Kinsler_Handbook_#32 December 2017

Kinsler Fuel Injection, Inc, 1834 THUNDERBIRD TROY, MICHIGAN 48084 U.S.A. Phone (248) 362-1145 Fax (248) 362-1032 120 ELECTRONIC FUEL INJECTION BASICS GROUP FIRED This injection system generally triggers a group of the injectors simultaneously. The ignition system or crank trigger provides the signal to the electronic control unit (ECU) for speed input and thus injector triggering. Since a V8 ignition fires four cylinders per revolution, this gives four injections per revolution on a basic group fired system... eight injections per engine cycle. Most ECU’s can be programmed to fire the injectors based on the number of ignition/trigger inputs received. Example: a typical V8 engine will be programmed to pulse 4 or 8 injectors every fourth input pulse from the ECU trigger device. The good thing about the group fired system is it’s low cost. The problem is that while some injectors will be close to properly timed, others will not. If an injector is triggered at the wrong crank angle, fuel may collect in areas of the intake port or cling to the runner walls. When the intake valve opens, only a portion of the fuel injected will be in suspension with the air entering the cylinder, while the remainder may be running down the port wall as liquid. This can cause erratic mixture conditions to exist in that cylinder, especially during low speed engine operation, due to the small amount of air movement in the intake runner. Many engines have at least some liquid fuel coming past the intake valve at various conditions. One saving grace is that the pressure drop and turbulence across the intake valve causes much of the liquid fuel to become atomized at that point. Since EFI injectors turn on and off, the interrupted flow causes pressure waves to bounce around in the fuel rails, especially at wide open throttle where the flows are the highest. In a group fired system you often trigger two or more injectors at a time in a given fuel rail. The simultaneous pulses can reinforce each other at some RPM to give unusually high pressure pulses, sometimes causing poor fuel distribution. It often helps to run a larger diameter fuel rail. Our extruded aluminum fuel rails are .680 inch inside diameter as this smooths out the pulses quite well when compared to smaller sizes. Running higher overall system pressure also helps. We often run about 72 PSI instead of the more common 36 to 45. The amplitude of the pressure spikes will remain about the same, but will be relatively smaller based on the percent change in injector flow. We also like the better atomization achieved with the higher pressure and it sometimes gives better power and economy. Be careful about running too high of fuel pressure, as some ECUs don’t have enough current to lift the disc or pintle in the injector consistently off the seat against this added pressure, resulting in poor fuel distribution. Also be sure your fuel pump is capable of supplying the engine with the volume required at this higher fuel pressure. SEQUENTIAL FIRED These systems trigger each injector at a precise crank angle on every cylinder, usually near top dead center overlap (intake valve opening). This improves idle quality, low speed engine smoothness, and fuel economy. Some systems can even be programmed for different injection phasing for each speed site in the fuel map. Triggering a sequential system is more complicated than a group fired system, as it requires a separate triggering signal to refer- ence the start of the injector firing sequence. This signal is typically generated once every two crankshaft revolutions on a 4 cycle engine and is most commonly referred to as the “CAM” or “SYNC” signal. The sequential system also requires a “Crank” signal, generated at a specific crankshaft angle on each cylinder. This signal is used to calculate engine RPM and crank angle position for injector firing and ignition triggering from the ECU. “Crank” and “CAM” signal requirements will vary with each manufacturers ECU. Most manufacturers require either a sine wave signal, typically generated by a magnetic sensor, or a square wave signal, typically generated by a Hall effect sensor. Electronic fuel injection metering, when properly designed and programmed, is today’s most accurate way to introduce fuel to an internal combustion engine. With it’s many sensors and input signals it can be tuned to meet the demands of an engine operating over an extremely broad range of conditions. The most commonly sensed inputs are: The magnetic pickup is a simple magnetic material core wrapped with fine wire. When a piece of steel is passed by it, a electric pulse is generated. This pickup may not give as nice a signal as the Hall effect, but it can operate in a much hotter environment and it is more rugged. The Hall effect square wave signal is generally very stable at all RPM and produces a very clean sharp signal wave. A problem with the Hall effect is that it has a solid state computer “chip” inside of it, so it cannot be surrounded by air that is hotter than 300 o F, or the chip may fail. 1) Engine RPM 2) Throttle position and rate of opening/closing 3) Barometric pressure and/or manifold absolute pressure (M.A.P.) 4) Air temperature 5) Water and/or oil temperature, and sometimes fuel temperature There are two basic types of multi-port EFI : 1) Group Fired 2) Sequential Fired Accel DFI Gen. VII system We offer a complete line of both group and sequential fired systems, priced from approximately $1,500.00 for the base grouped fired unit to $18,000.00 for the most sophisticated sequential system for the professional racer. © 2017