Fuel Injection Service Today
By Jim Linder and Doug Garriott
Troubleshooting fuel injectors requires knowledge of common
conditions associated with these electronically controlled valves.
After many years in the fuel injection business we still learn a little more each and every week. We thought we knew fuel injection many years ago when we wrote one of our first manuals for Allen Testproducts on the 1979-80 EEC-3 systems that we all became so fond of back then. But as time went on, we found we actually knew very little about these systems as changes were being made each and every day. Even now, as we process thousands of fuel injectors each month, we still learn something new with each barrel we process.
Linder Technical Services has written many other articles for AutoInc. in regard to fuel injection operation and service both on and off the vehicle. I suggest reading these articles. They are found at www.lindertech.com under "What's New."
When we receive a phone call in our injector lab in Indianapolis, the call will be concerning a fuel injector service problem. Usually the customer would like a set of fuel injectors for a given vehicle or engine application. These units are needed based on a number of conditions:
- Normal maintenance based on high mileage or another engine service requiring the removal of the injectors.
Discussion: Some shops find it as a benefit to their customer, when doing high-mileage maintenance, to go ahead and replace the injectors instead of doing an "on-car cleaning." This ensures that the injectors are operating at 100 percent and that the seals and filter are new. A local delivery service uses Ford vans and replaces the injectors as part of their extended service when the vehicle has high mileage and requires an engine replacement. It is much easier to handle an injector replacement when the new engine is going in the vehicle.
- Lean engine operation, based on codes and other testing or due to engine modification.
Discussion: An injector becomes lean (low fuel flow) either because there was contamination in the fuel system or it is dirty at the discharge end. Both of these conditions are a larger problem today than a few years ago due to a number of issues such as:
- Contamination of the fuel system happens more often than you may think. Either someone has deliberately put something in the tank or the customer bought some contaminated fuel. System parts may come apart as well (tank float, etc.).
Remember: Some fuels don't have as much detergent as others to help keep the system clean. If you suspect contamination, take a fuel sample and let it set overnight. Sometimes more then a few hours are needed to get any contaminants to separate. When contamination is found, a complete system flush is needed, including cleaning the tank, new filter and installing a flow-matched set of injectors.
- Smaller orifices in the injector spray tip. The actual spray diameter has become much smaller on many models as each manufacturer looks for better atomization of fuel to improve emissions and fuel mileage from their fleet. This means the injector doesn't have as great a margin for restriction before there is a problem. Some of these smaller orifices also create a directional spray and any restriction could send fuel away from the valve.
- Returnless fuel systems create another situation. Approximately 20 percent of total vehicle emissions come from just raw fuel handling hydrocarbons (HCs) ppms. Each manufacturer is now handling HC emissions with sealed and closed fuel systems. The returnless fuel system becomes almost standard on today's vehicles to control evaporation emission. Since there is no return line back to the tank, any contaminates that make it out of the tank usually end up staying in the rail. These will settle in the injector filter and restrict the fuel inlet. They will also restrict the fuel flow through the rail and can cause other injectors to go lean. With a returnless fuel system, it is a good idea to clean the rail when replacing the
- Discharge end protection has almost become a thing of the past. If you look at an injector from 20 years ago, you will notice that it has a pintle cap or recessed discharge area. This protected the discharge port and helped it stay clean.
Many of today's injectors have an exposed discharge or just an o-ring retainer at the discharge end that provides no protection to the discharge ports. This allows carbon (coking) to build up and restrict the fuel spray. Depending on the engine, as little as 6 percent flow decrease can set a misfire code. Many times an intake cleaning will help prolong discharge end clogging and should always be done before installing a flowed-matched set of injectors.
- Engine modifications that create a lean issue is just due to a lack of homework. It only stands to reason that if you add a device that is going to enable more or better airflow you need to add more fuel. Some people are under the impression that the computer can compensate for these changes. This is not necessarily true; if the modifications are mild, then maybe an adjustable pressure regulator will work. If major work was done, the injector flow rate needs to be looked at. Here is a quick formula that can be used to find what lb/hr injector is needed.
Injector Flow Rate =
Horsepower x Brake Specific Fuel Consumption/
No. of Cylinders x Max. Duty Cycle
BSFC calculated values are 0.4 - 0.8
Max Duty Cycle is considered at 0.8 (80%)
- Rich engine operation based on codes and other testing.
Discussion: The causes of lean engine operation mentioned could also cause a rich condition. If dirt or some other foreign material gets in the injector, it could keep it from seating properly, and this would allow fuel to drip when the injector is supposed to be off. This foreign material may have passed through the fuel system or formed at the discharge end. You may be able to find this problem by isolating the injectors and observing a fuel pressure loss.
- Injector mechanical failure occurs when the injector is not opening.
Discussion: While we don't see many injectors actually wear out, they do stick from time to time. This is usually due to contamination and the tips mentioned earlier should be used. Mishandling during removal can cause mechanical failure. If the discharge tip gets broke or brute force was used to remove the injector from the engine, odds are the injector may not function properly if reinstalled. If injectors sit around the shop for an extended period of time while service is being done, they could stick.
- Injector electrical failure is common with some injectors.
Discussion: There are some injectors that are known for their coil windings shorting out or even going open. Many theories are out there as to what caused the winding to fail. Some of these are just myths, like the fuel or the cleaning chemical used during a fuel injector cleaning came in contact with the winding, causing them to fail.
This isn't true because the windings are on a bobbin and the fuel passes through the center of the bobbin, and is never in contact with the windings. Injectors are like any other electrical device and may fail. Sometimes we see this only during short pulse width commands. Due to a slightly lower than normal resistance within the injector, the magnetic field (or magnetic induction) buildup is not strong enough to lift the needle of the seat. The injector may work normal when the pulse width command is increased.
Different makes and models have pattern failures, and these failures do occur each and every day. While some models never break, others break often just based on a poor design from the manufacturer!
- O-Rings and seals failure can be either internal or external.
Discussion: From time to time, internal seals (under pressure) will fail from heat and movement. This will cause injectors to leak fuel externally. The most common area is to have fuel leak where the metal body meets the plastic connector. Another area is where the discharge tip is fitted into the body.
Although not as common, fuel can come through the electrical connector if the internal o-ring deteriorates. External o-ring failure will either cause a vacuum leak at the intake or fuel leak at the rail. Pay close attention to where the fuel is leaking. Many times, what is thought to be an external o-ring leak at the rail is really an internal o-ring allowing fuel to leak at a seam.
Jim Linder is owner of Linder Technical Services, an automotive technician support facility in Indianapolis. For more information on these topics, call (317) 487-9460, or visit his Web site at http://lindertech.com.
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