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Fuel Settings

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.

Fuel Adjustments Table

The Fuel Adjustments Table 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.

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:

Real adj = -5% * (1.0 - 0.8) / (1.6 - 0.8) = -1.25%

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.

Settings

The Global fuel and Deadtime 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. There is also a secondary fuel scale and deadtime adjustment conditionally applied with Full V3 (see the ECU Config→AuxMaps tab). But you have to go out of your way to enable that, so it's not something we'll cover here.

Global fuel

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 Global fuel adjustment value to, say, -50% to compensate for 900 cc/min injectors cuts fuel delivery in half.

The needed Global fuel adjustment value may be calculated as follows:

FlowRateAdj1G = squareroot(BaseFuelPressure / 37)
FlowRateAdj2G = squareroot(BaseFuelPressure / 42.6)
FlowRateAdjEVO1-3 = squareroot(BaseFuelPressure / 42.6)
NewInjFlow = InjectorCCPerMin * FlowRateAdj
Adj = (100 * ( 450 / NewInjFlow ) ) - 100

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.

Deadtime

ECMLink provides access to the factory deadtime adjustment table in the DirectAccess tab. The line item is called “InjBatteryAdj”. This is a table of injector offsets to apply based on battery voltage. The global deadtime field on the ECU Config→Fuel tab is simply added to whatever value is derived from that InjBatteryAdj field. Typically, the larger the injector or the higher the fuel pressure, the greater the injector's deadtime.

The Deadtime adjustment value usually needs some tweaking to get actual air/fuel ratios to match what the ECU intends. Since the Deadtime adjustment value is added to the injector pulsewidth, altering it tends to change the actual air/fuel ratio mostly at idle where the base injector pulsewidth is small and the deadtime adjustment is relatively large. Deadtime adjustment has very little effect at wide open throttle where injector pulsewidth is already considerably larger.

fuelsettingshelp.txt · Last modified: 2014/10/27 07:19 by twdorris