Ethanol & Flex Fuel Tuning: Tuning Process
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Tuning Process
07.30
For a refresher on injector scaling please refer back to the Practical Reflash Tuning course.
| 00:00 | - As we've just discussed, many of the OE ECUs we'll deal with don't allow the tuner to directly adjust the fuel properties. |
| 00:07 | This is occasionally dealt with incorrectly by tuners by adjusting the mass air flow sensor scaling. |
| 00:13 | Doing this tells the ECU that more air is entering the engine and hence more fuel will be delivered by the injectors. |
| 00:21 | The problem is that this also affects all of the ECUs calculations that are based around mass air flow. |
| 00:27 | For example the load point that we'll be using in the ignition table won't be accurate, and if the ECU is calculating torque based off the engine's air flow, then this calculation will also be wrong. |
| 00:39 | Particularly when you consider that we need to change the fuel volume by around 40% to cope with E85 it's easy to understand that adjusting the MAF scaling can have some big implications. |
| 00:51 | The other issue you may strike is that you may end up reaching the limit of the MAF scaling before you achieve a scaling that will actually achieve your desired air fuel ratio. |
| 01:01 | Instead of adjusting the MAF scaling, the correct technique is to adjust the injector scaling data instead, to essentially tell the ECU that the injectors fitted to it are smaller than they really are. |
| 01:14 | This has the effect of the ECU increasing the pulse width being sent to the injectors and hence more fuel will be delivered. |
| 01:22 | This means that we can leave the MAF scaling unaltered, and the ECU still has an accurate MAF input to base its calculations off. |
| 01:30 | Rescaling the injectors however does require that the current MAF calibration that we're using is accurate. |
| 01:37 | If the MAF scaling is inaccurate, as is often the case when we fit a modified intake or pod filter, this will make it impossible to accurately tune the ECU, since if there's an error between our target air fuel ratio and measured air fuel ratio, this could be the result of an incorrect MAF calibration or injector scaling and there's no way to know which is causing the issue. |
| 02:00 | Now that we understand what we're trying to achieve let's look at the tuning process. |
| 02:05 | In this case I've broken the process down into five individual steps. |
| 02:10 | The first step is to ensure that our calibration is accurate for gasoline. |
| 02:15 | It's quite common for example for tuners to upgrade the injectors when intending to develop an ethanol tune. |
| 02:22 | And we want to make sure that prior to this happening, the MAF calibration is accurate. |
| 02:27 | Even relatively minor changes to the intake system can affect the accuracy of the MAF calibration and we need to account for these before we fit larger injectors or it's going to be impossible to know where the error's coming from. |
| 02:42 | The process here is to use the short term and long term fuel trims or alternatively to look at the error between the commanded air fuel ratio and the measured air fuel ratio. |
| 02:52 | If the MAF scaling is accurate, then the closed loop trims should be very close to zero, or alternatively our measured air fuel ratio should track our commanded air fuel ratio. |
| 03:03 | In practice it's not possible to have our closed loop trims constantly sitting at zero, and generally provided we can achieve trims in the region of approximately 5% or better we can move on. |
| 03:15 | Once we have the MAF scaling correct we can then fit our larger injectors if desired and go through the process of adjusting the injector scaling and latency to get our fuel trims back on track. |
| 03:27 | This process is all detailed thoroughly in or Practical Reflash Tuning course if you need a more detailed description of the process. |
| 03:36 | Once the calibration is correct for gasoline we can then save the file with an appropriate name, so that we can easily locate it at a later point when we want to go back to a gasoline tune. |
| 03:47 | For simplicity I usually add the term pump gas or similar to the file name. |
| 03:52 | I'll then straight away save the file again with the term ethanol or similar. |
| 03:58 | This ensures that when we get to the following steps, we will be modifying the correct ethanol file. |
| 04:04 | With our base calibration complete, the second step is to drain the fuel system and refill it with our secondary fuel. |
| 04:11 | During this step we want to be careful about contamination of the fuel system from any of the primary fuel that may remain in the tank and fuel lines. |
| 04:20 | You can refer back to the swapping fuels module for a refresher on the techniques and precautions I recommend. |
| 04:27 | The third step is to make a change to our injector scaling in order to be able to get the engine up and running on ethanol so that we can start logging some data in order to fine tune the calibration. |
| 04:39 | Remember here that we need to reduce the injector scaling values so that the ECU thinks the injector is smaller. |
| 04:46 | This will mean the injector pulse width will be increased for a given mass air flow. |
| 04:52 | A good place to start is by taking into account the required increase in fuel volume for the ethanol content that we're tuning for. |
| 05:00 | For example as we know already, E85 will require approximately 40% more fuel volume when compared with gasoline. |
| 05:08 | We can then use this data to help us choose a suitable injector scaling value. |
| 05:14 | What we want to do here is divide the gasoline injector scaling value by our ethanol multiplier. |
| 05:21 | If you're using E85 then the multiplier is 1.4 If we had a gasoline injector scaling value of 1000cc per minute for example, then we'd divide this by 1.4 which would give us a new injector scaling value of 714cc per minute. |
| 05:39 | This is unlikely to be perfect but it should be sufficient to get you up and running so that you can begin the tuning process. |
| 05:47 | To make things simple you'll find an Excel spreadsheet attached to this module, where you can simply enter your gasoline injector scaling and ethanol content and the spreadsheet will tell you what the new scaling value should be. |
| 06:01 | Before we move on, we also want to increase the cranking fuel delivery to get the engine starting well on ethanol. |
| 06:08 | The fourth step is to get the engine running and then optimise the injector scaling until our close loop trims as as close to zero as we can achieve or there's minimal error between our commanded air fuel ratio and our measured air fuel ratio. |
| 06:22 | We want to remember while we're doing this, that the ECU will still be scaled for a stoichiometric air fuel ratio of 14.7:1 to suit gasoline so the target air fuel ratio numbers we'll see in the fuel tables will not represent true air fuel ratio on our ethanol blend. |
| 06:40 | With the fuel delivery under control, the fifth and final step of the process, is to complete a full comprehensive tune on our ethanol fuel blend. |
| 06:49 | This includes optimising the fuel table, ignition table, boost control, and cold start settings. |
| 06:56 | So let's just quickly recap those steps. |
| 07:00 | We want to start by making sure the MAF calibration and injector scaling are good and accurate for gasoline. |
| 07:06 | Following this we can drain and refill the tank with our ethanol fuel blend. |
| 07:11 | Next we can make a change to our injector scaling to account for the ethanol blend that we're running. |
| 07:16 | Now we can get the engine running on the ethanol blend, and optimise the injector scaling correctly. |
| 07:22 | Lastly we can perform a comprehensive tune to suit the ethanol fuel. |
