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By Dave Worden EFI Update I n a previous series of articles on Electronic Fuel Injection (EFI) in OPE, I covered basic terminology, open loop and closed loop operation and all of the acronyms associated with EFI systems. As you may recall, I also combined the systems used by Kawasaki (open loop) and Kohler Engines (closed loop). In this update, I will cover some additional changes and features used in the Kohler EFI system. The original Kohler EFI system had the following components: Intake Manifold, Battery Ignition Coil, Throttle Position Sensor (TPS), Engine Temp Sensor, Fuel Injector and an Electronic Control Unit (ECU). It also had an Oxygen Sensor that helped it to go to closed loop. Two newer components that will be incorporated in this system are as follows: Manifold Absolute Press (MAP) and Inlet Air Temp (IAT). Review of an open loop system Let's review how the open loop system operates in its most basic form. The ECU monitors primary sensor signals and compares them to pre-programmed "maps" to manage fuel delivery and spark. A "map" is a predetermined amount of fuel and air to be ignited based on starting and running conditions. It then tries to achieve the ideal mixture dependent upon the throttle position and load. Closed loop operation To go to a closed loop operation, you add an oxygen sensor in the exhaust system and tie it back to the ECU. Based on information supplied back to the ECU by the various components, the ECU adjusts the fuel and spark to get the "ideal" burn and run more efficiently and effectively. To accomplish this, the Engine Temperature Sensor tells the ECU that the engine has warmed up sufficiently; memory in the ECU will adapt and store running information. 22 Figure 2 — Throttle Position Sensor (TPS) Throttle Position Sensor (TPS) The Throttle Position Sensor (TPS) is Figure 1 — Electronic Control Unit (ECU) Component review The ECU is the brains of the system. It reads and configures all the other components and gets them to work together to achieve the ideal burn for efficiency. The unit has the following capability: internal memory features (resettable) and three hour meters (1 for current run time, 1 for permanent time, and 1 for trip meter). The ECU also controls maximum rpm; maximum voltage; maximum temperature; intake air temperature; engine temperature (oil/ coolant); and the rev limiter, which will cut fuel delivery if the engine exceeds 4,500 rpm (see Figure 1). the primary detection of acceleration and secondly monitors throttle position as a way to detect load. Think of it as a variable resistor. If removed or damaged, it resets. Refer to the service manual for procedure (see Figure 2). The other thing to keep in mind is that the engine must be in a "Steady State," which means the engine is not accelerating or not starting. The ECU needs to run in a rich mode when it is cold just for starting. Once the engine goes into closed loop operation, it has an adaptive learning process and tries to learn its environment. One piece of additional information is that the unit will go to "short-term" adaption once the engine is warmed up to 140 degrees Fahrenheit (60 degrees Celsius). When the engine reaches 176 degrees F (80 degrees C), long-term adaption begins. Sequential injection (What is it?) To be able to be truly fuel efficient, another feature to add is sequential injection. That is, the spark ignites only for the power stroke (no waste spark). Injectors only operate during the intake stroke. Batch fire is used during start-up below 600 rpm. Sequential injection (How it works) The speed sensor locates the missing tooth on the flywheel to indicate the crank position. The MAP sensor then identifies a sudden pressure drop located near the cylinder head to indicate the proper stroke and then controls the spark and fuel to accomplish the function. Figure 3 — Oxygen Sensor Oxygen Sensor The Oxygen Sensor uses a catalyst OUTDOOR POWER EQUIPMENT www.outdoorpowerequipment.com