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What Is a Fuel Injector Balance Test?

In order to work, an internal combustion engine requires four elements, air, fuel, compression, and spark. Broadly speaking, it could be said that the diagnostic process of a vehicle consists of determining if one or more of those four elements is not reaching the expected values.

In this article, we will focus on one of such elements, the fuel. Specifically, we will be talking about what is a fuel injector balance test, and the different ways to perform it.

Fuel Injector Test

Fuel Injector Balance Test, What Is It and What Is It Used For?

The fuel injector balance test is a procedure that measures the amount of fuel delivered by each injector. This measurement can be done directly or indirectly depending on the method used.

You have probably heard, or even witnessed, how mechanics perform a compression test on an engine. A compression test reveals the condition of your engine’s valves, its valve seats, and piston rings, among other things. Similarly, the fuel injector balance test verify the general condition of each individual injector. Moreover, through the fuel injector balance test, technicians can pinpoint critical issues such as:

  1. Faulty fuel injectors (due to an internal failure)
  2. Faulty or loose fuel injector electrical wiring connection
  3. Air leaks through the fuel injector lower seal
  4. Electronic Control Module fuel injector driver failure
  5. Other failures not directly related to fuel injectors (air, cylinder compression, or spark)

How many of these tests can be performed and what information they return will largely depend on the type of injector balance test the technician performs.

Types Of Fuel Injector Balance Tests

Depending on the year, model, and make of the vehicle, the technician may perform different types of injector balance tests.

  •       Pressure Drop-based Injector Balance Test. Popular on pre-2000 vehicles, usually performed with the engine OFF. This test consists of measuring the pressure drop on the system each time an injector is activated.
  •       Computer-controlled Injector Balance Test. On newer vehicles (2000 onwards) chances are that the technician might use an automotive scanner to perform a fuel injector self-test with the engine on.
  •       Flow-based Fuel Injector Balance Test. This is the ultimate fuel injector balance test and is the preferred method used here at Mike Carburetor Parts. It consists of using a fuel injector bench to measure the flow of each injector.

Pressure Drop-based Injector Balance Test

This is probably one of the most basic injector balance tests out there. It can be done using a fuel pressure gauge in conjunction with an automotive scanner or a fuel injector pulse tester.

Basically, the technician disables the vehicle’s ignition system and then connects a fuel pressure gauge. Next, the technician pressurizes the system by turning the ignition key to the ON position but without starting the engine. With the system pressurized, the fuel pressure reading is taken. After that, the technician activates each injector individually, either by using the Special Functions of the automotive scanner or the fuel injector pulse tester. The pressure drop caused by the injector activation is measured then. Once an injector is tested, the ignition key is turned OFF and then ON again to get ready for the next injector.

The procedure is repeated for each injector, once at a time. Once finished, all readings are compared. The greater the pressure drop, the greater the contribution of the injector to the fuel supply. In other words, if any of the injectors do not show a pressure drop (or its pressure drop is very small) then it is assumed that said injector has a problem.

Although this method is fairly simple and does not require removing the injectors from the vehicle, it does have several limitations:

?      The fuel flow is measured indirectly, through the pressure drop. Due to errors associated with the gauge, fuel lines, electrical system, fuel pump activation, and others, this method is one of the least accurate of all.

?      In many cases, an injector showing too little pressure drop can be related to problems in the injector wiring, which in turn can lead to misdiagnosis.

?      The diagnostic procedure is time-consuming and extremely cumbersome.

Computer-controlled Injector Balance Test

Given that is relatively easy to perform, this is a popular method used by dealership and auto repair shops alike. All it takes is a vehicle-compatible automotive diagnostic scanner.

The test consists of using the special functions of the scanner to access the “Fuel Injector Balance Test”. In most modern vehicles, this test can be carried out automatically or semi-automatically with the engine running. In automatic mode, the scanner instructs the vehicle’s computer to turn off each injector individually. The drop in engine speed is recorded automatically and at the end of the test, the results are displayed on the screen. The semi-automatic mode is very similar, with the difference that the technician chooses which injector to turn off and for how long. Generally, in semi-automatic mode, no value is recorded, so the technician must take note of the engine speed drop manually.

In comparison to the pressure drop procedure, this method is really fast and straightforward. However, it has its limitations too:

?      The “Fuel Injector Balance Test” is a program loaded into the vehicle’s computer, not the scanner. Which means that not all vehicles support this feature.

?      Even if the vehicle is compatible with the automatic injector balance test, the measurement of the fuel flow is still indirect, since it is done through the drop in engine speed. Moreover, the engine speed is one of the worst points of reference, as it is tremendously inaccurate and is subject to other engine issues (for example, a spark plug failure directly affects engine revs).

All in all, this is a quick test, that can give the technician a general idea of cylinders performance more than actual fuel injector issues.

As mentioned before, this method consists of using an injector test bench to perform the balance test. One of the main differences between this method and the previous ones is that the injectors must be removed from the vehicle in order to be tested. This, which at first may seem like a disadvantage, is what gives this method its greatest advantage. Isolating the fuel injectors from the rest of the engine systems.

Using a bench to perform the fuel injector balance test has several advantages over the rest of the methods described above:

?      The flow is measured directly at the injector nozzle. Meaning that unlike indirect measuring methods, fuel pressure, electrical connector issues, fuel rail design, and fuel leaks will not hinder accuracy. Furthermore, using a fuel injector bench for the balance tests is the closest you can get to real fuel delivery measuring.

?      Fuel injector benches can simulate different engine speeds by changing the injector’s pulse width. This feature enables technicians to identify injector problems at idle, cruise, or high speeds. No other method can achieve that.

?      This is the only method that can effectively “aisle” fuel injectors from any other issue present on the engine.

?      Aside from performing flow-based fuel injector balance tests, EFI benches allow technicians to run other types of injector diagnostics such as spray pattern tests, and injector leak tests.

The high accuracy provided by this particular method is what motivates the experts at Mike Carburetor Parts to recommend the use of a specialized injector test bench to perform all of these tests.

Updated on 05/05/2021

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