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Tuning for new injectors

There are two primary maps that need to be modified when replacing fuel injectors. Injector scaling and injector dead time. To understand how these values interact, here is the basic formula to determine fuel injector pulse width:

((fuel table value + 1) * mass air flow * injector scaling * k) + injector dead time = final injector pulse width

Or in English: The current mass air flow is enriched over stoic by the fuel table value, then multiplied against the injector scaling constant, then finally the dead time is added to the product to produce the total injector pulse width. Note that the fuel table in almost all editing solutions is displayed as target AFR, however the actual ECU value is an enrichment (example: for Subaru Denso DBW ECU, value 0 is 14.7:1, 0.50 is 9.8:1, etc).

k represents unknown constants to allow for unit of measure concerns.

Injector scaling is stored in the ECU as an on time value constant. This is inverse to referring to the value as mass flow over time, which is typically advertised. That is, while a larger injector is quoted with a larger value number, the ECU will actually want a lower value to compensate since the injector will need to be opened for a shorter period of time under the same circumstances.

It is possible to modify the XML definition to display the ECU value inversely to approximate the typical "cc/min" or "lbs./min" values of injectors. Injector value needs to be tuned in the actual car accurately regardless of how the XML is written. It is only important to keep in mind what unit of measure is being used to avoid confusion.

Suggested steps for tuning

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