![]() ![]() This is one of the reasons for Honda excellent idle and part throttle characteristics in all conditions. The ECU uses this information to make small fuelling adjustments at altitude. This sensor tells the ECU at what altitude you are running. For example one Hondata customer using 830 cc injectors in a B20 turbo has drivability indistinguishable from stock and achieves 30mpg. We have found Honda ECUs work particularly well with larger injectors. Larger injectors with a heavier pintle also take longer to open and close due to inertia and show a similar effect. Another reason to keep low fuel pressures. Increase your fuel pressure and the extra fuel line pressure can slow the injector opening. The difference is most noticeable at small injector durations - part throttle. With poorer quality transistors the injectors do not open or close as quickly, resulting in less fuel delivered in the same amount of time. Hondas switch the injectors on and off rapidly (red line). All Honda ECUs drive high impedance injectors or low impedance injectors with an external resistor box. These transistors do not even get warm (except when low impedance resistors are incorrectly wired in without the Honda resistor box!). These are excellent quality transistors, which make a substantial contribution to how the well the Honda ECU drives injectors. Analog Output: Injector driver transistors This is where the 12V signals are conditioned and converted into 5V for processing - such as the distributor signals TPS and MAP. No other vehicle maker we are aware of uses a backup processor and this level of redundancy. This is military specification redundancy designed to keep you going even in the event of multiple sensor failures. Limp home mode is rev limited to 3500 RPM with a fixed ignition and rather rich fuel setting with the engine check light permanently on. In fact you can remove entirely the ROM and primary microprocessor and your Honda will still run. ![]() TDC (top dead centre from the distributor) and TPS (throttle position). In this mode the ECU needs only two sensors to run. In the event of a serious failure it takes over the running of the computer in what is called limp home mode. The backup microprocessor monitors the function of the main microprocessor, ROM and sensors. This tech article looks at the functions of the ECU and how it differs from some of the piggyback and standalone systems available. The Honda ECU, like your Honda engine, is a very well designed piece of equipment made to work in many cars under many varying conditions of temperature and altitude. ![]()
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