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 injectors that become flow restricted or “dirty” with use.
This means that if you expect the engine you build to perform like it should, the fuel injectors should be cleaned and flow checked before they are installed. If you are supplying your customer with a new set of fuel injectors they should be flow checked to be sure they all flow within 2 to 3% of each other. If the flow rate varies by too much from injector to injector the engine will cause driveability problems.
The symptoms a driver will most often experience, as the fuel injectors get dirty, will be a gradual loss of engine driveability and power. These symptoms may appear so slowly with time and miles of driving that you may not even notice the loss of power and driveability.
The fuel injectors will become flow restricted from both the deposits that the gasoline leaves in them as it flows through the injectors and carbon deposits that form on the head of the injectors. High underhood temperatures that are common after the engine is shut off will also cause deposits to build up in the fuel injectors as the fuel boils in the injectors when you shut off the engine.
These deposits will both distort the fuel injector’s spray pattern and restrict the injector’s ability to supply the engine with the correct volume of fuel that the engine needs. The deposits will not always form equally on every fuel injector so you can also find driveability issues due to one or more cylinders not getting as much fuel as the other cylinders.
Unless all the fuel injectors supply each cylinder with the correct amount of vaporized fuel the engine will not perform as well as it should, plus it will produce a higher level of exhaust emissions than it should.
Diagnosing The Fuel Injection System
The use of an automotive computer diagnostic scan tool is the best way to diagnose the fuel injection system. Even if you do not have the latest diagnostic scan tool, there are many low cost computer scan tools on the market that are very affordable and easy to use.
Scan tool companies such as OTC/SPX offer low cost scan tools from the OTC # 3111 Code Connect to mid-price range tools such as the OTC Nemisys to the state-of-the-art OTC Pegisys/PC Scan tool systems.
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, 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. Fuel injectors that are flow restricted will need to be held open longer than fuel injectors that are flowing properly.
If the injectors are leaking fuel, the computer will adjust the amount of fuel coming from the injectors by subtracting fuel through the 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 flow restricted or leaking there are several different options available to clean the fuel injectors. These options include:
1. A fuel injector-cleaning chemical that you pour into the fuel tank can be used to clean the injectors. We have had very good results using an in-tank fuel injection cleaner such as Techron Concentrate Plus from Chevron. It is common for a vehicle owner to feel a noticeable increase in driveability and power after just one tank of gasoline treated with the fuel injection cleaning solution in the tank.
The disadvantage of the in-tank fuel injector cleaning method is that the fuel “filter” found in most port fuel injectors may become plugged with contaminants that can be washed into it, plus this method does not allow you to check the spray pattern and flow volume of the fuel injectors. If the in-tank injector cleaning method does not give you the desired results, you may need to try another cleaning method.
2. A second chemical cleaning method is to use a cleaner that is run through the fuel rails and injectors. This method allows a stronger mix of cleaning chemicals than you should put into the gas tank (the stronger mix of chemicals could possibly damage to the fuel system).
This cleaning method can do a good job, but again it does not allow you to check the fuel injector spray pattern, plus the fuel “filter” built into the fuel injector may become plugged with contaminants that are washed into it.
3. Our preferred method for cleaning fuel injectors is with an ultrasonic injector cleaner and injector flow bench such as the ACE/ASNU unit from ACE Fuel Systems that we use. But there are several other companies such as Launch Tech USA, GB Remanufacturing and Walker Products that also offer fuel injector flow bench systems.
The ultrasonic cleaning method involves cycling 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 is more labor intensive because it requires that the fuel injectors be removed from the engine and installed on a test fixture to perform the testing procedure.
Checking The Fuel Injector Flow
A fuel injector flow bench can be used to check the actual flow from the fuel injectors at any load condition or engine RPM (fuel injector on-time) you chose to simulate. The flow bench also allows the user to observe the injector spray patterns, and you can also measure the fuel flow from each injector so the user can be sure the injectors are truly flow matched.
Ideally, every new fuel injector would be built to the same flow standards but holding a production line to that precise of a tolerance would raise the cost of the fuel injectors substantially.
Most new original equipment fuel injectors are held to a +/- 2% production flow variance, but some inferior replacement injectors that you buy at your local auto parts store may not hold to the same tight flow standards.
Also, due to part number consolidation, some injector suppliers sell fuel injectors with a flow rate that may vary as much as 25% from the flow rate of the OEM injectors that the engine’s computer is programmed to work with.
If the fuel flow and spray pattern is not the same from each fuel injector used on an engine, the air/fuel mixture delivered to each cylinder will vary. When the air/fuel mixture varies by more that 6-8% from cylinder to cylinder the engine will have cylinders that are running too rich and cylinders that are too lean.
When a cylinder does not have the correct air/fuel mixture the engine’s power output, drivability and fuel mileage potential will suffer.
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 flowing them on a fuel injector flow bench.
GM’s Multec fuel injectors that were used in its Tuned Port fuel injected engines produced from 1985 through the early 1990s had some known issues. The insulation on the fuel injector coil windings deteriorated and then allowed the injector coil to short circuit as the gasoline caused the insulation to breakdown.
The problems you may experience can vary from an occasional one-cylinder miss (caused by an intermittent short in the injector coil) to a totally dead cylinder (a short in the injector coil that no longer supplies any fuel to the cylinder).
Preventing Dirty Fuel Injectors
The best preventive medicine to help prevent fuel flow restricted injectors is to tell your engine customers to use a gasoline that has detergents in it to help keep the fuel injectors clean and prevent deposit formation before it becomes a problem. Many of the car manufacturers recommend the use of a gasoline that conforms to the new “top tier” gasoline standards to help keep the fuel injectors clean.
“Top tier” gasoline has detergents in it that will help keep the fuel injectors clean as you use it, and many of the major gasoline brands are now being blended to these higher standards. The level of detergents in “top tier” gasoline is not always strong enough to keep your fuel injectors clean, so from time to time your customers may need to add some extra cleaning power to their fuel.
The use of an in-tank fuel injector cleaner such as Chevron’s Techron Concentrate Plus at the same mileage schedule as you change your engine oil is a very good way to be sure your fuel injectors stay clean. A dose of Techron Plus will raise the level of detergents in a tank of gas by about 10 times what it is in a typical “top tier” gasoline.
Techron Concentrate Plus is one of the best in-tank fuel injector cleaners we have used, and the “plus” is that it helps 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 most common symptom of a corroded fuel level-sending unit is a fuel level gauge that may stick or not read the correct level of fuel in the tank. The corrosive effects of sulfur may also create excessive wear to the electric fuel pump(s) that are in the gas tank and thus shorten the fuel pump service life.
The CNG Alternative
CNG or compressed natural gas is an environmentally friendly alternative fuel source in place of gasoline because CNG is a very clean burning fuel. CNG powered vehicles have lower maintenance costs than gasoline powered vehicles but they still need service. The fuel injectors that are used with CNG are much higher flow than the same engine would use with gasoline but it still uses the same tiny filter that a standard fuel injector uses.
Some of the CNG injectors we have serviced have had filters that are much dirtier than any other injectors we have serviced. I have been told that this problem is mainly seen Northern California, but if you work with CNG powered vehicles it would be wise to keep an eye on the injector filters.
The debris that flows thru the fuel system and the oil vapors from the CNG compressor can cause fuel injector flow problems as the filter becomes restricted. The fuel injectors can become so flow restricted that engine damage may happen in extreme cases.
It would a good idea to have the fuel injectors cleaned and flow tested on a fuel injector cleaner/flow bench whenever a CNG powered engine or vehicle is in the shop for a tune-up or rebuild.
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.