary purpose of the fuel injector is to inject the fuel – that could have been deduced from its name right from the beginning of this article, but the working is not that simple. Fuel injectors do not just inject willy-nilly, no, they have to deliver the exact amount of fuel required by the engine, requirements that change fast and frequently. This exact fuel-air mixture required will depend on the type of engine, the fuel used and the requirements of the engine (its power, fuel-economy, exhaust emission levels etc.).

We also know that the injector is a component with electronic controls that receive signals from the ECU to ensure exact fuel delivery. The Wikipedia injector animation may assist you in the further development of this discussion. This then, is what happens to ensure that a fuel injector function according to its design.

Fuel Injector

Pressurized fuel is delivered to the fuel injectors; the ECU tells the injectors when to open a valve to let the fuel pass through. The fuel pass through an atomizing nozzle (more about atomization later) and the injectors then spray a fine mist of fuel into the engine’s intake manifold or combustion chamber. The mist spray contributes to making the vehicle more fuel-efficient and environmentally friendly by polluting less. The injector is screwed, nozzle side first, into either the inlet manifold or the cylinder head, and at such an angle that the fuel is sprayed towards the inlet valve.

A few words about atomization: according to Khair & Jääskeläinen (2013), fuel atomization is the process that ensure that fuel atomizes into very small fuel particles. This is a primary design objective for diesel fuel injection systems. Small spray droplets ensure that all the fuel has a chance to vaporize and participate in the combustion process. This means better combustion.

There you have it, you now displaced yourself from the circle of people who knows nothing about fuel atomization (and the greater working of the injector), to the much tinier circle of those who do! Knowing what it does and how it works, still tells us nothing about the types of injectors, so let us have a peek at them.

Types of Fuel Injection

Who can remember the days of throttle body fuel injection? That was back in the day when fuel injection was still in its infancy, when it was retrofitted to engines that were designed to use carburettors. Someone once said that the only thing that stays the same is that nothing stays the same, so technology eventually moved forward to the point that different types of fuel injection is in use. Some systems are superior to others, and you may wonder what type of fuel injection your vehicle may use. Let us have a look at the main types of fuel injection.

According to Bruzek (2016), the fuel injection types used in newer vehicles include four basic types: Single-point or throttle body injection; Port or multipoint fuel injection; Sequential fuel injection, and Direct injection.

Single-Point or Throttle-Body Injection (TBI)

The TBI was the earliest and simplest type of fuel injection. It replaced the carburetor with one or two fuel-injector nozzles in the throat of the engine’s air intake manifold (the throttle body). Though not as precise as the systems that followed it, it still metered fuel with better control than a carburetor and is less expensive and easier to service. Due to its high flow rate, it also do not clog up that easy. If you have an issue with an injector, you only have to replace one. The TBI system is not as fuel efficient as modern systems. The system is also unpopular nowadays; people consider it inaccurate because when you lift your foot from the accelerator, there will still be fuel left in the air mixture in your cylinders that can result in a lag before you decelerate; in some vehicles, it can result in unburned fuel sent out through the exhaust.

Port or Multipoint Fuel Injection (MPFI)

This system simply moved the injectors further down towards the cylinders. A separate injector nozzle is devoted to each cylinder, right outside its intake port. That is why some people refer to this system as port injection. Shooting the fuel vapour this close to the intake port ensures that almost all of it will be drawn completely into the cylinder. This system distributes fuel more accurately, with each cylinder receiving its own spray of fuel, this result in better fuel-air ratios. The MPFI virtually eliminates the possibility that fuel will condense or collect in the intake manifold. The downside is that all injectors spray at the same time, while the cylinders fire one after the other. This result in leftover fuel in-between intake periods, or a cylinder firing before the injector had a chance to deliver additional fuel. This systems work great when traveling at consistent speeds, but not when you quickly accelerate or decelerate; it therefore reduces fuel economy and/or performance.

Sequential Fuel Injection (SFI)

Also called sequential port fuel injection (SPFI) or timed injection, this is a type of multiport injection. Recall that in the MPFI system, multiple injectors spray their fuel at the same time or in groups. This downside was addressed through the introduction of the sequential fuel injection, where each injector nozzle triggers independently, matched to your cylinders, allowing the engine to mix the fuel right before the valve opens to suck it in. This resulted in better efficiency and emissions. It also enabled injectors to last longer and remain cleaner than other systems due to fuel not “hanging” around in the chamber. Timed injection is controlled electronically but it can also be controlled mechanically. Because of these advantages, sequential systems are the most common type of fuel injection in vehicles today.

Direct Injection

Direct injection takes the fuel injection concept about as far as it can go, injecting fuel directly into the combustion chambers, past the valves. Even though more common in diesel engines (because the fuel is so much thicker and heavier), direct injection is starting to pop up in petrol engine designs, sometimes called DIG for direct-injection gasoline, where it is almost exclusively used in performance vehicles. Because these vehicles operate with very precise parameters, it is especially important to maintain the fuel delivery system; fuel metering is even more precise than in other injection systems.

That wraps up our quick look at the different injection types mainly found in vehicles. Let us move on to the part where we learn how to identify any injector related problems.

Know and Troubleshoot common Fuel Injector issues

We hammered on this in every other article, and we will continue doing so: the most common causes of component failure, is poor maintenance and general wear and tear. Preventive care is critical when it comes to vehicle maintenance. The problems posed by a faulty fuel injector, should be shared, and as soon as you are familiar with these problems, then the easier it will be for you to diagnose a problem and address it swiftly. After all, you acquired your vehicle for the main purpose of moving between points A and B, and if you either do not possess the diagnostic skills or if you procrastinate on rectifying the problem, then this moving between points A and B will be brought to a dead standstill. If you consider that the injectors are part of the fuel supply system, then you should know that problems with the fuel injectors can cause all sorts of engine performance issues, and these issues may render your vehicle non-functional. Let us therefore look at the most common problems associated with fuel injectors.

Engine misfires and decrease in power, acceleration, and fuel efficiency

According to the yourmechanic website, engine performance issues are one of the most common symptoms of a failing fuel injector. An upset in the fuel-air ratio of the engine may attribute to such performance problems. A faulty fuel injector can cause the vehicle to misfire, to lose power and acceleration, and even to a reduction in fuel efficiency. In severe cases, it can cause stalling or it can prevent the engine from running at all. Have you heard of an engine surge? If the fuel injector sprays too much fuel into the cylinder, this will create a surge in the engine and acceleration will be slower. If an insufficient amount of fuel needed for combustion is supplied, it will place more demand on the injector to supply it with sufficient fuel. When this happens, you can wave your fuel economy good bye.

Dirty & Clogged Fuel Injectors

Fuel additives that do not spray into the intake manifold or combustion chamber can leave a residue on the fuel injectors. These can burn and form a crust because fuel injectors run very hot due to the friction produced. The crust on the fuel injectors can result in a weak spray and an uneven pattern. Fuel injectors can also clog from the build-up of microscopic foreign objects, which are usually in the form of rust. Debris or impurities in the fuel may also contribute to this clogging of the injector. A clogged fuel injector will not be able to supply fuel to the intake manifold or combustion chamber.

Ian Swan (2015) makes an important observation in this regard. Whenever an engine powers down, the combustion chamber have leftover fuel “hanging” around. While the engine cools, the vaporized gases settle on every surface in the combustion chamber, including the fuel injector nozzle. Over time, this residue can reduce how much fuel the injector can deliver to the engine. To reduce this, he suggest that you should let the engine cool down a little before shutting it off. This must be what the “Know your parts” website refers to as HEAT SOAK. They say that when the engine (not the vehicle) stops, the fuel residue evaporates in the injector nozzles, leaving waxy olefins behind. Because the engine is off, there is no cooling airflow moving through the ports and no fuel flowing through the injectors to wash it away, so heat bakes the olefins into hard varnish deposits. Over time, these deposits can build up and clog the injectors. They also warn against dirty injectors in turbocharged engines that can have a dangerous leaning effect, and that may lead to engine-damaging detonation. When the engine is under boost and at a higher rpm, it needs all the fuel the injectors can deliver. If the injectors are dirty and cannot keep up with the engine’s demands, the fuel mixture will lean out, causing detonation to occur. The leaning out may cause higher than normal exhaust temperatures and turbo failure.

Fuel odour

Pro Car Mechanics (2018) points to the fact that the strong smell of fuel in your vehicle may be a sign that your fuel injector is failing. Occasionally, the high-pressurized system of the injector can cause fuel to leak around the connection points of the mechanism. Keep an eye out for any fluids accumulating beneath your vehicle.

Fuel Injector Does Not Open or Close

The valve in the fuel injector might not open as the result of faulty windings or as the result of a rusted fuel injector. The windings might overheat, short out, or break, and rust can cause the valve to stick. In any of these instances, the valve will not open and the fuel injector will be unable to deliver fuel through its nozzle. The valve in the fuel injector might also be unable to close due to a faulty spring or due to a build-up of rust or fuel additives. If the valve is unable to close properly, the fuel injector will leak fuel.

Check Engine Light illuminates

As with most of the other vehicle components, the illuminated Check Engine Light could indicate a faulty injector. A clogged injector or an electrical issue will set off this light. Remember that there are many other reasons apart from the injector that may illuminate the Check Engine Light.

Fuel Injector Leaks

If the mechanism that must cool the injector fail, then the injector can overheat and fail, resulting in a leak. According to the “Know your parts” website, a leaking injector will cause the rail to lose pressure while the vehicle is sitting resulting in a longer than normal crank because the rail will need extra time to pressurize.

Not Enough Resistance – Solenoid

Khair & Jääskeläinen (2013) says that most fuel injection systems use electronics to control the opening and closing of the nozzle. Electrical signals are converted into mechanical forces using some type of actuator, either electromagnetic solenoids (as can be seen in the animation – the one turning red and blue) or active materials such a piezoelectric ceramics. What do you think will happen if something goes wrong with this component? The “Know your parts” website also points to the fact that the solenoid creates a magnetic field that pulls up the injector pintle when the injector is energized. The magnetic field must be strong enough to overcome the spring pressure and fuel pressure above the pintle. If it is not strong enough, the injector may not open all the way, thereby interfering with performance. Short or excessive resistance in the injector solenoid can also cause similar problems.

These then are the symptoms to be on the lookout for, and in the event of any of these manifesting itself, address it. Sometimes an injector fault can easily be remedied, but mostly it will require trained mechanics and technicians to address this. Have an injector balance test done to isolate a faulty injector, or the voltage changes from the O2 sensor checked. Even the pressure loss in the fuel rail can be measured with an electronic injector pulse tester to isolate the problem. At Steves Auto Clinic, we have the means and the expertise to address any injector problems that may arise. Bring your vehicle to the leader in the automotive servicing and repair industry, bring your vehicle to us. We care.

Sources consulted during the writing of this article:
• Bruzek, J. (2016). What Are The Different Types of Fuel Injection? Online available at: https://www.cars.com/articles/what-are-the-different-types-of-fuel-injection-1420690418419/ Accessed on 31 July 2018.
• How a car works. (Undated). How a fuel injection system works. Online available at: https://www.howacarworks.com/basics/how-a-fuel-injection-system-works Accessed on 29 July 2018.
• Khair, M. K., Jääskeläinen, H. (2013). Diesel Fuel Injection. Ecopoint Inc, Dieselnet.com, Canada. Online available at: https://www.dieselnet.com/tech/diesel_fi.php Accessed on 29 July 2018.
• Know your parts. (Undated). When To Replace A Fuel Injector. Online available at: https://www.knowyourparts.com/technical-resources/engine/replace-a-fuel-injector/ Accessed on 29 July 2018.
• Pro Car Mechanics. 2018. Easy tips to diagnose a faulty fuel injector. Online available at:  https://procarmechanics.com/easy-tips-to-diagnose-a-faulty-fuel-injector/ Accessed on 29 July 2018.
• Shedheads. (Undated) Best fuel injector cleaner/types. Online available at: https://shedheads.net/best-fuel-injector-cleaner/types Accessed on 31 July 2018.
• Swan, I. 2015. What Causes Fuel Injectors to Get Clogged or Dirty? Online available at:  https://www.yourmechanic.com/article/what-causes-fuel-injectors-to-get-clogged-or-dirty Accessed on 29 July 2018.
• Wikipedia. 2018. Injector. Online available at: https://en.wikipedia.org/wiki/File:Injector3.gif Accessed on 29 July 2018.
• Yourmechanic. (Undated). How to Diagnose a Bad or Failing Fuel Injector? Online available at: https://www.yourmechanic.com/article/symptoms-of-a-bad-or-failing-fuel-injector Accessed on 29 July 2018.