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HPBG: Engine Builder Fuel Injection Maintenance

Even a perfect engine will not perform like it should unless each cylinder has the correct air/fuel mixture the engine needs.

By Henry P. Olsen

Page 1 of 2

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.