15. Glossary
Terms, acronyms and screen names used in this guide, in the sense in which the guide uses them.
| Term | Definition |
|---|---|
| Absolute pressure | Pressure counted from total vacuum, used in the air calculation. Without a barometer, the VCU arrives at it by adding a fixed 1.01325 bar to the MAP on screen. |
| Acceleration fuel enrichment and decay | Fuel added ahead of time, in % of the base fuel, by the speed of the TPS or the Pedal: positive when the throttle opens, negative (decay) when it closes. It is off by default; with the default settings, any trigger freezes the fast correction and stops the learning. |
| AFR | Ratio between air mass and fuel mass. On the screen, it is just another way of showing lambda: lambda × stoichiometric AFR of the fuel configured in the map. |
| Aggressive cam | High-overlap camshaft. The idle VE can be well below the load VE without being a map error. |
| Apply the learned LTFT | Switch, off by default, that makes the LTFT correct the fuel. Off, the table only observes; leave it that way while collecting. |
| Apply to VE | Button that writes the residual to the VE of the open map and clears the whole learning in the VCU, without confirmation. It does not send the map to the VCU. |
| Authority | How much the correction can move: Fast correction (STFT) limits by MAP for the fast correction and Total authority (STFT + LTFT), 25% by default, for the two together. |
| Bank | Group of injectors (A, B or C) with their own flow rate and rated pressure, on the same VE. What A does not deliver up to the Primary injector opening to bring in the next bank passes to the next one. |
| Base fuel | Fuel that comes out of the VE model, before the enrichments. Acceleration fuel enrichment is given as a % of it. |
| Base map wizard | The Step-by-step map wizard with the Volumetric Efficiency (VE) strategy: generates a VE from scratch, between 30% and 115%, without reading the existing map. It leaves the linearization at zero. |
| BSFC | Brake specific fuel consumption (lb/hp·h). In VE mode it only serves to estimate power and torque in the log. |
| Calibration (of the MAP sensor) | Value added across the whole range of the internal MAP sensor, which changes the air calculation in every cell. It is not a zero button: leave it at 0. |
| Cell | Each point of a table, at an engine speed and a pressure. Near the edge of a cell, the VE used is the blend of the four neighboring cells. |
| Clear LTFT | Button that zeroes values, hits and temperatures of all the cells and copies the axes of the VE that is in the VCU. Use it after sending the new map. |
| Closed loop (Fuel closed loop (VE)) | Fuel correction by the O2 sensor: it compares the O2 sensor with the lambda target and corrects the VE used by a factor, without changing the table. It is off in a new map. |
| Closed Loop / VE Probe | The lambda that the loop reads: average of the sensors marked in Sensor selection for average value, with valid readings from 0.2 up. |
| Commit (Commit to VE) | Page that takes the residual to the VE of the open map: new VE = current VE × (1 + residual × Percentage to apply), 50% by default. The Preview shows beforehand what changes. |
| Conditions (gates) | List on the VE learning (LTFT) screen: green is free, red freezes or zeroes the correction, yellow only blocks the learning. |
| Dead band | Error below which the loop does not correct, so as not to chase the noise of the O2 sensor: 0.7% by default (0.007 in Lambda error dead band). |
| Deadtime | Delay for the injector to open and close. In VE mode, the full value from the table is added to each pulse, according to the battery voltage and the differential pressure. |
| Deadtime fraction | Part of the pulse that is deadtime: Primary injectors deadtime ÷ Injection time A. Above 35%, as a starting point, do not correct the VE by the O2 sensor. |
| Diagnostic | Page that checks whether the learned error really is the VE's, with four tests: global error, deadtime, charge temperature and error only at idle. |
| Differential pressure | Fuel pressure in the line minus the pressure in the manifold. The flow rate of the injector grows with its square root; it corrects the useful time and chooses the deadtime row. |
| Direct injection (DI) | Injector in the cylinder, fed by a high-pressure rail. In VE, the rail pressure enters through the Differential fuel pressure deviation compensation, in the DI Fuel pressure 1 or DI 2 mode. |
| Displacement | Total volume of the engine, entered in Engine volume (cc, CI or L). The calculation uses the volume of one cylinder: displacement ÷ Number of cylinders. |
| Effective VE | VE used in the calculation: table VE × VE factor. In the log: VE - Effective efficiency %. |
| Engine temperature compensation | The warm-up: percentage on the useful time by engine temperature, the same table as in pulsewidth mode. With the loop on, zero it from the minimum temperature of the loop up. |
| Enrichment | Percentage added to the useful time: warm-up, post-start, acceleration fuel enrichment, gear and external actions. The percentages add up, they are not multiplied, and they do not move the lambda target. |
| Exhaust transport constant | Part of the delay that says where the O2 sensor is, divided by the fuel flow rate. Default 0.020 s·l/min; increase it for an O2 sensor far from the manifold. |
| Failsafe | Value that the VCU uses in place of a sensor when the Use ... sensor switch is off or the sensor is in failure. |
| Flex fuel | Function that, with the ethanol sensor, makes the VCU use the stoichiometric AFR of the measured mixture, between pure gasoline (14.7) and anhydrous ethanol (9.0). With it active, work in lambda. |
| Flex IO | FT470 pin that works as an input or as an output, never both. There are 20: 8 blue (injection outputs), 8 gray (ignition) and 4 yellow. |
| Flow rate of each primary injector | Flow rate of one injector, not of the bank, at the rated pressure. The VCU uses the flow rate in mass; in cc/min, FuelTech Vision converts it by the density of the chosen fuel. |
| Freeze | The correction stops correcting and keeps only the integral part. If the engine moves one cell, it slides to the value of the new point, with a time constant of 1 s. |
| Fuel cut | Injection cut, cut on deceleration (Deceleration fuel cut-off) or on a gear change. It freezes the correction, which comes back at least 2.0 s after the end of the cut. |
| Fuel strategy | Field of Engine settings: Injector Pulsewidth (table in ms) or VE Based (table in VE; the VCU calculates the ms). Switching does not convert the map. |
| FuelTech Vision | Computer program in which you edit the map and write it to the VCU; it also opens the log and the learning screen. |
| Gauge pressure | Pressure relative to the atmosphere: negative is vacuum, positive is boost pressure. It is how the MAP appears on the screen and on the axes of the VE tables, including in kPa. |
| Grid | Set of points of the axes of a table. Recommended: up to 16 × 16 on the VE, because of the learning, and 10 × 10 on the target, with axes of equal step. |
| Heel and toe | Quick throttle blip when downshifting, to match the engine speed. With an electronic throttle commanded by the VCU, the Pedal source of acceleration fuel enrichment does not see it. |
| Hit | One transfer counted in a cell. It measures the confidence of the cell: it counts transfers, not passes of the engine through it. |
| IAT and PW | Acronyms on the Diagnostic page: IAT is the intake air temperature; PW is the injection time. |
| Ideal gas law | Relation that gives how much air fits in a cylinder: absolute pressure × volume ÷ (air constant × temperature in kelvin). The air constant is 0.0028705 bar·L/(g·K). |
| Injection mode for engine start bank A | Engine start fuel injection table: the cranking uses the Engine start table, in ms. Fuel injection main table: the cranking comes from the VE model, with warm-up, post-start and deadtime. |
| Injector | Valve that injects the fuel. The VCU commands how long it stays open. |
| Injector duty cycle (opening) | Fraction of the cycle in which the injector stays open, in the Injection duty A channel. With a bank at 100%, the loop freezes. |
| Injectors saturated (staging) | Condition in the Conditions (gates) list: injector at 100% of the cycle in some bank, not the passage from one bank to another. It freezes the correction. |
| Intake manifold | Duct that carries the air to the intake valves. The pressure and the temperature of the air in it enter the air calculation. |
| Integral part | Part of the correction that accumulates the error and carries the correction that stays. By default, the integral time is 3 times the estimated delay (Integral time constant (x delay)). |
| Interpolation | Value between the points of the table, in a straight line, from the four neighboring cells. Outside the table there is no extrapolation: the VCU repeats the edge value. |
| Inverse calculation | Conversion of the pulsewidth map to VE, cell by cell: finding the VE that gives the same fuel that the pulse of the pulsewidth map gave. |
| Lambda | Measure of the mixture relative to the stoichiometric one: 1 is stoichiometric, below 1 is rich, above 1 is lean. The VCU always stores and uses the target in lambda. |
| Lambda error (O2 sensor vs target) | Channel with the relative difference between the O2 sensor and the target of the same instant, in %. Positive means a mixture leaner than the target. |
| Lambda target table by MAP | Table of the lambda you ask for at each engine speed and manifold pressure, with its own axes. The enrichments do not shift this target; only flex shifts it. |
| Launch, anti-lag (ALS) and pit limit | Launch: 2-step, 3-step and burnout. Anti-lag: keeps the turbo pressure with the throttle closed. Pit limit: limits the speed in the pits. In VE mode, while they act, the loop freezes (state Launch / ALS / pit limit). |
| Linearization | Correction in ms for short pulses, in which the injector does not deliver fuel in proportion to the time. Table per bank, with one row per cylinder (Primary injector linearization), which starts at zero. |
| LTFT | Long-term fuel trim, the Long term learning (LTFT): table of up to 16 × 16 in the VCU memory, outside the map, that stores per cell the stable part of the fast correction. |
| Main MAP VE table | The VE table: filling of the engine in %, from 0 to 300%, by engine speed and MAP, up to 32 × 32. A single one for the whole engine. |
| Manifold-referenced regulator | Fuel pressure regulator that follows the MAP and keeps the differential pressure almost constant. Without a pressure sensor, the calculation is only right with it; a line with fixed pressure needs the sensor. |
| MAP | Pressure in the intake manifold and the sensor that measures it. On the screen it appears as gauge pressure; it is the load axis of the VE tables. |
| MAP estimated by TPS | Table of the expected manifold pressure, in gauge bar, by engine speed and throttle position. The factory default never goes above 0 bar: it is for a naturally aspirated engine. |
| MAP failsafe | Chooses what replaces the MAP with Use MAP sensor off or with the external sensor in failure: MAP estimated by TPS table (default) or Fixed value. |
| Minimum confidence (hits) | Hits that the cell needs to have to enter the Diagnostic, the Preview and the Commit: 20 by default, from 1 to 200. |
| Only enrich above the set pressure | Switch, off by default, that above the set pressure (0.30 bar gauge by default) zeroes the lower limit of the fast correction: it can only add fuel. |
| Overlay | Feature of the log chart (Overlay button) that marks on the VE table the engine speed and the MAP of the instant of the cursor. |
| Post start enrichment | The post-start: percentage by engine temperature and time since the start, up to the last time of the table (8 s by default). During it, the loop stays paused. |
| Primary injector rated pressure | Pressure at which the rated flow rate holds; the two form a pair. Enter the pair at the working differential pressure: the rated pressure is also the center of the learning window. |
| Primary injectors deadtime | Deadtime table, 8 × 8, in ms: battery voltage in the columns and differential pressure in the rows. The value used appears in the Primary injectors deadtime channel. |
| Primary mode | Multipoint, Semi-sequential (default) or Sequential. In Multipoint, on a piston engine, the bank fires twice per cycle: half of the useful time and the full deadtime in each pulse. |
| Pro-Nitrous | Nitrous function of the VCU that adds fuel in milliseconds per bank and per cylinder. In VE mode this fuel is not applied and the mixture goes lean when the nitrous is activated. |
| Pulse (pulse width) | Total injector command time: useful time × (1 + enrichments + cylinder trim), plus linearization and deadtime. |
| Reference deadtime | Deadtime built into the pulse of the table in pulsewidth mode (Reference deadtime for primaries injectors). It does not exist in VE mode; subtract it in the inverse calculation. |
| Required VE | VE that would make the model match the engine at that instant: effective VE × O2 sensor ÷ target × (1 + enrichment ÷ 100). Build it as a calculated channel in the log viewer. |
| Residual | LTFT minus the components that the Diagnostic explained, with Remove the explained components from the residual on. It is what the Commit takes to the VE. |
| Slot seq | Counter at the bottom of the VE learning (LTFT) screen that goes up each time the learning is saved in the VCU memory. |
| Speed-density | Name of the calculation by VE: the fuel comes from the air mass calculated from the manifold pressure and temperature and from the displacement. |
| Steady state | Steady pedal and MAP, within the transient limits (5% TPS and 0.05 bar MAP, by default); the RPM may rise, as in a full-throttle pull. Only at steady state does the loop correct and learn, and only a steady-state segment, after the O2 sensor delay, serves to read the VE in the log. |
| Steady-state enrichment | Percentage that stays on with the warm engine at steady state, such as warm-up above the minimum temperature of the loop or gear. The loop treats it as an error and the learning may record it. |
| STFT | Short-term fuel trim, the Fast correction (STFT) of the loop: it corrects the O2 sensor error right now, a single value for the engine point, and goes to zero with the engine stopped. In the log: VE closed loop - STFT. |
| STFT saturated (VE probably wrong) | State with the fast correction at the limit for more than 30 s: the error is bigger than the limit and the learning stops. Correct the region by hand, from the log. |
| Stoichiometric AFR | AFR of the chemically correct mixture of the fuel in use; it divides the air mass in the calculation. It comes from the Fuel: 12.6 in Regular BR Gasoline (E27) (Brazil) and 8.4 in Ethanol (pump) (Brazilian hydrous ethanol). |
| TPS | Throttle position, in %, and the sensor that measures it. It is the axis of the MAP estimated by TPS table and one of the sources of acceleration fuel enrichment. |
| Transfer | Passing a fraction of the fast correction to the LTFT, when it stays at 1.5% or more for 4 s in a row in the same active cell, the closest one to the engine point. |
| Transient | Quick change of load: TPS varying more than 5% or MAP more than 0.05 bar, at the defaults. It freezes the fast correction and blocks the learning. |
| Transport delay | Time between the injector injecting and the O2 sensor seeing the result. The VCU estimates it and compares the O2 sensor with the target delayed by that time; the value is in VE closed loop - Estimated delay. |
| Trigger wheel | Toothed wheel whose sensor reports the engine speed to the VCU. The fuel calculation is redone on every revolution of it. |
| Use ... sensor | Switches on the Sensors and failsafe tab: on, the calculation reads the sensor; off, it uses the failsafe. They are on by default: without an air temperature or fuel pressure sensor, turn off the switch for it. |
| Useful time | Time in which the injector actually injects, with the deadtime already subtracted (also called effective pulse width). In the log, with the enrichments already included: Injection time A minus Primary injectors deadtime. |
| VCU | The electronic control unit that runs the map and commands the injection: FT700 or FT470 in this guide. |
| VE closed loop - State | Channel with the number of the loop state; the VE learning (LTFT) screen shows the same state in text. Only the one with the highest priority appears. |
| VE factor | Total correction that multiplies the VE of the table: (1 + applied LTFT) × (1 + STFT). 1.000 is no correction; by default, it stays between 0.75 and 1.25 (VE closed loop - VE factor). |
| VE learning (LTFT) | Learning screen, with the Live, Diagnostic and Commit to VE pages. It only works with the VCU connected; on the computer, it is in the Tools menu. |
| Volumetric efficiency (VE) | Ratio between the air that enters the cylinder on each cycle and what would fit in its displacement, at the absolute pressure and the temperature of the manifold. It measures only the filling; it is not a load index. |
| Wideband O2 sensor | Sensor in the exhaust that measures the lambda of the burned mixture. Each sensor needs a conditioner, the circuit that reads it: the FT700 has 2 internal ones and the FT470 has 1; the other sensors come in through an analog input or CAN. |