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Practical Reflash Tuning: Step 4: MAF/Injector Scaling

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Step 4: MAF/Injector Scaling

04.03

00:01 - The fourth step of our conventional reflashing process is where we will be recalibrating or rescaling our mass air flow sensor, and adjusting our calibration to suit a different set of injectors.
00:12 Now as I mentioned at the start of this worked example, in some ways the Hondata doesn't fit into a conventional reflash strategy, and particularly because it is a speed density based ECU, we have no mass air flow sensor to adjust or rescale.
00:29 So there's not a lot of work for us to do in this step.
00:32 If we have fitted a different set of injectors though then we will need to make some adjustments.
00:38 So let's jump into our K Manager software, and we'll have a look at what we would need to do here.
00:43 So we're on the fuel injectors tab here, and the process is pretty straightforward, there's not a lot of work for us to do.
00:50 First of all we're going to start by entering the flow rate of our new injectors.
00:55 So this is the flow rate of the injectors at whatever pressure we've chosen to run them at, and this will come from our manufacturer's data.
01:03 We also need to enter the injector voltage compensation values.
01:08 This is also often referred to as battery compensation, injector latency, injector dead time, or injector offset.
01:16 Again this data will come from your injector supplier.
01:20 If you are running one of the small set of injectors that are predefined, you can click on the injector voltage comp quick select button here, and choose from one of these predefined injectors.
01:32 Now there are a couple of caveats that we need to understand here with the way the Honda ECU deals with injector scaling or injector size.
01:40 First of all if we've got an existing tune where the fuel tables have all been adjusted and tuned correctly to achieve our target air fuel ratios, and we are now going to fit a larger set of injectors, if we want any hope of our air fuel ratio still tracking our targets when we fit those new injectors, it is essential that the initial tune was completed with the correct injector size in this particular tab.
02:09 What I mean here is that if this particular value here for our injector size was left at the factory value of 310cc, but for whatever reason we actually had a set of 440cc injectors fitted to the engine, it's still possible to get our engine running correctly and on target.
02:29 What we're simply going to be doing there is manipulating all of our fuel tables in order to get the correct pulse width out of the injector.
02:36 That's all well and good but then when it comes time to upgrade to a larger set of injectors where we have known data, if we now enter the correct data for those injectors, the ECU is not going to be able to apply the correct background compensation and we're going to find that our fuelling will be off.
02:54 So that's one small trap, if you're dealing with a Hondata ECU that's previously been tuned by a tuner who didn't understand the correct procedure.
03:03 The other aspect here that we need to understand is that the injector characterisation data that the Honda ECU uses is relatively simplistic.
03:12 We're only looking here at a rate of flow value and also the injector dead time or offset data.
03:21 Now this doesn't take into account non linear areas of flow.
03:25 And what this means is that even when we are entering the correct data for our injectors, it's likely that this will get us in the ballpark and our fuelling should be relatively close to our existing targets.
03:37 But we're inevitably still going to see some errors creep in.
03:41 So I like to think of this as a coarse adjustment to get our fuelling back in the ballpark.
03:46 We're still going to need to go through our fuel tables and make more refined smaller adjustments to correct any remaining error.