Understanding the E-TEC Fuel Injector by Bill Grannis
Containing few moving parts the simple but unique E-TEC fuel injector propelled Evinrude to being the award-winning low-emission outboard leader
in the marine industry. In fact the Environmental Protection Agency (EPA) bestowed its prestigious Clean Air Award to Evinrude, a first for any outboard motor manufacturer.
Unlike an automotive fuel injector which is basically an electrically operated open-shut valve, the E-TEC injector is a self-contained pump that delivers a precise amount of fuel for complete combustion and full power output. This enables Evinrude to be exceedingly emission friendly in addition to boasting a quiet, smokeless, and economical experience that rivals 4-stroke outboard motors.
To understand how the fuel delivery is regulated, think of an empty measuring cup held under a kitchen faucet. If you turn the faucet on for exactly one second, a specific amount of water flows into the cup. If you hold the faucet on for two seconds, then twice the quantity of water is delivered . On the other hand, if you hold the faucet open for only 1/2 second, subsequently half the volume enters the cup. It is the same principal for the E-TEC injector but the “on times” are measured in thousandths of a second.
For the sparkplugs to ignite the fuel injected into the combustion chamber , there must be tiny atomized droplets of gasoline surrounded by air in the vicinity of the sparkplug gap. Larger droplets of atomized fuel inside the combustion chamber are required for greater power output and piston cooling at higher throttle settings. “The strength and duration of the injection pulse determines the fuel droplet size,” says George Broughton, then Director of Engineering, “which varies to meet the unique needs of the engine”.
The E-TEC injector first builds up internal pressure before dispensing its fuel charge into the combustion chamber of the cylinder head and that is the “magic” behind the E-TEC process. The injector is similar to a hypodermic syringe. If you hold a syringe in your hand and press steadily on the plunger with your thumb, a stream of liquid will squirt out approximately a distance of two feet. Now if you use a hammer to hit the plunger with a hard blow, it will cause a shock wave inside the syringe body with an instantaneous increase in pressure, forcing the liquid stream to spurt out perhaps ten feet.
As the impact-shock pressure rapidly intensifies inside the injector housing, a spring-loaded nozzle opens causing the liquid fuel to break up into a super-fine spray. The nozzle design is similar to a garden hose sprayer. As you rotate the brass body on the sprayer, the nozzle shape and the water pressure outputs a finer and finer mist.
To better understand how the E-TEC injector operates, visualize a hypodermic syringe attached to a garden-sprayer nozzle with a hammer at the other end in which to strike the plunger. In a nutshell, this is exactly how E-TEC injectors work, but it uses an electrical solenoid and a moving plunger as the “hammer” to produce the shock wave.
An E-TEC injector assembly uses a pulse of electricity through its moving-coil windings to contact the poppet valve (plunger) generating a rapid spike in fuel pressure due to the impact shock . The resulting high-pressure surge forces the spring-loaded nozzle open which in turn atomizes the liquid gasoline into a microscopically fine mist. The duration in which the injector is electrically activated determines the volume of fuel delivered into the combustion chamber. It will pump twice the amount of fuel if held on for 2/1000ths of a second as compared to being energized for only 1/1000th of a second. The longer the injector is fed electricity, the more fuel enters the cylinder. Timing and duration is regulated by the Engine Management Module (EMM), a powerful onboard computer. For more information about an EMM and how it works, click HERE.
During manufacturing each injector is thoroughly tested for its flow characteristics and given a serial number that contains calibration numbers called coefficients. These numbers “tell” the engine computer (EMM) how to compensate for slight differences in flow so that each electrical pulse to the injector will be timed to deliver a precise amount of fuel, measured in millionths of a gallon. These unique numbers are the reason that the injectors cannot be used in a different cylinders or on another engine; the injector’s coefficients and cylinder location are programmed into the EMM. It is the combination of the EMM and the calibrated injectors that makes the Evinrude E-TEC an ultra-low emission outboard as determined by the EPA and the California Air Resources Board (C.A.R.B.).
For an example of the fuel metering accuracy, a V6 E-TEC idles around 500 rpm and consumes about 0.3 gallons of gasoline per hour. That means that it takes 3.3. hours to consume 1 gallon and in that time the engine completes 99,000 revolutions activating the 6 injectors on each rotation. The calculations show 594,000 injector pulses for every gallon of gasoline. In other words, the E-TEC injector has to be extremely accurate to deliver less than two/millionths of a gallon per cylinder each time it “fires”. For those who live by numbers, that equates to approximately 0.0000017 gallons of gasoline for each injector activation.
Because of the injector’s highly technical design and precision construction it is important to have a quality fuel-water separator filter in addition to the engine-mounted fuel filter. Today’s ethanol E-10 fuels attract moisture which may settle to the bottom of a fuel tank and be ingested into the motor’s pumps and injectors. Be proactive by using fresh gasoline in the tank and a fuel stabilizer additive such as Evinrude’s 2+4 to avoid gummy varnish deposits and to help prevent corrosion. This way your motor will remain the reliable, smooth running outboard that it should be and give you years of enjoyment on the water.