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Practical Reflash Tuning: Compensations

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Compensations

03.49

00:00 - One of the advantages with modern EFI is it's ability to maintain a consistent tune as atmospheric conditions change.
00:09 Some of this ability is due to the compensation tables included inside the ECU that allow aspects of the fuel or ignition to be altered as required, and in this module, we're going to discuss these compensations in detail.
00:25 One of the key considerations in maintaining a consistent air fuel ratio as atmospheric conditions change is altering the fuel delivery as the air density changes.
00:38 Air density in particular is affected by air pressure which varies with altitude as well as air temperature.
00:46 Higher altitude and hotter air temperatures result in lower air density which means that the air contains less oxygen.
00:56 In turn, this means that we need to supply less fuel in order to achieve the same air fuel ratio.
01:04 If the ECU uses a MAF sensor as the load input, then remember that the MAF is directly measuring air mass, and hence air density is accounted for before the signal reaches the ECU.
01:19 This means that theoretically, the ECU can maintain a consistent air fuel ratio as air density varies.
01:27 In a MAP based system, air temperature is measured and accounted for in the ECUs fuel calculation as air temperature is one of the components of the ideal gas law which is how the ECU calculates mass air flow.
01:44 With this in mind, it's understandable that most OE ECUs won't offer a separate air temperature compensation table for fuel delivery as it's assumed this is dealt with by the ECUs fuel calculation.
02:00 We may however have compensations available for aspects such as ignition advance or boost target to help ensure engine safety if operating conditions become adverse.
02:14 For the same reason, the ECU may include compensation tables based on engine coolant temperature that can be useful to aid cold start performance as well as offering protection at extreme engine temperatures.
02:29 While we're discussing cold start performance, you might also find compensation tables for cranking enrichment or post start enrichment in some ECUs.
02:40 One aspect to watch out for is that some of these compensation tables may be defined in units of injector pulse width whereas in the after market ECU world, it would be more typical for any cranking or post start compensations to be expressed as a multiplier on the main fuel delivery.
03:01 This isn't an issue when you're running stock injectors, but if you fit larger injectors, you'll need to visit these compensation tables and make appropriate adjustments to the injector pulse width or the ECU will adding too much fuel in these situations.
03:19 One of the advantages of refleshing a stock ECU is that in many instances, we won't need to touch any of the compensation tables particularly if the modifications you're adjusting the tune for are only slight.