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Understanding AFR: Engine Load Compensation

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Engine Load Compensation


00:00 We already know that under high engine load, we are using a portion of the fuel delivered to help control combustion temperature.
00:07 As load increases, or the load is applied for longer, the combustion chamber and piston will become hotter and we may want to increase the fuel delivery further to maintain engine safety.
00:19 Fortunately with modern ECUs we now have a few tricks up our sleeve to help achieve this aim.
00:26 There is no right or wrong way to do this, and the technique will depend on the particular ECU you are using.
00:32 Rather than deal with specifics, I’m going to talk about a few common ways we can do this.
00:38 The important part is to understand what we are trying to achieve, which is to gradually richen the air fuel ratio as the engine is under load for longer periods of time.
00:49 The first way that we can go about this is to use a fuel trim or compensation table based on either gear or road speed.
00:57 It is reasonable to expect that if the car gets to say 6th gear or perhaps 240 km/h, it is being driven under sustained high load.
01:07 At this point in your compensation table, you can simply apply the desired change to your fuelling.
01:14 Another way to achieve this aim is to use a timer function which is common in some ECUs these days.
01:20 The timer function can be configured to work however you want, but in this case you could set it up to start timing when the throttle position exceeds 80%.
01:30 You could then use the input from this timer for a fuel compensation table, and trim in additional fuel once the engine has been at full throttle for perhaps 8 seconds or more.
01:42 Lastly some ECUs have a built in function that calculates average engine load.
01:47 In essence this is a background calculation of engine load vs time and the longer you are at high load or full throttle, the higher the average load value gets.
01:58 You can then compensate your fuel map dependent on the calculated average load.
02:03 If you are using these sort of compensations to target a very rich mixture, then there is a good chance that this will result in a reduction in engine power too.
02:13 It is always preferable to focus on engine reliability over and above outright engine power, but you need to understand how your compensations may effect the engine and power delivery in use.

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