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How to Test Fuel Injectors – What You Need To Know!

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How Does The Fuel Injector Work?


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In order to know how to test fuel injectors, it is key to know the signs and symptoms of a bad, damaged, or failing fuel injector to know how much the price of the fix will be and the steps of the fuel injector test. 


As we know, the fuel injector’s basic function in your vehicle is to give the engine enough fuel to run properly and at a high performance. The fuel injector injects the fuel into the engine’s cylinder through a specific tube, or nozzle, so that the internal combustion process can begin to power the engine. 


  • Fuel Injector Function


To make sure the engine works correctly, the fuel must be delivered at the proper time and must be injected in the right amount. In addition to the timing and the amount of fuel, the fuel injector has to determine the right pressure, angle, and spray pattern to ensure the engine runs smoothly. When looking at how to test fuel injectors, you need to know the fuel injector’s function with your engine. 


  • Fuel Injector Mechanism


The engine control unit is your car’s computer and manages components like the fuel injector, telling it how to work, how much fuel to give, and when to give the fuel. By using various sensors in the car’s electrical and fuel system, the electronic control unit has to make sure that the injector gives the fuel at the right time and in the right amount to create the ideal air to fuel mixture and ratio. 


If the electronic control unit is not working correctly, this can increase the cost of the fuel injector replacement cost and cause you to have to learn how to test fuel injectors. 


The car’s fuel pump is in charge of pushing the gasoline from the fuel tank, through the gas lines and into the fuel injectors that are in charge of supplying the engine. When the electronic control unit can read and analyze what fuel is needed to give to the engine, it gives this information to the fuel injector solenoid. 


The fuel injector solenoid opens in order to allow the pressurized fuel to spray into the cylinder. If the fuel injector is not working correctly, you need to learn how to test fuel injectors. 

Faulty Fuel Injector Symptoms


The faulty fuel injector in your vehicle can prevent enough fuel from being given to the engine in order to power the car, or it will incorrectly time the interval at which it is supposed to deliver the fuel. No matter what the case is, your vehicle will not be able to run correctly, or it will not be able to run at all, causing you to need to know the steps of how to test fuel injectors. 


  • Rough Engine Idle


Since your vehicle will not get enough fuel to run properly or even to run at all, the RPM while your engine is running will drop way below the normal and the optimal levels. This can even result in a rough engine idle in your car, where the car will be unnecessarily vibrating and shaking while staying still. If the engine RPM is too low, the car could actually stall and cause you to need to restart the voice. 


A rough engine idle can be a sign that the fuel injector replacement cost will be higher and cause the need to learn how to test fuel injectors in your vehicle. 


  • Engine Vibration


If your fuel injector is faulty or damaged, this can cause the engine cylinder to not be able to fire at the right time or prevent it from firing at all. This means that while you are driving your car, the engine will excessively vibrate or shake after it tries to finish the cycle without enough fuel. Without the engine containing enough fuel, the vibrations can increase the need to learn how to test fuel injectors. 


  • Engine Misfiring


If the engine does not get enough fuel via the fuel injector due to a clogged injector or an injector that is not working correctly, then the engine will begin misfiring as you are driving. Your vehicle will have problems accelerating, especially when trying to reach high speeds or going uphill. In addition, there might be a delay in acceleration after you press your foot on the gas pedal to power the vehicle, causing the need to learn how to test fuel injectors. 


  • Check Engine Light


There are many reasons why your check engine light might turn on. You might have a faulty oxygen sensor, your mass airflow sensor might have failed, or various other reasons that this light can illuminate on your dashboard. Not all of these reasons are severe, but they should require that you get your car looked at by a mechanic. 


In this case, the most obvious sign of a problem with the fuel injector in your car is that the check engine light turns on. If this light illuminates on your dashboard, it means that the fuel injector is delivering less fuel than needed, and the engine efficiency is lowered. If you need to make sure this is the problem before learning how to test fuel injectors, you can use a diagnostic tool and an oBD2 scanner to confirm the problem.


  • Fuel Leak


Another sign that your fuel injector could be damaged and something that could increase the overall fuel injector replacement cost is a fuel leak. If your fuel injector is broken or cracked, gasoline will leak out of the pipe, and the fuel will not reach the engine to power the car. If you check the fuel injector and check for any leaks or cracked pipes, you might notice gas outside or on the nearby fuel rail. 

How To Test Fuel Injectors – Different Methods

Method 1 – Testing TBI Injectors


When trying to learn how to test fuel injectors, you need to know the first method’s steps using TBI injectors to visually inspect the fuel spray. The fuel flow spray is accessible, making it efficient and easy to check for any potential fuel system issues and fuel injectors.


When checking the fuel spray, there are three main steps you will have to undertake. The first step is to remove the cover off the air cleaner housing. Next, ask the assistant to start or crank the engine if the engine does not turn over. Lastly, check the pattern of the spray to see if the fuel injector is not working correctly. 


If the fuel comes out in the inverted V pattern, you have determined that the fuel injector is working correctly. If there is an irregular pattern when learning how to test fuel injectors, an internal part is worn down or damaged. 


Additionally, if you do not see fuel coming out of the fuel injector, this is a clear sign that you have a problem to address. There can be various reasons for this damaged fuel injector, like a blocked injector, damaged injector parts, bad fuel pressure regulator, clogged fuel filter, or a damaged fuel pump. 

Method 2 – Testing EFI Injectors


The second way to learn how to test fuel injectors is to test the EFI injectors by determining which injectors are working within your system and whether the fault is within the fuel injector or within the controlling circuit of your fuel system. 


Unlike the other injectors on the TBI systems in method 1, the EFI injection system doesn’t have the fuel spraying available for easy inspection that can be done in just minutes. For this system, you have to check each injector’s spraying pattern with the necessary and proper equipment. 


To determine the fuel spray when learning how to test fuel injectors, you have to listen to each injector to see if each one is working or not. First, to listen to the fuel injector, you have to use a mechanic’s stethoscope or bring your car to a local auto body shop. 


The next step is to let the engine idle, applying the parking brake, and opening the hood. Next, use the stethoscope on the side of the injector to see if there is a clicking sound. The sound comes from the interior solenoid activating and deactivating the valve of the injector. If you don’t hear the clicking sound, this is a sign that you need to learn who to test the fuel injector to see if it is working correctly. 

Method 3 – Checking Fuel Injector Coil


The third method when learning how to test fuel injectors is checking the fuel injector coil when determining if your fuel injector is dead. One of the tests you can do is use a multimeter, a diagnostic tool, to check the coil’s resistance value. You can analyze the necessary resistance value that is in your car’s service manual. 


You can do this by first turning the engine off. Unplug the fuel injector’s electrical connector and then set your digital multimeter to the correct value for your specific car. Probe the injector terminals to see and analyze the resistance reading. Using an ohm meter or a diagnostic tool can be a great way to learn how to test fuel injectors. 

Fuel Injector Replacement Cost Comparison


When learning how to test fuel injectors, sometimes you discover that your fuel injector needs a complete replacement to continue working properly. In order to get the right price for your fuel injector replacement, you need to compare costs between various shops. 


For certain places that you can get the fuel injector replacement, the prices are quite similar. We have a list of chain auto body shops and your local mechanic to determine which can provide you the best estimate for the fuel injector replacement cost.


Your mechanic will charge you between $193 and $415, while the Midas shop will run a little bit more expensive, between $206 and $437. Mr. Tire is similar in pricing, but is a little bit more expensive at the high end of the price spectrum, ranging between $215 and $515. 


NAPA can offer you a 24-month warranty for the fuel injector replacement cost and will charge you between $231 and $502, while Walmart will charge you just $73 and $264 for just the parts. Similarly, Amazon will average between $79 and $283 for just the parts, with a limited fuel injector warranty. 

Sample Fuel Injector Replacement Costs


Now that you know how much your chain auto body shop and your local mechanic may charge you for this process, it is important to know how much it costs for popular car models on the market today. After knowing how to test fuel injectors, replacing the part at a reputable shop is the next step. 


One of the least expensive cars is both the Ford Focus and the Honda CR-V, both averaging between $190 and $284 and $338, respectively for the total price. The Ford Focus’s labor costs are between $90 and $115, while the CR-V is between $81 and $103, and the Focus parts are $99 and $169, while the CR-V is between $82-$200.


The high end of the price spectrum is dominated by the Toyota Camry, the Nissan Altima, and the Chevrolet Silverado. The Camry has a labor cost of between $162 and $207, while the parts lie between $166-$278, with the total average coming out to $328 and $485. The Nissan Altima runs at around $222-$287 for the labor, while the parts are between $165 and $241, with the total price coming out to between $390 and $528.



When learning how to test fuel injectors, it is crucial to know the fuel injectors’ function in your vehicle, the symptoms of faulty fuel injectors, the different methods of how to test fuel injectors, and the overall cost of replacing this crucial part. 

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