How to Test Fuel Injectors

Have you ever gone to an auto repair shop for regular scheduled maintenance and they said you needed a fuel injection service? When this happens the first question should be why do I need this. But in order to have an educated conversation with the shop about the fuel system it would be helpful to learn more about injectors and how to test them for problems.

Three Tools for Testing Fuel Injectors

The mechanic that is selling a fuel system service should certainly have the three tools needed to properly diagnose any problems in the system. These tools would include a pressure gauge, balance tester and a noid light which is a specialized low voltage LED test light that analyzes the computer driver side responsible for opening the injector on a modern automobile.

To explain how these tools are used we’ll start off with the pressure gauge. This is essential for diagnosis because modern cars use high fuel pressures that range from 35 to 70 PSI or more. As time goes on automobiles have been increasing the amount of pressure in the fuel lines that lead to the injectors. This tester can be used in several locations to test different components. Most commonly there is a line tap that is used to check the output of the fuel pump. Some vehicles will have an additional line tap after the fuel pressure regulator so that testing can be done closer to the injectors.

The fuel injector balance tester is another useful tool a qualified repair center should have on hand. This is used in conjunction with the gauge mentioned above. The tester manually triggers each injector one time to see how much fuel flows through it. It’s a simple timing device that holds it open for a set amount of time usually measured in milliseconds. The idea is each one should reduce the line pressure by the same amount or at least close to it. Each vehicle will have specifications of what the line pressure should be and how much each injector should flow. These tests usually have a passable range of plus or minus 3 PSI (pounds per square inch).

The noid light will be used on under performing or completely inoperative injectors to test the computer drivers on modern vehicles. A noid light kit will come with several different size connectors to match the different automotive manufacturers. The electrical connector is disconnected from each one and the light is inserted into the harness side. The engine can be either cranked over or restarted for a short time and the light should flash each time the injector is triggered by the on board computer.

Do I Need a Fuel Injection Service

In all fairness most shops will just recommend this as a preventative maintenance service. In these cases cleaning the fuel injectors is not intended to solve any problems such as rough running or poor fuel economy. If a service is recommended and the shop states that it will cure a problem, consumers should ask more questions about how the shop reached this conclusion.

If a mechanic or shop tells you they tested each individual injector and a problem was detected you can ask more about the tools they used while conducting this test. It should include at least two of the three mentioned above. If a single injector was identified as being clogged this should have been confirmed with a balance test. Often cleaning will not solve any flow problem and the component might have to be replaced.

Car owners should attempt to access automotive technical service bulletins issued from the car manufacturer to see if there are any recognized common problems with that type of fuel system. The evolution through the years of electronic fuel injection has pushed some questionable technology onto the automotive consumer. Stating this in another way, let’s say some fuel injectors are more likely to experience problems than others. Generally speaking the newer the vehicle the more likely trouble-free operation will be.

When someone states you need to have the injectors cleaned it would be wise to start asking questions of why the automobile needs this. Questioning the shop about the tools they have on hand to diagnose such problems is also an excellent question to put forth. Automotive consumers should be on guard when promises are made that the service will increase performance or fuel economy. This is especially true if you’re just in for an oil change and aren’t experiencing any problems or check engine lights. This service is often up sold as a benefit to the auto repair center instead of the car owner.