Road Tuning: Step 9 - Optimising Tune
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Step 9 - Optimising Tune
07.36
| 00:00 | Now we've tuned our fuel and ignition, the last part of the puzzle is tuning our acceleration enrichment or transient fuelling. |
| 00:08 | Here we've actually got an advantage because doing this on the dyno is quite difficult because we don't have any feel for what the engine's doing. |
| 00:17 | While we do want to take input from our air/fuel ratio meter, we also really want to feel how the engine responds when we make sharp changes to the throttle. |
| 00:26 | First of all let's have a look at the tables or the parameters that are available to us in the acceleration enrichment menus. |
| 00:34 | First of all we've got our accel mode which tells the ECU which parameter to use for the acceleration enrichment. |
| 00:41 | Here we've selected TPS, and basically as long as one's fitted that's what we're going to want to use. |
| 00:47 | The next parameter that's important is our accel sensitivity which tells the ECU how much fuel to add for a certain rate of change of throttle position. |
| 00:58 | The higher this number is the more sensitive the ECU is to changes in throttle position. |
| 01:05 | Normally a number of around about 30 here I find works quite well in the Link ECU. |
| 01:12 | The main table that we're going to want to spend our time adjusting though is this accel clamp table and as you can see this is a 2-D table of acceleration enrichment versus engine rpm. |
| 01:24 | You can see at low rpm we've got larger numbers, and that tapers away until we've got nothing above four and a half thousand rpm. |
| 01:32 | That's because at higher rpm the air speed is higher and we don't actually need so much acceleration enrichment. |
| 01:39 | To tune this table what we want to do is drive the engine in each zone, and we want to hold a constant throttle just cruising, and then mash the throttle fully open and see how the engine responds and how the air/fuel ratio responds. |
| 01:54 | Using data logging to do this is really helpful to actually see what the air/fuel ratio does. |
| 02:00 | We're just going to do that now at 1,500 rpm and I'll show you how that works. |
| 02:08 | It's important before we ask for the acceleration enrichment, that we're cruising at a constant speed and a constant throttle. |
| 02:15 | Then I'll just go straight to full throttle. |
| 02:22 | We'll just stop and have a look at what happened there in the data logging. |
| 02:29 | If we zoom in on the area we're interested in you can see where I've gone from closed throttle to full throttle. |
| 02:35 | This here is the acceleration enrichment spike. |
| 02:38 | What we can see is before the acceleration enrichment we're cruising with a lambda of point nine nine seven, basically our target lambda one. |
| 02:46 | You can see we've got a small lean spike here just before the air/fuel ratio actually moves rich. |
| 02:54 | That's actually pretty good and the engine response was pretty clean. |
| 02:59 | There was no bogging. |
| 03:00 | There was no hesitation. |
| 03:01 | It was quite smooth. |
| 03:02 | This small lean area here to me that would suggest that at 1,500 rpm the acceleration enrichment table could do with a little bit more acceleration enrichment in there. |
| 03:13 | I'd go back and add 10 numbers to that table and try it again and see how it responds. |
| 03:20 | One thing I want to point out here is you can see there's quite a delay. |
| 03:24 | We've gone to full throttle here, but it's not until this point here, a few tenths of a second later that the air/fuel ratio has actually moved richer and taken on that acceleration enrichment. |
| 03:38 | It's important to understand that particularly at low rpm there is going to be a little bit of a delay between the engine's air/fuel ratio changing and what our wideband will pick up. |
| 03:51 | That's why I say it's quite important to use feel for tuning this table as opposed to relying solely on the wideband meter. |
| 04:00 | We'll just go through now and tune this table. |
| 04:03 | You can see how I do it. |
| 04:05 | First of all we'll start by adding a little bit more fuel into that low area which we've just talked about. |
| 04:11 | I'll just test that again. |
| 04:25 | I was happy with what happened there at 1,500 rpm. |
| 04:28 | We're just going to test that now again at 2,000 rpm. |
| 04:38 | To me that looked like we went a little bit lean. |
| 04:41 | Again the engine still feels quite smooth, but I'll just try adding a little bit more fuel and we'll do that again. |
| 04:49 | The air/fuel ratio response there was still a little bit lean so go richer again. |
| 04:59 | Now we've got pretty good response at 2,000 rpm. |
| 05:04 | We'll just turn around and we'll move up to the two and a half thousand rpm row. |
| 05:09 | Again, just like tuning the main fuel table, you start to get a feel for the numbers that we need and I would look at that. |
| 05:17 | In two and a half thousand rpm, we've currently got a number of 15 in there. |
| 05:20 | I'd probably increase that to 20 just to sort of interpolate the numbers I've already got at 1,500 and 2,000 rpm. |
| 05:28 | We'll drive at two and a half thousand rpm now. |
| 05:33 | That was at 20 in there worked out really well. |
| 05:37 | We'll try 3,000 rpm which is also good. |
| 05:47 | Three and a half. |
| 05:54 | You can see as we get up in the rpm, and the air speed through the engine increases, we are responding much quicker. |
| 06:04 | The air/fuel ratio is dropping to our target much quicker. |
| 06:07 | At 4,000 rpm So two and a half percent at 4,000 rpm is good. |
| 06:15 | We'll just try at four and a half thousand rpm. |
| 06:18 | I'll just turn around. |
| 06:46 | So four and a half thousand rpm was also good. |
| 06:49 | We've data logged that and you can go back and review that file and see how the air/fuel ratio has responded on each of those accel requests. |
| 07:00 | You may see some small spikes like this here where you still want to make further changes. |
| 07:06 | If we look at the higher rpm ones, you can see how the air/fuel ratio has dropped almost straightaway to our target even though we've got small amounts of enrichment. |
| 07:18 | Again, while the wideband is useful in how I'm going to tune these tables, it's really more important as to how the engine feels on response. |
| 07:28 | We're looking for smooth acceleration with no hesitation and no bogging. |
