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Basic installation and adjustment guidelines for autogas systems, part IV

02.06.2017

The correct installation of the autogas system is only half of the success of preparing a car for trouble-free driving on gas. The next step is skillful adjustment. As it was mentioned earlier, the controller is responsible for the whole process of autogas control. If it's configured incorrectly, it will not be able to calculate the correct gas dosing for the full range of the engine operation. A poorly adjusted system may cause problems whilst the engine is running on gas. It is not the fault of autogas components, such as the reducer or injectors, but the fitter who does not adjust the system properly due to a lack of knowledge or sometimes a lack of willingness. In the case of STAG controllers, system adjustment requires AcGasSynchro or AcStag application (depending on the system type) and an interface for communication between the computer and the controller. After the connection of the STAG controller, the application is started and it detects communication automatically. The application is started with the default window for parameters. Set the option before autocalibration is started. On the right side there are the parameters of the engine and autogas components. If any of the presented parameters are incorrect (erroneous reading of the temperature, rpm speed, etc.), it is necessary to find and eliminate the cause before autocalibration is started. Configure the controller presets in the first tab. The article will not discuss all the available options in the tab, as some of them are obvious and respective descriptions can be found in the controller manual. I will try to focus on the most important ones. The tab with parameters is split into two larger segments: parameters of the vehicle and settings of the gas controller. The former is used to enter basic car data, such as the number of cylinders, engine type, Lambda probe type, etc. The second allows the settings of gas controller operation to be entered, i.e. the temperature of switching to gas, selection of injectors or maximum rpm speed on gas. The tab with parameters also includes options that are used only in special cases. Another useful, or rather essential, option in some cars is the threshold of cutting off extra-injections. Engine control functions include the so-called extra-injections, i.e. the very short injection of additional petrol (lasting for example 0.5 ms) occurring between normal injections of petrol. The available gas injectors are not able to handle such short injection pulses in practice. Then the "extra-injection cut-off threshold" is used, after which the controller does not consider any signals below the value that is set, e.g. when 1ms is set, extra-injections of 0.8 ms are ignored by the controller. Entering the information in the Parameters window is the first step to complete; then go to the autocalibration tab. This is the first setting of the controller on idle. Some inexperienced fitters only use this function of the controller calibration. They think that the completion of this process is all that is required of them and the customer leaves the workshop in the mistaken belief that the car has been adjusted properly. I would like to stress the fact that the autocalibration option only adjusts the controller when idling, not under all loads. After the successful completion of the process the message "Set the multiplier in a test drive" appears, which should give food for thought about the following steps. The setting of the multiplier requires a laptop and an assistant to drive the vehicle. When the "Map" tab is activated, the chart "Multiplier" is displayed on the left hand side and MAP pressure on the right vertical axes and "Petrol injection time" on the horizontal axis. Autocalibration brings up the curve for initial multiplier settings (yellow). The points set on the line are used to adjust the gas dose depending on injection pulses. A question arises: how can we know that the air-to-fuel mix is too rich or too lean within a specific load range? During the test drive, the controller acquires the points from the petrol map and gas map and arranges them on the map as a green line (gas) and blue line (petrol). The acquisition of both maps should be made in the same conditions. Decide the course of acceleration, gear shifting, etc., and generate both maps by following the same routine. Generating the maps under different loads will result in the incorrect adjustment of the multiplier, if the fitters make the settings based on the maps. A more precise method is to make the configuration based on injection time and experimenting with petrol/gas switching in both ways. Observe petrol injection pulses in specified points and switch to gas, then check if the petrol injection time goes up or down. If the pulses get longer, increase the point on the multiplier representing pulse setting and if they get shorter - lower the point. If the point is set correctly, the petrol injection time should not change after switching to gas. Adjustments based on the STFT and LTFT values are even more precise, but these require a scanner to read and record the measurements. For Q-Box Plus, Q-Next, Q-Max STAG-300 Premium, the scanner is not required, as these controllers are equipped with an integrated OBD adapter. Corrections in most of the cars should be kept close to "0". If they tend to take negative values, the mixture is too rich, if they take positive values, the mixture is too lean. Checking the corrections for petrol fueling first and then setting the multiplier based on those values is recommended. Switch to gas and observe the trims. If they go below zero, reduce the point on the multiplier curve, if they go above zero, raise the multiplier point step by step until the correction is close to zero under a certain load. When adjusting the system it is also important to observe the reducer. If the reducer is sufficient for the power of the engine, it should maintain a relatively stable gas pressure under sudden acceleration. Pressure drops can be present but they should not exceed 0.2 bar. When higher drops occur, start to consider replacing the reducer, or, adding a second one. During calibration it is important to observe Lambda probe signals as well. Check the performance of the probe particularly during sudden acceleration. The probe should indicate a rich mixture then. If the value is close to the lean mixture, identify the cause. This can be caused by high pressure drops in the reducer, insufficient size of the injector nozzles or the insufficient output of the injectors. Making the mixture richer with t the multiplier adjustment may be all that is needed.

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