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Chapter 19 Digital Fuel Adjuster A brilliant voltage interceptor that can be used to adjust air/fuel ratios, allow air-flow meter or injector swaps, and even change closed-loop running characteristics! T HE DIGITAL FUEL ADJUSTER that we’re presenting here is a unique beast. Unlike many interceptors that are available commercially, it is low in cost and easy to fit and tune. It also gives fantastic driveability. It is no exaggeration to say that the release of the Digital Fuel Adjuster Specifications Voltage input....................................................any voltage from 0V to +14.4V Voltage output........................ 0V to +1V, 0V to +5V or 0V to +12V plus offset Offset adjustment............... ±127 steps corresponding to 19.6mV for 5V range Maximum offset adjustment......... ± 0.5V on 1V range, ±2.5V on 5V range, ±6V on 12V range (fine resolution mode reduces adjustment range by a factor of 5) Input adjustment points...............1-128 corresponding to 39mV steps from 0-5V for 5V range Input to output response time for offset change.........................................5ms Display update time.............................................................................250ms Step up and down.......................one step per button press or four changes per second if button held Skip offset adjustments............ step up and down with 4 steps per button press or at 16 steps per second if button held 112 PERFORMANCE ELECTRONICS FOR CARS (DFA) is going to cause a revolution in budget engine management modification. Over a year in development and with many hundreds of hours spent designing and building prototypes and testing and tuning on different cars, the DFA is a device with immense capabilities. Don’t be fooled by its apparent simplicity (just one input and one output!). In use, the DFA is so good that more than one expert was left speechless after driving a car equipped with the device! Adjusting Air/Fuel Ratios The DFA can be used in a number of ways – let’s take the most common use first, where it intercepts the airflow meter’s signal. In many cars, the air/fuel ratios are incorrect for maximum power – typically, the manufacturer runs very rich mixtures at high loads to provide a measure of safety if the car is held at siliconchip.com.au Suggested Uses •  Modify air/fuel ratios by inter- cepting the air-flow meter signal •  Modify closed loop running characteristics by intercepting the oxygen sensor signal •  Recalibrate fuelling after air-flow meter swaps •  Recalibrate fuelling after injector swaps •  Overcome boost cuts sustained full throttle for an hour or two. So instead of an air/fuel ratio of (say) 12.5:1 at full throttle/high load, the standard Electronic Control Unit (ECU) will provide a much richer air/ fuel ratio of 10.5:1. In modified cars running the standard management, the air/fuel ratios can be even richer! If these mixtures can be leaned out, power will improve. So what does the air-flow meter signal have to do with this? Well, the ECU decides how much fuel to inject primarily on the basis of the air-flow meter’s signal. When the engine is consuming a lot of air, the air-flow meter’s output voltage will be at the high end of its range. This means that if an air-flow meter’s output signal varies from 1V at idle to 4V at peak power, the signal output in the 3-4V range will need to be changed to lean out the high-load mixtures. Specifically, to lean out the top-end mixtures, these voltages need to be slightly reduced. In this example, all the air-flow meter output voltages below 3V need to remain completely unaltered, while between 3-4V they need to be reduced. However, the voltages between 3V and 4V probably won’t all need to be lowered by the same amount – more likely, the voltage reduction will need to increase as the voltage rises. So 0.5V may need to be subtracted from 4V signals but only 0.25V from 3V signals. Fig.1 shows the type of change that might need to be made – on the graph it’s easy to see what’s needed. The DFA can make these sorts of tuning changes with ease, reducing or increasing just those voltages that need to be altered while leaving the rest of the signal untouched. siliconchip.com.au Fig.1: this graph shows the type of change that needs to be made to the output of an air-flow meter if the air/fuel ratio is to be leaned at only high loads. Note here that at low loads the output is not altered at all, while the high load outputs are altered by an increasing amount. The Digital Fuel Adjuster can make these sorts of changes with ease, in addition to being able to increase the signal output where richer mixtures are needed. Fig.2: the Digital Fuel Adjuster (calibrated in this example to work with 0-5V signals) divides the voltage range up into 128 separate adjustable values called load points. Each load point can have an up or down tuning adjustment applied to it. In this example, the air-flow meter output actually varies between 0.9 and 4.1V, which corresponds to load points 23–105. By looking at the Hand Controller as an assistant drives the car, it immediately becomes clear which load point numbers correspond to the different engine loads. Main Features •  Programmed using LCD Hand Controller (no PC needed) •  Only one Hand Controller needed for multiple units •  Very easy to install and tune •  Can work on air-flow meter, oxygen sensor and MAP sensor signals •  128 voltage steps able to adjusted in 127 voltage up/down increments •  Switchable sensitivity •  When no changes are made, input voltage exactly equals output voltage without any steps •  Interpolation between adjacent adjusted load points •  Superb driveability PERFORMANCE ELECTRONICS FOR CARS 113 The Digital Fuel Adjuster is shown here controlling the idle mixtures of a BMW 735i. The unit is in LOCK and RUN Modes. LOCK means that tuning changes cannot be made, while RUN shows the real-time behaviour of the system. Here the BMW is at Load Point 39 and the output at this point has been adjusted upwards by 8 units to enrich the mixture. What The Jargon Means Using the Digital Fuel Adjuster is easy and understanding it is mostly just a case of sorting out a few terms: DFA – Digital Fuel Adjuster; the interceptor covered here. Interceptor – a device that takes a signal and changes it before sending it on its way. View – the mode where you can scroll your way through the whole map, making changes as you go. Run – the real-time mode where you can see which load point is being currently accessed by the running car To achieve success with this type of interceptor, three primary design characteristics are needed: (1) the number of voltages that can be adjusted needs to be large; (2) each of those voltages needs to be able to be incremented up or down in small steps; 114 PERFORMANCE ELECTRONICS FOR CARS and what changes have been made at that point. Lock – the mode (activated by the toggle switch on the main unit) that prevents tuning changes being made. Load Point – the 128 available points that cover the full range that the signal is working across; eg, from 0-5V. Input – shows the load point. Output – shows the up/down adjustment made at that load point. Interpolation – this refers to the way that the DFA smoothly changes its output between adjacent tuning points. (3) when no change is desired, the input signal must equal the output signal without any ugly jumps. This easy-to-build circuit achieves all those design requirements. The Design The DFA uses two units – a main box that remains in the car at all times and the LCD Hand Controller (see Chapter 17) which allows the tuning changes to be made. The Hand Controller connects to the main DFA unit via a standard DB25 socket and computer cable – it can either be unplugged once the tuning is finished or it can stay in the car to allow the action of the tuning map to be viewed. •  RUN, VIEW and LOCK Modes: both real-time and non-real-time adjustments are possible. This means that if you change the voltage outputs of the air-flow meter while driving the car, you can immediately see how this affects the engine’s behaviour. For example, on the dyno, you can hold the car at one load and then move the air-flow meter voltage up or down for that load point, using an air/fuel ratio meter to show how these changes affect the mixtures. This real time mode is called RUN. You can also use the DFA in VIEW mode; ie, without the engine having to be under load (or even running, for that matter). In VIEW mode, you can siliconchip.com.au Fig.3: install the parts on the PC board as shown here. Use a multimeter to measure the resistor values before mounting them and always double-check the orientation of polarised components. Make sure that you don’t form any solder bridges between adjacent PC board tracks and double-check the board against the parts list, this diagram and photos before powering it up. This is the view of the completed prototype which was housed inside a standard plastic instrument case. siliconchip.com.au PERFORMANCE ELECTRONICS FOR CARS 115 How It Works The Digital Fuel Adjuster uses a PIC16F628 microcontroller (IC1) to provide the features necessary for such a complex unit. It monitors the input voltage and is then able to alter the output voltage according to the voltage shifts that have been programmed in. The microcontroller also drives the display unit in the Hand Controller (which is used for programming) and monitors the switches. The input signal is applied to pin 2 of op amp IC1 which is connected as an inverting buffer with a gain of -0.5, as set by the ratio of the 470kΩ feedback resistor and the 1MΩ input resistor. IC1a has a high input impedance so that it does not load down the input signal. The 1nF capacitor across the 470kΩ feedback resistor ensures that noise and any signals above 338Hz are attenuated. The signal at IC1a’s output (pin 1) is thus inverted and will be about -2.5V for a 5V input. This means that the signal is divided by a factor of two (2.13 to be more precise). IC1b inverts this signal again and its gain can be set from -0.09 (attenuating) to -11 (amplifying), depending on the setting of trimpot VR1. This enables the circuit to be used with inputs ranging from 0 to +12V, 0 to +5V or 0 to +1V, to provide an output from 0 to +5V. This 0 to +5V range is required for the following analog-to-digital converter (ADC) stage based on IC4. ADC Function IC4 converts the signal applied to its pin 2 input into a digital data stream, as required by microcontroller IC3. This data appears at pin 6 and is fed to IC3’s RA0 input at pin 17. IC3’s RA1 and RA2 outputs provide the chip-select (CS-bar) and clock (CLK) signals to pins 5 and 7 of IC4, respectively. The RA3 and RA4 outputs (pins 2 & 3) of IC3 control the offset adjust circuitry. This consists of a DAC0800 digital-to-analog converter (IC5) and two up/down counters (IC6 & IC7). IC6 and IC7 are connected to produce an 8-bit up/down counter which drives the digital-to-analog converter (DAC), IC5. Initially, pin 11 (the load input) of both IC6 & IC7 is at ground and the 116 PERFORMANCE ELECTRONICS FOR CARS preload input values at the A, B, C & D inputs set the counter outputs. In this circuit, all preload inputs are at ground except for the most significant count input (D) of IC6 which is pulled high (to +5V). This loads a digital count of 1000 0000 into the 8-bit counter and sets the output from the DAC (IC5) and IC2a to 0V. This is the default value when IC3 is making no changes to the input signal. IC5 uses a 9V reference voltage from REG2 to ensure its output is stable and precise. Its output, at pins 4 and 2, is fed to op amp IC2a which operates as a differential amplifier. This makes the circuit a “bipolar converter”, whereby the output can swing either positive or negative about 0V. As a result, the converter can offset the signal above and below its normal level. OK, let’s summarise the basic circuit operation. If no change is required, the input signal (from the air-flow meter) is first fed to inverting op amp stages IC1a and IC1b, and then fed to pin 5 of adder stage IC2b, where the signal is restored to its original amplitude. On the other hand, if the microcontroller is calling for changes to the input signal, its RA3 and RA4 control lines cause the 8-bit counter’s output to change. As a result, the DAC produces an output voltage and this is processed by buffer stage IC2a to produce the required offset voltage. This is then fed to pin 6 of adder stage IC2b, to produce the required output voltage. VR3 And LK1 Trimpot VR3 allows IC2a’s output to be adjusted so that it is at 0V when the DAC is set to the default condition. In addition, IC2a’s output is fed to pin 6 of IC2b via a 47kΩ resistor or via 47kΩ & 33kΩ resistors in parallel, depending on whether link LK1 is installed or not. If link LK1 is removed, then the signal is connected only via the 47kΩ resistor and this reduces the range that the DAC and IC2a can shift the output of the adder stage (IC2b). Note that this gives higher resolution control of the output voltage but the overall range is restricted and so this link should be installed if large changes are required in the output. Note, however, that LK1 can only be removed on the 0-5V and 0-1V ranges and not on the 0-12V range. Diode D3 acts as a clamp to prevent the output of IC2b from going below 0V. This is done to protect the input to the car’s ECU. The input to output signal path is connected via a double pole double throw (DPDT) relay (Relay1). When the relay is not powered, the input signal is directly connected to the output, bypassing the DFA circuitry. When the relay is powered, it connects the input and output to the DFA circuit. The relay is switched using SCR1 which conducts when triggered at its gate by a nominal 0.8V. A resistive divider across the 12V supply sets the gate voltage on SCR1, depending on the setting of trimpot VR4 (50kΩ). VR4 can be adjusted so that the SCR triggers and turns on Relay1 at around 11V if it is required to switch on when ignition is applied, or at above 12V if it is required to switch on after the engine is running. The 470µF capacitor provides a delay in switching, while LED1 indicates when the relay turns on. The microcontroller operates from a 5V supply and runs at 4MHz, as set by the crystal connected to pins 15 & 16. S1 connects the RA5 input to +5V when lock is not required. When S1 is open, RA5 is pulled low via a 10kΩ resistor and this prevents any adjustment of parameters via the Hand Controller. Hand Controller The external Hand Controller (see Chapter 17) comprises an LCD (Liquid Crystal Display) module and a decade counter (IC1). This counter is clocked by IC3’s RA2 output and when a count of 10 is reached, it is reset by the chip select (CS-bar) signal at IC3’s RA1 output. Counter IC1 in the Hand Controller has 10 outputs which go high in sequence. Each output connects to a switch and if a switch is pressed, it pulls IC3’s RB5 input high (ie, when the output connected to the closed switch goes high). IC3 then recognises which switch is closed and acts accordingly. Fig.4: there are relatively few parts in the circuit because most of the work is done by microcontroller IC3. This also drives the LCD module in the external Hand Controller via a DB25 socket. siliconchip.com.au siliconchip.com.au PERFORMANCE ELECTRONICS FOR CARS 117 flow meter is 0.9V - 4.1V, which corresponds to a DFA load INPUT range of 23-105. You don’t need to worry about air-flow meter output voltages when using the Hand Controller (you just look at the displayed INPUT load points), but this does show the relationship between the INPUT load numbers and what the air-flow meter is actually doing. The Hand Controller Fig.5: the power supply uses two 3-terminal regulators to provide the +5V and +9V rails, while IC8 and its associated parts provide a -8V rail. How It Works: Power Supply Fig.5 shows the power supply. As shown, the switched +12V ignition supply is connected via reverse-polarity protection diode D4. It is then fed to 3-terminal regulators REG1 & REG2 which provide +5V and +9V rails. IC8 (a 7555 timer) is wired as an oscillator and operates at about 1kHz. The square wave output from pin 3 drives Q1 and Q2 which act as complementary emitter followers to drive a negative diode pump comprising D1, D2 and the two 100µF capacitors. The result is a -8V rail which supplies the op amps. scroll through the load points, change the up/down adjustments that have been made, or put in new adjustments. VIEW mode is good for quickly getting major adjustments into the ballpark before fine tuning occurs and for smoothing the output curve. Both RUN and VIEW modes are selected using the Hand Controller. A third mode – LOCK – is selected by a switch on the main unit. It is used when you want to prevent inadvertent changes being made to the map, so LOCK needs to be turned off before you can make any tuning changes. •  Input Voltage Ranges: the DFA can be configured for one of three input voltages ranges: 0-1V, 0-5V and 0-12V. This facility allows it to work with any 118 PERFORMANCE ELECTRONICS FOR CARS voltage-outputting sensor on the car and so gives the DFA enormous flexibility in its applications. There are 128 adjustable load points for each of these ranges. Fig.2 shows the approach for 0-5V signals, the most common signal range. The 128 different adjustment points are called “load points”, because in most applications they will correspond to engine load as measured by the airflow meter. Low number load points (eg, 5-10) relate to low loads, while high number load points (eg, 110-120) correspond to high loads (the actual numbers will depend on the car’s airflow meter signal output range). In Fig.2, you can see that the actual output range of the example air- The Hand Controller is used to input all tuning information and also view the resulting tuning map, both real time and non-real-time. It uses a 2-line LCD, eight “direction” buttons, a recessed RESET button and a RUN/ VIEW button. The Hand Controller functions are shown in Fig.8. To speed up the tuning process, you can jump up or down by four load points at a time by using the black  and  keys. The white  and  keys allow you to move up or down the load range one site at a time. In the same way, the voltage modification keys are also available in single step change () and () and 4-step change ( ) and ( ). Holding down the black pushbuttons changes the values by about four changes per second. Alternatively, by pressing the switch at a rapid rate, the values can be altered more quickly. There is no “enter” key: once you have made the up/down changes to the load points, they are automatically stored in memory. After you have finished tuning, set the switch on the main unit to LOCK and then disconnect the Hand Controller – the tuning map will be retained, even if power is lost. You can also leave the Hand Controller connected all the time if you wish but again the switch should be set to LOCK so that inadvertent tuning changes cannot be made. In LOCK mode, the RUN display continues to work normally, allowing you to watch the action of the map when the car is being driven. A single Hand Controller can be used with multiple DFAs and also with the Digital Pulse Adjuster and the Independent Electronic Boost Control projects (described in Chapters 16 & 21). This means that if you are using extra units, only one Hand Controller needs to be built. When the DFA is set so that input = output (that is, no tuning adjustsiliconchip.com.au Fig.6: when calibrating and testing the DFA, use a 10kΩ pot connected across the power supply to give an adjustable input signal voltage capable of spanning the full 0-12V (make sure that you don’t exceed the maximum input voltage for the range that you’re working in). The input, Test Point 2 (ie, TP2) and output voltages can be measured using a multimeter. ments have been made up or down to the voltages at those load points), the output follows the input exactly, without any step changes in voltage. When you have made up or down tuning adjustments in the voltages, you should always program in a smooth curve – you don’t want a sudden spike or dip as that load point is reached. While the system does interpolate for you, there’s no need to make its job especially hard! A recessed Reset switch is provided on the Hand Controller. When Reset is pressed with a “pointy” tool for around four seconds, all output values are returned to zero change – ie, pressing this button will result in the loss of all tuning values! A successful completion of the reset process is indicated by RESET momentarily appearing on the display. The Display (1). RUN Mode: when set to RUN mode, the display will look something like this (values may be different): OUTPUT +10 (dV) INPUT   21 /RUN/ Remember, in RUN mode the car siliconchip.com.au RESISTOR COLOUR CODES Value 1MΩ 470kΩ 330kΩ 100kΩ 47kΩ 13kΩ 12kΩ 10kΩ 5.6kΩ 5.1kΩ 3.3kΩ 2.2kΩ 1.8kΩ 1kΩ 560Ω 330Ω 10Ω 4-Band Code (1%) brown black green brown yellow violet yellow brown orange orange yellow brown brown black yellow brown yellow violet orange brown brown orange orange brown brown red orange brown brown black orange brown green blue red brown green brown red brown orange orange red brown red red red brown brown grey red brown brown black red brown green blue brown brown orange orange brown brown brown black black brown is running and so the load value (the INPUT) being shown is the one that the air-flow meter is producing at that moment. In this example, the load value is 21. The up/down voltage 5-Band Code (1%) brown black black yellow brown yellow violet black orange brown orange orange black orange brown brown black black orange brown yellow violet black red brown brown orange black red brown brown red black red brown brown black black red brown green blue black brown brown green brown black brown brown orange orange black brown brown red red black brown brown brown grey black brown brown brown black black brown brown green blue black black brown orange orange black black brown brown black black gold brown adjustment made to this load value is also shown – here it is at +10, indicating that at load point 21, the voltage output of the air-flow meter has been boosted by 10 units. Note: (dV) means PERFORMANCE ELECTRONICS FOR CARS 119 The Digital Fuel Adjuster allows air-flow meter upgrades to be made with ease. For example, upsizing a hotwire air-flow meter like this one can be carried out without problems. point 29 the output has been set to -14; ie, the output voltage is being reduced at this point. VIEW mode is easily used to smooth the changes. For example, having a sudden jump like this: Output Input Fig.7: wiring the DFA to the car is extremely simple. First, locate the signal wire that connects the air-flow meter to the ECU as shown at (a). This wire will have a voltage that varies with engine load. Cut this wire and connect the end from the air-flow meter to the DFA’s input as shown at (b). Finally, connect the DFA’s output to the original wire that ran to the ECU, then connect the power and earth and the wiring is finished! Note that all these connections should be made at the ECU. 120 PERFORMANCE ELECTRONICS FOR CARS of the load points and its corresponding voltage adjustment can be seen. In VIEW mode, the display will look something like this (values may be different): OUTPUT -14 (dV) INPUT   29 <VIEW> This mode allows the viewing of each INPUT value (ie, load point) and the corresponding OUTPUT setting. The left/right buttons allow selection of the load point value (from 1 to 128) – ie, they are used to move through the load points – while the up/down buttons are used to change the voltage adjustments at the various load points. Here it can be seen that at Load 0 28 -14 29 0 30 0 31 is likely to lead to a stutter as the engine passes through load point 29 and the mixtures suddenly change. It is better to smooth the changes like this: Output Input “delta voltage”; ie, change in voltage up or down. The load point number can vary from 1 to 128, while the adjustment value can vary from 1 to 127 for voltage increases and from -1 to -127 for voltage decreases. When no voltage change has been made (ie, input voltage = output voltage at that load point), a 0 is shown on the display OUTPUT. Any changes made to the OUTPUT display are also delivered to the output. In this RUN mode, the , ,  and  buttons don’t operate, as the unit is displaying the actual load being experienced in real time. (2). VIEW mode: in VIEW mode, each 0 27 -5 27 -8 28 -14 29 -8 30 -5 31 In this example, leaner mixtures are required around load point 29 and so the load points either side of this point have been blended into this change. This blending is most easily done in VIEW mode. In both RUN and VIEW modes, the DFA continues to provide the output variations – this means that values can be altered while the car is running. You can alter the current value that is displayed in RUN mode or you can alter selected values in VIEW mode. Either way, any changes will be included in the output. (3). LOCK Mode: LOCK mode is set by operating the toggle switch on the main unit. In this mode, LOCK siliconchip.com.au is displayed on the Hand Controller. LOCK mode prevents any tuning changes from being made and so this mode should be used when tuning is finished, whether the Hand Controller is left attached or is unplugged. Map information can still be viewed when in LOCK mode. Construction The DFA has quite a lot of components and wire links on its PC board, so construction should be undertaken with great care. Use a multimeter to measure the resistor values before inserting them in the PC board and always double-check the orientation of polarised components. As usual, it’s vital to follow the parts overlay diagram (Fig.3) and the photos extremely carefully. Make sure that you don’t form any solder bridges between adjacent PC board tracks and double-check the board against the parts list, overlay and photos before powering it up. As mentioned above, to use the DFA, you will also need to build the Hand Controller – see Chapter 17. Calibration Before it is first used, the DFA needs to be set up on the bench. This is a quick and simple process. •  Switch-In Voltage: the DFA can VR4 VR1 VR2 LK2 LK1 VR3 VR1, VR2 and VR3 are used when configuring the Digital Fuel Adjuster for 0-1V, 0-5V or 0-12V signals. VR4 adjusts the battery supply voltage at which the Digital Fuel Adjuster switches in its interception. Link LK1 is removed to put the Digital Fuel Adjuster into Fine mode, while link LK2 is inserted as part of the process of configuring the Digital Fuel Adjuster for 0-12V input signals – see text. be set so that it intercepts the air-flow meter signal when ever power is applied, or intercepts it only after the car has started and is running. The DFA works out whether the car has started by measuring battery voltage. For example, the DFA can be set so that it switches in when its supply voltage reaches 13.8V – a voltage that occurs only when the car is running. Trimpot VR4 sets the voltage at which the DFA switches in its interception. Turning VR4 clockwise sets this voltage to a lower level. For example, turning VR4 fully clockwise will switch on the changeover relay Fig.8: the functions of the Hand Controller, shown in VIEW mode. In RUN mode (ie, real-time display and tuning mode), the word “RUN” is displayed on the Hand Controller and the scroll left/scroll right keys no longer operate. siliconchip.com.au PERFORMANCE ELECTRONICS FOR CARS 121 This view shows a boost gauge, MoTeC air/fuel ratio meter and the DFA Hand Controller on the dashboard of a Maxima V6 Turbo. At the time this photo was taken, the car was running intercooling, a new exhaust, higher boost and a radically revised air-flow meter design that massively increased its flow capacity. Mixtures were successfully tuned with the Digital Fuel Adjuster. (Relay1) quickly when “normal” 12V power is applied. If the DFA is required to start intercepting only after the car has started, set VR4 fully anticlockwise and then with 13.8V supplied, wind VR4 clockwise very slowly until the relay switches over (indicated by LED1). That done, turn off the sup- ply and then re-apply power, checking that the relay stays off when the ignition is turned on (12V supply) but switches on when the car starts (13.8V supply). If switchover is required before the engine starts, wind VR4 clockwise until the relay closes at (say) 11V or less. Note, however, that regardless of This view of the rear panel shows (from left): the LOCK switch which prevents program changes being made, the DB25 socket for the Hand Controller cable, the access hole for signal input and output connections, and the access hole for the power supply connections. 122 PERFORMANCE ELECTRONICS FOR CARS the setting, there will be a short delay before the relay switches, while the 470μF capacitor in series with VR4 charges. If you have a variable voltage power supply, this process is easily carried out on the bench. Otherwise, you can do it on the car (refer to the “Voltage Switch-In?” breakout box for more on this function). •  Fine and Coarse Modes: the DFA has two adjustment modes – Fine and Coarse. Once selected, all tuning must be carried out in the one mode. In standard Coarse mode, the DFA can alter the voltage signal by ±50%. For example, in the 0-5V input signal range, the output can be adjusted by ±2.5V (note that the output is prevented from going below 0V). This adjustment range gives enormous power to change the signal – in fact, much more power than is usually needed. Fine mode reduces the amount that the output voltage can be changed by a factor of 5 (to ±0.5V when the 0-5V input range is being used) but gives much finer control. For example, +6 adjustment at one load point in Coarse mode will require about +30 in Fine mode to achieve the same output. Coarse mode is quicker and easier to tune but doesn’t allow fine control. For normal air/fuel ratio tuning (eg, to alter top-end mixtures or to cater for an air-flow meter or injector swap), Coarse mode is normally quite satisfactory. But where you want siliconchip.com.au Uhh, Ohhhh – A Few Provisos The DFA will only work with voltage signals – some air-flow meters have frequency outputs, so the DFA won’t work with these meters. Basically, if you can measure a varying voltage output from a sensor – and it’s anywhere in the 0-12V range – then the DFA can be used to modify the signal. What if the sensor has an output that doesn’t fall neatly into these increments? If the sensor has a working output range which is from say 2.7V – 5.5V, set the DFA up on the bench to work to 5.5V. In practice, this will mean that load points below about 63 won’t be used (in other words, you will have 65 load points left to work with) but this still gives very small load increments. As with all interceptors, modifying the signal from a load sensor may have some unexpected outcomes. For example, when you intercept and modify the air-flow meter signal, every ECU decision that includes engine load as an input will be altered. Leaning out the mixtures by reducing the air-flow meter output voltage will also simultaneously increase the ignition timing, because the ECU will think that the load is less than it really is. In practice, a slightly advanced timing along with leaner mixtures is a common requirement, so that’s no problem. However, if you make a major change – such as fitting new injectors – the alterations that need to be made to be able to alter the signal over a small range very accurately, configure the DFA for Fine mode. Fine and Coarse modes are selected by Link LK1 – the link is removed to put the Digital Fuel Adjuster into Fine mode. •  Input Signal Calibration: the following steps are all carried out with the Hand Controller connected to the DFA and the system poweredup. (Check that the red LED is on to indicate that the DFA is intercepting – see “Switch-In Voltage” above.) Basically, you need to calibrate the DFA for its intended voltage range. This can be worked out by measuring the signal voltage coming from the sensor that you’re going to intercept. For example, back-probe the air-flow siliconchip.com.au to the air-flow meter signal may be sufficient to cause some unwanted ignition timing outcomes. Always monitor the engine for detonation when making air/ fuel ratio changes. Changes made to the mixtures at loads where the engine is working in closed loop mode (ie, the signal from the oxygen sensor is being used to set the air/fuel ratio, usually to 14.7:1) will usually be “learned around” by the ECU. In other words, if you alter the air/ fuel ratio away from 14.7:1 at low and medium loads, it’s likely that after some kilometres of driving, those changes will have disappeared! By contrast, any radical changes made to the mixtures when the engine is operating in closed loop mode will be retained, because the changes will be greater than the ECU can “learn around”. However, if the battery is disconnected and then reconnected, the engine will likely run badly until the ECU has again learned as much as it can. In short, it doesn’t make a lot of sense to make air-flow meter adjustments for loads when the engine is in closed loop mode. However, it is possible to alter closed loop mixtures by using a DFA on the oxygen sensor signal, with it configured in its 0-1V mode (obviously, only with oxygen sensors that have 0-1V output signals!). The effectiveness of the DFA modifications will also depend on how the meter until you find its output signal – ie, a connection that has a voltage that varies with engine load. Drive the car hard and have an assistant check the range that the meter is working over. For example, if it is 1.4V to 4.5V, you would configure the DFA for the 0-5V range. Calibration of the DFA is straightforward but do it carefully. You will need a digital multimeter to measure the signal input, the voltage at Test Point 2 (TP2) and the output voltage. You also need a 13.8V supply and a 10kΩ calibration pot (used to simulate the input signal). Set the system up as is shown in Fig.6. The calibration procedures are as follows: (a) Standard 0-5V signal input: particular system works. For example, in some cars the air-flow meter is used to set the mixtures only at light loads and in cruise, with full-load mixtures calculated from throttle position, manifold pressure and RPM. Modifying the output signal of the airflow meter in this type of system won’t have much effect on full-load mixtures. In a naturally aspirated car which uses a MAP sensor to determine fuelling, altering only high-load mixtures may be difficult. This is because manifold vacuum will drop to zero when the throttle is fully open – irrespective of whether the revs are at 1500 or 6000 RPM. Modifying the voltage output signal of the MAP sensor will therefore lean the wide-open throttle mixtures right through the rev range. To avoid these situations, before you install the DFA, use a multimeter on the sensor to confirm that the signal varies in a way which is consistent with successful modification. For example, you want to see an air-flow meter signal that varies across the full engine load range. Finally, some air-flow meters have an output signal that decreases with increasing load. The only difference this makes is that low load numbers appear on the Hand Controller at high engine loads and you’ll have to make the voltage adjustments in the opposite direction to normal – otherwise the way in which the DFA is used is the same. (1). Apply 5.0V to the input by adjusting the external calibration (test) pot. (2). Adjust VR1 so that TP2 is 5.0V. (3). Press the Reset button for more than four seconds. (4). Adjust VR2 so that the output is 5.0V. (5). Connect the input to ground and adjust VR3 for 0V output . (6). Re-apply 5.0V to the input and adjust VR2 for 5.0V at the output. (b) For a 0-12V signal input: (1). Adjust the external calibration pot so that +12V is applied to the input. (2). Adjust VR1 so that TP2 is 5.0V. (3). Press the Reset button for more than four seconds. (4). Adjust VR2 so that the output is 12.0V. PERFORMANCE ELECTRONICS FOR CARS 123 Fig.9: this graph shows the changes in values that were made on a 1988 Nissan Maxima Turbo V6, where the DFA was used to tune the mixtures by intercepting the air-flow meter signal. As the car came on boost at Load Point 47, the mixtures were enriched from a near-stoichiometric 14.5:1 to a much more power-friendly 12.9:1, while at high loads (from Load Point 53 onwards), the air/fuel ratio was leaned from about 11.2:1 (typical) to 12.5:1. (Note that this tuning used an earlier prototype version of the DFA which had only 64 load points, not the 128 of the current model). Driveability was excellent – in fact, with the more appropriate mixtures, better than factory. (5). Connect the input to ground and adjust VR3 for 0V output. (6). Re-apply 12.0V to the input and adjust VR2 for 12.0V at the output (c) For a 0-1V signal input: (1). Install link LK2. (2). Apply 1.0V to the input by adjusting the external calibration (test) pot. (3). Adjust VR1 so that the output at TP2 is 5.0V. (4). Press the Reset button for more than four seconds. (5). Adjust VR2 so that the output is 1.0V. (6). Connect the input to ground and adjust VR3 for 0V output. (7). Re-apply 1.0V to the input and adjust VR2 for 1.0V at the output. Testing The DFA can be extensively tested on the bench. Doing this will also give you good familiarity with the controls and the way in which the DFA works. As is shown in Fig.6, use a temporary pot across the power supply to provide a variable voltage input signal, simulating the output signal of the air-flow meter. Again, one or two multimeters can be used to measure the input and output signals of the DFA. Set the Hand Controller to RUN mode and make sure that as you vary the input signal pot, the load number shown on the display also changes, from a minimum of 1 to a maximum of 128. Note that if you have the DFA calibrated for 0-1V or 0-5V signals, you will be working up at one end of the pot’s rotation. Don’t exceed the maximum input voltage for the calibration range you have picked. Now stop rotating the pot and check that the INPUT load point number stops changing. For example, the display might show: OUTPUT  0 (dV) INPUT 51 /RUN/ Measure the voltage on the DFA output (positive meter probe to the DFA output, negative probe to earth) – for example, the meter might read 2.00V. Now press the   key on the Hand Controller. The OUTPUT number on the LCD should show +1 and the voltage being measured on the multimeter should increase slightly. If this works OK, press the  key further and make sure that the voltage shown on the multimeter rises with each press, then check that the output drops when the  and   keys are pressed. Next, change the INPUT load point by altering the pot voltage and make sure that the output voltage can again be adjusted up and down. Try out the single step , ,  and  white buttons and the 4-step ,  and   black buttons until you ,  become familiar with their operation. Fig.10: this graph shows the changes made to the vane air-flow meter output on a 1985 BMW 735i. In this case, the spring tension within the vane air-flow meter had been tightened a little, leaning mixtures right through the load range. This explains the fact that the Digital Fuel Adjuster was used primarily to enrich the mixtures. This car, which doesn’t use closed loop (ie, has no oxygen sensor) had the mixtures intercepted from idle right through to full load. The DFA was configured in fine resolution mode. 124 PERFORMANCE ELECTRONICS FOR CARS siliconchip.com.au Numbers, Numbers While it may initially seem that a lot of button pushing is needed to construct the tuning map, the actual physical task of punching in even a full 128-point map still only takes five minutes or so. Make sure when entering a large map that you use the “express” black buttons and when you have finished your map, always go back through all load points to make sure that you haven’t inadvertently entered a completely wrong adjustment at any load point. Scrolling through all the load points is easy – just keep your finger constantly on the  or  white button. At the end of a successful tuning session, it is recommended that you jot down the map on a piece of paper – primarily so you can find your way back to the original values if you decide to do some more tuning that turns out not to work so well! VIEW mode can now be tested. Press the RUN/VIEW button to get into VIEW mode and check that up/ down adjustments can be made on the screen at each load point. Note, however, that the multimeter measurement won’t change unless you’re at the load point which is active at that input voltage. Now press the Reset button for more than four seconds, making sure that RESET appears briefly on the screen. That done, measure the input and output voltages, checking that these are identical across the selected range of input voltages. If the outputs are not the same as the inputs (or at least, extremely close), re-check your calibration procedure. LOCK mode is activated by operating the toggle switch on the main unit. Operate this switch and familiarise yourself with its function. It’s a good idea to play with the DFA on the bench until you feel confident as to how it works. You need to know what the displays mean and what each button does. Fitting Fitting the DFA to a car is easy, as there are just four connections. First, ignition-switched +12V is required, siliconchip.com.au This photo shows a prototype of the Digital Fuel Adjuster being tested in a Lexus LS400, using an Autronic air/fuel ratio meter to monitor the changes. In the Lexus, high load mixtures were leaned out. The DFA was also tested in a Subaru Impreza WRX (normal and STi versions), Nissan 200SX, Nissan Maxima V6 Turbo and BMW 735i. along with an earth. That done, the signal to be intercepted (eg, the load signal from the air-flow meter) needs to be cut, with the wire from the sensor going to the input of the DFA and the output from the DFA connecting to the original input to the ECU – see Fig.7(b). These connections should preferably all be made at the ECU. Tuning Warning! The Digital Fuel Ad- juster has immense power over air/fuel ratios. Changing the air/ fuel ratios without using adequate measuring equipment to monitor the real-time air/fuel ratios could result in engine damage! Selecting the wrong air/fuel ratios could result in engine damage! The first step in most tuning processes is to start the car and press the Reset button for about four seconds, returning all the tuning adjustments PERFORMANCE ELECTRONICS FOR CARS 125 Doing The Tuning Yourself The DFA has the power to radically alter mixtures. By the same token, if used carefully it can also be very subtle in the changes it causes – in fine mode, making air/fuel ratio changes as small as 0.1 of a ratio. However, it’s not the sort of device that you fit and just punch in random numbers – taking this approach could cause you to blow your engine after one full-throttle event. As indicated in the main text, the best way of tuning the DFA is with an experienced engine tuner working with your car on the dyno, with the air/fuel ratios being carefully monitored with an accurate, real-time air/fuel ratio meter. Because of the DFA’s simplicity of use, this process should also be fairly quick. However, if you are ultra careful, a lot can also be achieved on the road. First, make enquiries as to whether you can hire or borrow a good air/ fuel ratio meter from a workshop. If you can get hold of such a meter, the complete tuning can be carried out on the road, helped by an assistant. If no such option exists, the Smart Mixture Meter described in Chapter 8 can be used to give you some idea of the mixtures being run. Let’s take a look at the way you’d do it if you’re on a really tight budget and the car you’re working on isn’t worth the price of your house (and isn’t even close!). Say the car uses a turbo engine and you’ve just upgraded the injector size. After the injectors have been installed, the car is idling with the staggers, belching black smoke and running very badly indeed. The DFA has been installed on the air-flow meter output. Here’s the procedure: (1).  Disconnect the oxygen sensor(s) so that no learning can occur. (2).  Using the DFA, reduce the voltage output of the air-flow meter until the car idles smoothly. (3). Reduce the voltage outputs at load points that correspond to gentle driving. (4).  Test drive the car until it drives at Where a supercharger has been added – as with this Lexus V8 – the fuel flow through the standard injectors can be increased by lifting fuel pressure, with fine tuning of the resulting mixtures then able to be carried out with the Digital Fuel Adjuster. to zero. (Remember, the DFA can be configured so that it only intercepts once the car has started, so make sure that when the car is running, LED1 126 PERFORMANCE ELECTRONICS FOR CARS has come on). With the DFA switched in (ie, the LED on) and the map tune reset to zero change, the car should run and drive exactly as it did prior light loads (ie, off boost) smoothly and without hesitation. (5).  Reconnect the oxygen sensor so that self-learning can take place. (6).  Take the car to a dyno to have the high load mixtures set. (The time that needs to be spent on the dyno should have been reduced very substantially – in fact, it might take less than 30 minutes to set up the rest of the map). Alternatively, use the Smart Mixture Meter to set up the air/fuel ratios so that the meter shows full rich under load but the car drives without stutters or black smoke from the exhaust. (7). Check the spark plugs carefully after each full-load run, making sure that they show an appropriate burn. (8).  Listen very carefully for detonation during the whole tuning process (including at light loads). It needs to be stressed as strongly as possible that – especially in high boost turbo engines – it is quite easy to melt an exhaust valve or burn a hole in a piston if the air/fuel ratios are too lean at high loads. to the fitting of the DFA. Any stutters, misses or other poor behaviour should be immediately investigated – don’t try to adjust the mixtures if the car drives differently after having the DFA fitted. If there are problems, recalibrate the DFA for the required voltage range and also go through the test procedure again to make sure that the DFA works correctly on the bench. Also check the integrity of the wiring connections that you have made to the car. For example, make sure that you haven’t reversed the input and output signal connections. (1). Changing Full Load Air/Fuel Ratios: a typical use for the DFA will be to adjust full-load mixtures by modifying the output of the air-flow meter. In RUN mode, the display can be used to work out which load points need to be changed. For example, at low loads (eg, idle), the minimum load point displayed might be 30. In cruising conditions, load points around 50 might be shown, while at wide open throttle at high revs, load points in the 100-120 range siliconchip.com.au Parts List The output of an air-flow meter varies with load. If the high-load air/fuel ratios need to be altered, the DFA can be used to change the output voltage at just these loads – at other loads, the signal remains completely unaltered. might come up on the display. In this case, it’s the latter area where changes will need to be made. In other words, if you have an assistant watching an air/fuel ratio meter and the Hand Controller, it will soon become obvious at which load points changes need to be made. If you have the DFA configured in Coarse mode, don’t change the output voltage in large steps, as the air/fuel ratios might then be dangerously lean. Instead, start off by making small reductions or increases until you get a feel for the sensitivity of the system to changes. As described above, keep the voltage changes at adjoining load points smooth so that there’s no sudden jump in values that could cause an engine stutter. Then it’s simply a case of adjusting the voltage levels up or down at the different load points until the desired air/fuel ratios are achieved. If it is well-tuned, the DFA gives absolutely factory driveability – and tuning is very easy. (2). Overcoming a Turbo Boost Cut: if the car cuts fuel and/or ignition on the basis of the signal received from a MAP sensor or air-flow meter, the DFA can be used to limit the sensor’s output voltage so that the ECU never sees a high enough level to trigger the boost cut. The load point at which the ECU cuts fuel can be read in real time by monitoring the input in RUN mode. The load points above this point can then be reduced just enough so that the cut no longer occurs. Note that depending on the car, the air/fuel ratio may also be changed by this process – it’s wise to check the air/ siliconchip.com.au 1 PC board coded 05car121, 130 x 103mm 1 plastic case, 140 x 111 x 35mm (Jaycar HB 5970) – supplied fully machined with screened panels 1 12V DIL mini relay with DPDT contacts (Jaycar SY-4059) 1 4MHz crystal (X1) 1 SPDT toggle switch (S1) 1 DB25 PC-mount socket 1 18-pin DIL IC socket 2 2-way PC-mount screw terminals 2 2-way pin headers, 2.54mm spacing 2 jumper shunts 4 PC stakes 4 M3 x 6mm screws 1 750mm length of 0.8mm tinned copper wire 1 1m length of red automotive hookup wire 1 1m length of green automotive hook-up wire 1 1m length of black automotive hook-up wire 1 1m length of yellow automotive hook-up wire Semiconductors 2 LM358 dual op amps (IC1,IC2) 1 PIC16F628A-20P microcontroller programmed with voltmod.hex (IC3) 1 TL548, TL549 A/D converter (IC4) 1 DAC0800 D/A converter (IC5) 2 74HC193 4-bit up/down counters (IC6,IC7) 1 7555 CMOS timer (IC8) 1 BT169D SCR (SCR1) 1 5mm red LED (LED1) 1 LM2904CT-5 5V regulator (REG1) 1 7809 9V regulator (REG2) 1 BC337 NPN transistor (Q1) fuel ratios before and after implementing this modification. (3). Changing Injectors: if larger injectors are fitted, the DFA can be used to reduce the output of the airflow meter so that the correct mixtures are retained. In order that the ECU can still stay working roughly within its normal operating envelope, such an injector change shouldn’t be radical, otherwise idle stability will suffer and the car may also not drive very well. Larger injectors will require chang­ ed values at all load points which 1 BC327 PNP transistor (Q2) 1 16V 1W zener diode (ZD1) 4 1N4004 1A diodes (D1,D2,D4,D5) 1 1N4148 diode (D3) Capacitors 1 1000µF 16V PC electrolytic 1 470µF 16V PC electrolytic 3 100µF 16V PC electrolytic 4 10µF 16V PC electrolytic 7 100nF MKT polyester (code 104 or 100n) 1 47nF MKT polyester (code 473 or 47n) 1 10nF MKT polyester (code 103 or 10n) 1 5.6nF MKT polyester (code 562 or 5n6) 1 1nF MKT polyester (code 102 or 1n) 2 22pF ceramic (code 22 or 22p) Potentiometers 1 10kΩ pot (input voltage calibration) 1 10kΩ multi-turn top adjust trimpot (code 502) (VR1) 1 20kΩ multi-turn top adjust trimpot (code 203) (VR2) 1 1kΩ horizontal trimpot (code 102) (VR3) 1 50kΩ multi-turn top adjust trimpot (code 503) (VR4) Resistors (0.25W 1%) 1 1MΩ 1 470kΩ 1 330kΩ 1 100kΩ 1 47kΩ 1 13kΩ 1 12kΩ 8 10kΩ 1 5.6kΩ 1 5.1kΩ 2 3.3kΩ 3 2.2kΩ 1 1.8kΩ 6 1kΩ 1 560Ω 1 330Ω 2 10Ω are accessed and this tuning is best carried out on a dyno with a good air/ fuel ratio meter (see also the “Making Global Tuning Changes” panel). (4). Changing Air-flow Meters: an air-flow meter electrically compatible but slightly larger can be fitted and then the DFA used to recalibrate its output. As with injector swaps, in order that the ECU can still stay working roughly within its normal operating envelope, such a change shouldn’t be radical. Again all load points accessed by the engine are going to require rePERFORMANCE ELECTRONICS FOR CARS 127 Other Car Systems While we’ve concentrated on using the DFA to intercept the output of an air-flow meter, the interceptor is not limited to this function. Any car system that uses a variable voltage output sensor can be intercepted and modified by the DFA. This includes accelerometers (“Gsensors”) used in active 4-wheel drive systems, yaw sensors used in stability control systems, throttle position sensors, etc. Voltage Switch-In? It’s easy to run bigger injectors and then use the Digital Fuel Adjuster to retune the mixtures right through the load range. If you want, you can also change the air-flow meter at the same time! As indicated in the main text, trimpot VR4 can be used to configure the DFA so that it switches in its interception only after the car has started. This function is included because in some cars, the ECU checks the health of the air-flow meter on startup and will register a fault code if the air-flow meter is being intercepted during cranking. Switching in the DFA in after the car has started overcomes this problem. Other cars don’t have any problems with the DFA intercepting signals as soon as power is applied. In these cases, the DFA can be set to operate as soon as the ignition is turned on. Making Global Tuning Changes Any voltage-outputting sensor can be intercepted and tuned with the DFA. That includes air-flow meters, oxygen sensors, MAP sensors and throttle position sensors. mapping and this is best achieved on the dyno (see also the “Making Global Tuning Changes” panel). (5). Changing Oxygen Sensor Signals: the DFA can be configured for the 0-1V signals commonly outputted by oxygen sensors. The resolution remains at 128 load points and the tuning calibration at 127 adjustments up or down, giving extremely fine tuning. The DFA can be used to alter closed loop mixtures (in the same manner as for air-flow meter signal modification), although because of the sudden step in the oxygen sensor output voltage as 128 PERFORMANCE ELECTRONICS FOR CARS mixtures pass through stoichiometric, some experimentation will be needed to get the right results. Conclusion Extensive testing of DFA prototypes on a wide variety of cars showed that it has the ability to provide extremely effective tuning control over air/fuel ratios, together with very easy tuning and simply brilliant drivability. Finally, although not tested in this application, it is almost certain that the DFA can be used to alter the output of G-sensors, allowing tuning It is possible to make a global (ie, overall) shift to the output by adjusting the offset trimpot, VR2. For example, if VR2 is set so that the output is 4V when the input is 5V, then the output will be reduced by 20% for all input voltages. Fine tuning can then be carried out with the Hand Controller. Making a global shift is useful when fitting larger injectors or a larger air-flow meter. of active 4-wheel drive systems and stability control. Acknowledgement Thanks to Lachlan Riddel of ChipTorque for making available his Autronic air/fuel ratio meter during the  development of this project. siliconchip.com.au