Road Tuning: Fuel Table Configuration
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Fuel Table Configuration
06.45
| 00:00 | Before we actually configure the fuel table, you need to decide what parameter you want to use for the load axis on the table. |
| 00:08 | If you change this later on, it will affect your entire tune, so you want to get this right first. |
| 00:14 | The correct option is going to depend on your engine configuration, but 90% of engines are going to use manifold pressure. |
| 00:21 | Manifold pressure is an essential element of the speed density principle, so it makes sense that the ECU wants to see this value to calculate airflow through the engine. |
| 00:32 | While it isn't a popular choice for an aftermarket standalone ECU, it is possible with some ECUs to use a mass airflow sensor. |
| 00:40 | There are very few instances where you would want to do this, unless the rules for a particular class Dictate that removing the MAF and adding a MAP sensor are not legal. |
| 00:50 | The other option that is occasionally used for the engine load is throttle position. |
| 00:55 | This is also known as alpha N. |
| 00:58 | You would only consider using throttle position in an engine that runs multi-throttle bodies where the engine vacuum is no longer a good reference for engine load. |
| 01:07 | It can also be used in heavily cammed engines which produce very little vacuum at idle. |
| 01:13 | If you're running an engine that uses both multi-throttle bodies and forced induction, you'll need to use a more complicated model for fuel that incorporates both throttle position and manifold pressure. |
| 01:25 | This is an advanced topic that's beyond the scope of this course though, and this is something that should only be attempted by experienced tuners. |
| 01:34 | In our example, we're going to be using manifold pressure for the load axis, but we also need to choose an appropriate range for both the load and rpm. |
| 01:44 | Your ECU will have a menu that allows the axes of the tables to be changed, and we just need to go to this to start with. |
| 01:51 | If I'm not familiar with an engine, I'll start by adding rpm zones every 500 from zero through to 500 beyond the expected rev limit. |
| 02:01 | It can also be useful to add an extra zone in around your desired idle speed to improve accuracy of tuning at this point. |
| 02:09 | If we're using a manifold pressure sensor for the load axis, I'll start with load points every 20 kPa and then add another couple of load points around the idle and cruise areas of the map. |
| 02:21 | The actual manifold pressure of the engine we used for idle and cruise will depend on the engine and cam overlap, so you will need to test and adjust this. |
| 02:29 | I would start by adding zones at 30 and 50 kPa. |
| 02:33 | If you're using throttle position, the load points are a little different. |
| 02:38 | The airflow through a throttle body is very non-linear. |
| 02:41 | This means that you get a large increase in airflow over the first 50% of throttle travel, and much less of an increase over the remainder. |
| 02:50 | To be able to get really good fuel control and smooth drivability just off idle, I would usually use zones at zero, 2.5, 5%, 10%, 15% and 20%. |
| 03:03 | This gives very fine resolution down near closed throttle where we need it. |
| 03:07 | Above 20%, you can add zones every 10%, to give 30, 40, 50 and 60%. |
| 03:15 | At this point, we can expand the resolution even further and add zones at 80 and 100%. |
| 03:21 | You'll most likely find that when it comes time to tune, that the fuel numbers between the 80 and 100% columns are almost identical. |
| 03:29 | Now that we have our axes set up, the next job is to enter some numbers into the map that will get the engine running. |
| 03:36 | This is the part that novice tuners get worried about assuming they need the perfect number in the map to get the engine running without the risk of damage. |
| 03:45 | As you will see in the initial startup module, this really isn't overly critical, and we're going to see what to do to get these numbers dialled in really quickly after startup. |
| 03:56 | We still want a reasonable starting point in these tables, and if you wanted to spend the time, it is possible to go through the calculations we looked at in the EFI Fundamentals course and develop a pretty good startup map that will be close. |
| 04:11 | Unless you actually know the engine's volumetric efficiency though, there is still some guesswork involved, so my preference is to save the time and put some basic numbers in the map, which will be close enough to get us up and running. |
| 04:24 | We can worry about fine tuning later. |
| 04:28 | If we have a VE-based fuel map, you can expect most engines to idle with a VE of around 40-60%. |
| 04:35 | We also know that around peak torque, we can expect to see VE hit somewhere around 90-100% depending on the engine design, but without getting too fussy, we can simply enter a VE of 50% across the entire map for now. |
| 04:52 | For a millisecond-based fuel map, choosing numbers for the fuel map is a little more involved, since the numbers in the main fuel map are going to depend on the size of the fuel injector, the base injector pulse width, and the VE of the engine. |
| 05:06 | It might sound like a lot to take in, but we aren't going to get too tied up on this. |
| 05:11 | We'll be able to sort out the specific tuning once we get the engine running. |
| 05:15 | So for now, we just need some numbers that will get us going. |
| 05:19 | Usually we'll find that the idle area of the map will have numbers in the range of 20-40%, so for now, to get started, we can set the entire map to 30%. |
| 05:30 | If we're tuning on the Dyno, this would be enough to get us going, but on the road, we need to be able to run the engine across a wider range of rpm and load while we're getting going. |
| 05:39 | A flat map like this is likely to be too lean everywhere but idle. |
| 05:44 | What I'll do is build some shape into the map to match what I expect the finished map will look like. |
| 05:50 | This doesn't need to be super accurate right now. |
| 05:53 | Since we can expect fuel requirements to increase with load, I'll start by increasing the fuel numbers in each load row by 2%. |
| 06:02 | We can also expect to see fuel requirements increase as engine torque increases. |
| 06:08 | Most engines make peak torque somewhere around a third to a half of their rev limit, so I'll increase the fueling by 2% in each rpm row from idle to my estimated peak torque and then reduce it again. |
| 06:20 | This should give us an approximation of the fuel map shape. |
| 06:24 | Again, don't get too hung up on this as it isn't critical and there's no way the numbers will be perfect right now. |
| 06:32 | This shape we're adding to the fuel table will help us drive the car while we're getting the numbers dialed in perfectly. |
| 06:38 | This is all we should need to get our engine started and running. |
