An engine will not perform at its best without the proper air/fuel mixture.Fuel Injector Cross Section The fuel system of a modern computer-controlled fuel injected engine is so reliable that it seems to be almost maintenance free, but these modern fuel injected engines have fuel injectors that become flow restricted or “dirty” with use. When supplying a customer with a new set of fuel injectors, flow check them to make sure they are all flowing within 2-3% of one another. If the flow rate varies by too much from injector to injector, the engine will cause drive-ability ­problems. As the fuel injectors get dirty, there will be a gradual loss of drive-ability and power. Not all injectors will get dirty at the same rate, so drive-ability can be lost in this way too.


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Dirty Fuel Injector

Diagnosing the Fuel Injection System

The use of a scan tool is the best way to diagnose the fuel injection system. Even if you do not have the latest scan tool, there are many low-cost computer scan tools on the market that are very affordable and easy to use. The long-term fuel trim data obtained from a diagnostic scan tool can be used to read how much the computer is adjusting the fuel injector pulse width so the engine has the correct average air/fuel mixture. When the fuel injector flow becomes flow restricted,Fuel Injector Flow Varience Test the computer will attempt to adjust the fuel flow by opening the fuel injector longer through the use of its long-term fuel trim function. If the long-term fuel trim reading from the scan tool shows the computer is correcting the air/fuel mixture by more than 10%, the fuel system is in need of diagnostic attention. The engine will perform its best when the computer does not continually have to correct for fuel injectors that are not supplying the proper volume of fuel the engine needs.

Cleaning the Fuel Injectors

If the fuel injectors are restricted or leaking, there are several options to clean them including:
1. A fuel injector-cleaning chemical that is poured into the fuel tank.
Provides a noticeable difference in power and drive-ability after one use. The disadvantages are that you can’t check the spray pattern, and the filters may become plugged with contaminants freed by the cleaner.
2. A cleaner that runs through the fuel rails and injectors.
Uses stronger chemicals that the in tank cleaners. Same disadvantages as 1.Injector Flow Bench In Action
3. An ultrasonic injector cleaner and injector flow bench.
The preferred method of cleaning injectors. Cycles the fuel injectors while the fuel injector tips are immersed in an ultrasonic bath, which uses an environmentally friendly cleaning fluid to clean the fuel injectors. The flow bench portion also allows a user to perform a flow test before and after cleaning, and it allows the user to observe the fuel injector spray pattern. This method requires that the fuel injectors be removed from the engine.

Checking Fuel Injector Flow

Injector Filter Size
The flow bench can simulate any rpm or load condition while the technician can observe the spray pattern. Ideally, all fuel injectors would be built to the same flow tolerances, but that would increase the size of fuel injectors substantially. Most OE fuel injectors are held to a +/-2% variance, but aftermarket ones can be as much as 25% from the target flow rate. The fuel injectors should always be replaced as a set unless you are confirming the replacement injectors flow volume and spray pattern are the same as the original injectors by flow testing them on a fuel injector flow bench.

Preventing Dirty Fuel Injectors

Ultrasonic Cleaning Bath
Using gasoline that is infused with detergents to clean the fuel injectors while the engine is running. Some of these products even have formulations to help protect the fuel system against the corrosive effects of sulfur that is commonly found in today’s gasoline. These harmful sulfurs can corrode the fuel level-sending unit in the tank and cause the fuel level gauge to malfunction.

The CNG Alternative

CNG or Compressed Natural Gas is an alternative fuel in place of gasoline. Clean and Dirty Fuel Injector FiltersBecause CNG is clean burning, CNG vehicles have much lower maintenance costs then gas powered vehicles. CNG injectors are much higher flow than regular injectors, but they use the same tiny filters. CNG filters tend to get very dirty over time and can cause damage in extreme cases.

The Clean Advantage

When all the fuel injectors are flowing the correct amount of fuel to each cylinder, the engine performance will be at its best supplying the vehicle with maximum power and fuel economy. Fuel injector maintenance and service is a very important part of proper vehicle maintenance. Choose the fuel injector cleaning method that works best for you, and don’t forget to change the fuel filter. Henry Olsen Jr., also known as “Professor Drivability” is part owner and operator of Ole’s Carburetor and Electric, Inc., located in San Bruno, CA. Ole’s Carburetors is a complete auto parts store that offers “off the car” carburetor, fuel injector, starter, alternator and generator rebuilding services. Additionally, Ole’s Carbs offers “on the car” fine tuning of fuel and ignition systems. Visit them at

Related articles:

  1. When To Replace A Fuel Injector
  2. Understanding Electronic Fuel Injection
  3. Clean Fuel Tanks and Filters Save Pumps
  4. Lean Fuel Condition – P0171
  5. Fuel Pump Diagnostics Using Scan Tools