ECMTuning - wiki

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<h1>Fuel Settings</h1> <div class="level1"> <p> This page describes the basic usage of the Fuel tab in the ECU Config section of the ECMLink application. This page is just a dump and reformat of the same information provided in the help file with the ECMLink application. </p> </div> <h2>Fuel Adjustments Table</h2> <div class="level2"> <p> The <b>Fuel Adjustments Table</b> allows rpm-based adjustment of the air fuel ratio relative to the ECU's stock operation.  Moving a point up (or increasing the adjustment value by typing in the numeric table) makes the mixture richer; lowering it makes the mixture leaner.  An adjustment of, say, -5% means multiplying the stock fuel amount by 0.95 (delivering 5% less fuel than stock).  Most adjustments will be negative numbers since stock fuel delivery is a rather rich, conservative mixture.  Between rpm points, the ECU interpolates between the two adjacent rpm settings. </p> <p> The adjustment described in the preceeding pargraph is fully applied only when the value for LoadFactor (essentially the same as Airflow/rev [or Boost adjusted by VE]) is above 1.6 (about 10 psi of boost).  Below a LoadFactor of 0.8 (roughly atmospheric pressure) none of the adjustment is applied.  Between a LoadFactor of 0.8 and 1.6, the adjustment is applied proportionally.  For example, a -5% adjustment value at a LoadFactor of 1.0 results in a -1.25% adjustment actually applied: </p> <pre class="code">Real adj = -5% * (1.0 - 0.8) / (1.6 - 0.8) = -1.25% </pre><p> </p> <p> Multiple contiguous fuel adjustment points may be selected by holding the Shift key and using the mouse or the left/right arrow keys, and adjusted simultaneously in equal increments using the up/down arrow keys or dragging with the mouse up/down. </p> </div> <h2>Settings</h2> <div class="level2"> <p> The <b>Global fuel</b> and <b>Deadtime</b> adjustments are intended to be used mainly to compensate for injector flow rate and fuel pressure that differ from stock. They are applied at all times. </p> </div> <h3>Global fuel</h3> <div class="level3"> <p> The stock ECU assumes that the car is equipped with 450 cc/min injectors and a fuel pressure of either 37 psi (1G) or 42.6 psi (2G).  As injector size is increased, the Global fuel adjustment must be made more negative.  Reducing the <b>Global fuel</b> adjustment value to, say, -50% to compensate for 900 cc/min injectors cuts fuel delivery in half. </p> <p> The needed Global fuel adjustment value may be calculated as follows: </p> <pre class="code">FlowRateAdj1G = squareroot(BaseFuelPressure / 37) FlowRateAdj2G = squareroot(BaseFuelPressure / 42.6) FlowRateAdjEVO1-3 = squareroot(BaseFuelPressure / 42.6) NewInjFlow = InjectorCCPerMin * FlowRateAdj Adj = (100 * ( 450 / NewInjFlow ) ) - 100 </pre><p> </p> <p> Where BaseFuelPressure is specified in PSI and InjectorCCPerMin is the flowrate of the injectors at 43.5psi (the standard flowrate reference pressure).  Some slight empirical tweaking of this theoretically-derived value may be needed to get actual air/fuel ratios to match what the ECU intends.  Since the Global fuel adjustment value is a multiplier applied to the injector pulsewidth, altering it tends to change the actual air/fuel ratio proportionally under all conditions. </p> </div> <h3>Deadtime</h3> <div class="level3"> <p> The ECU assumes a nominal 700 microseconds of injector deadtime (for stock injectors).  The Deadtime adjustment value is the number of microseconds added to that to compensate for injectors that react more slowly than stock injectors.  Typically, the larger the injector or the higher the fuel pressure, the greater the injector's deadtime. </p> <p> The <b>Deadtime</b> adjustment value usually needs some tweaking to get actual air/fuel ratios to match what the ECU intends.  Since the <b>Deadtime</b> adjustment value is added to the injector pulsewidth, altering it tends to change the actual air/fuel ratio mostly at idle and very little at wide-open throttle. </p> </div>