How does a fuel injector work?
A fuel injector is nothing more than a high-speed valve for gasoline. An engine computer or controller is used to control the fuel injector. Contrary to popular belief, this is NOT done by sending power to the injector. Fuel injectors are normally fed power whenever the ignition key is on. The computer controls the negative, or ground side, of the circuit. When the computer provides the injector with a ground, the circuit is completed and current is allowed to flow through the injector. This energizes an electromagnetic coil inside the injector, which pulls a sealing mechanism (pintle, ball, or disc) away from its seat. This makes it possible for fuel to flow through the injector and into the engine. When the computer removes the electrical ground to the injector, the electromagnetic coil becomes demagnetized and a spring forces the pintle, ball, or disc shut to cut off fuel flow. Even at an engine speed of just 1000 RPM, this is done hundreds of times per minute.
What do the terms "static” and "duty cycle” mean?
An injector in an engine turns on and off very quickly to control the amount of fuel delivered. The amount of time an injector is turned on and delivering fuel is known as the duty cycle. This is measured as a percent, so 50% duty cycle indicates that the injector is held open and held closed for an equal amount of time. When the engine needs more fuel, the time that the injector stays on (its duty cycle) increases so that more fuel can flow into the engine. If an injector stays on all the time, it is said to be static (wide open, or 100% duty cycle). INJECTORS SHOULD NOT GO STATIC IN A RUNNING ENGINE! If an injector is static in a running engine (open 100% of the time), that injector is no longer able to control fuel delivery. It is just "along for the ride”. This could be an indication that the injector is too small for the needs of the engine. Injector duty cycle should usually not exceed 80% in a running engine at any time.
What is impedance?
Impedance is the electrical resistance of the electromagnetic coil inside the injector. This is measured in ohms and can be determined with an ohmmeter. Injectors are classified as either high-impedance (also known as "saturated”) or low-impedance (known as "peak and hold”). High-impedance injectors usually range from 11 to 16 ohms of impedance, while low-impedance injectors usually range from 0.7 to 5 ohms of impedance (these impedance numbers are based on what is currently available in the consumer market and are subject to change). Most OEM engine computers are designed to control high-impedance fuel injectors. Low-impedance injectors are generally preferred for racing or ultra-high performance use because they respond more quickly, but aftermarket engine controllers are usually required to control them.
What is an injector’s static flow rate?
Manufacturers rate fuel injectors by the maximum amount of fuel that they can flow in a given amount of time. This measurement is taken with the injector on 100% of the time (100% duty cycle, or wide open) and with the fuel at a given pressure (usually 43.5 psi). For example, a 19 pound per hour (Lb./Hr.) injector flow 19 pounds of fuel in one hour at 100% duty cycle and 43.5 psi of fuel pressure. Injectors in imported vehicles are often rated in cubic centimeters per minute (cc/min) instead of pounds per hour. This is also done at 100% duty cycle.
If injectors should not exceed 80% duty cycle under operating conditions, why do manufacturers rate them at 100% duty cycle?
A test at 100% duty cycle is used to determine the maximum amount of fuel that will flow through an injector in a given time. This test is useful for determining whether an injector’s internal fuel passages were machined properly, but it does NOT check an injector’s ability to cycle on or off. It is usually NOT recommended to run an injector at more than 80% duty cycle under actual driving conditions. This 80% duty cycle operating limit is taken into account to make sure the injector will be large enough to feed the engine under ACTUAL OPERATING CONDITIONS and will not starve the engine for fuel.
Does Marren Fuel Injection remanufacture fuel injectors?
No. As part of our fuel injector service, we clean and test a customer’s injectors and replace the serviceable components (o-rings, inlet filters, etc.) We do not modify or alter any of the internal components of the injector. These internal components (windings, pintle, etc.) are usually not serviceable. If they are damaged, the injector should be replaced.
Does Marren Fuel Injection alter injectors to increase their static flow rates?
Absolutely not. It is sometimes possible to increase an injector’s static flow rate at a given pressure by machining or enlarging the pintle or internal passages of the injector. However, this procedure is usually not a good idea! A fuel injector cycles on and off thousands of times per minute to feed an engine the proper amount of fuel. Because of this, the electromagnetic coil and pintle of an injector are very carefully matched to one another. Modifying the pintle or other portions of the injector may cause it to flow more fuel at its limits (wide open or statically), but at lower engine speeds the injector will be extremely inconsistent. This creates drivability problems, idle fluctuations, higher emissions, rich/lean conditions, etc. We have performed extensive laboratory tests on many modified injectors and have yet to find one that performs as well as an unmodified injector of the same capacity.
Does Marren Fuel Injection offer used injectors on an exchange basis?
No. In our opinion, the ONLY advantage to offering injectors on an exchange basis is a reduced turn-around time for parts. Here is an example of how an exchange sale works: A customer sends in a set of eight injectors with approximately 80,000 miles of use. When the injectors are received, eight injectors with the same flow rate are pulled out of a bin, placed in a box, and shipped back to the customer. The process is very quick, but the customer never knows exactly what he or she is receiving. Since there is no way to tell how many miles an injector has been in service, our hypothetical customer, who sent in a set of injectors with 80,000 miles, may get back a set with 250,000 miles that are much more likely to fail. In our opinion, most exchange injectors are little more than junkyard parts that have been cleaned up, and purchasing a set is a gamble. In order to eliminate the guesswork, we prefer to test and clean a customer’s injectors. Our average turn-around time is 1-2 working days (not including shipping), which is usually quick enough for most customers. We can even accommodate rush jobs for an additional fee.
What is included in Marren Fuel Injection’s Injector Service?
When an injector arrives at Marren Fuel Injection, it is tested to see if it functions properly. Its flow rate and fuel spray pattern are checked to determine if it is working properly, and its impedance is tested. The injector is then cleaned and flushed, and any serviceable parts, such as o-rings, seals, and plastic pintle caps, are replaced. After this, the injector is re-tested to note any improvements in performance due to the service. All of the measurements and information gathered during testing is recorded on a computer analysis sheet that is shipped to the customer along with the injector. When multiple injectors are provided, the injectors are also checked against one another to make sure that they are matched in performance.
Why does Marren Fuel Injection flow test injectors at a controlled pulse-width instead of wide open (static)?
Manufacturers usually rate injectors by their static flow. A static flow test is done with an injector energized 100% of the time and is used to find out how much fuel can physically flow through an injector in a given time. This test will determine if the pintle or sealing mechanism of the injector was machined properly, but it does not indicate how an injector will cycle or control fuel under actual operating conditions. Marren Fuel Injection fires the injector at a 6 millisecond pulse when checking flow numbers because it tests both the mechanical and electrical functioning of an injector. To perform this test, the injector is flowed at a 6 millisecond pulse rate. The results are then compared to the data found in our injector performance database. This test will indicate any electrical problems that an injector may have as well as any machining errors that may be present. We consider a 6 millisecond controlled-pulse test to be more precise than the tests performed by the original manufacturer.
