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Practical Diesel Tuning: Fuel Impact on Diesel Tuning

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Fuel Impact on Diesel Tuning

07.21

00:00 - In this module, on our 2005 Duramax, this is a 6.6 litre, this is an LLY, it's a stock truck other than a very minor tune.
00:08 We're going to use switchable tuning today to explore how changing the fuel rate, separate of any other changes to the truck, is going to change power output and air/fuel ratio.
00:17 So first I'm going to direct you to the tune file and we're going to show you how I change those fuelling rates.
00:22 So let's jump into that.
00:25 First I want to draw your attention to the main pulse width table and the main pulse width table no pilot.
00:38 These tables are what the truck's going to be running in, the 90 mm³ and 100 mm³ table.
00:44 We're going to be running at about 160 mPa, so here's our pulse width.
00:50 OK so that's our base pulse width in the base file, then we're going to move to the DSP1 file.
00:57 So let's jump into how we made those changes to the tune file.
01:00 I'm going to draw your attention to the pulse width tables, 'cause those are where the changes are going to be made.
01:05 The truck's going to be running at 90 mm³ to 100 mm³ at full fuel and so we're going to look at the 160 mPa column which is the fuel pressure that we're targeting for max power and the 100 row for mm³.
01:17 And we're going to look at the injector on time in that cell.
01:23 The base file, we're at 1476.
01:36 In DSP1 we're targeting 1620, that's an increase of 10%.
01:48 And then as we jump to DSP position 2, we're going to see about 1725.
01:52 And that's an increase of another 10% over DSP1.
01:56 So stock, 10% up and then 10% more.
02:00 It'll be interesting to see how much more power we make and what the lambda does.
02:03 Let's jump in and start dynoing.
02:05 Today we'll be dynoing in fourth gear from 2000 RPM to 3450.
03:01 Now that we've finished the dyno test I'm going to go ahead and import the scan files, we'l look and verify that the fuel rate did indeed change, see if there's anything else interesting in the log data and then we'll check the dyno graphs.
03:11 In front of me I have the log files pulled up from those last three passes.
03:14 So first thing I'm going to do is look at the fuelling rates in the log files.
03:18 We'll start at 3000 RPM.
03:19 It's where the engine usually makes peak power and it's a good spot to compare fuelling rates and we'll also look at what the turbocharger's doing, draw your attention to the yellow line, you can see the pulse width's about 1544, The vane position's about 48.2.
03:35 That's a fairly tight squeeze on the vanes and the vanes are being squeezed to make 38 MAP so 23 pounds of boost.
03:44 Now the reason I'm looking at pulse width and not mm³ is because this ECU is maxed out at 100 mm³.
03:50 It doesn't calculate out past 100 mm³ so when we want to talk about fuelling rate, the things I'm looking for are fuel pressure and pulse width.
03:58 The injector nozzle tip is the only other thing that's going to determine the fuelling rate and that's static.
04:03 So as long as we have good fuel pressure which we do in this run, I'm going to look at the pulse width to compare and make sure that we're adding fuel.
04:09 Now let's move onto DSP position one or tune two.
04:12 Here on tune two we can see the pulse width, 1633, so we've stepped up in pulse width 10%.
04:18 I'll also draw your attention to the vane position.
04:20 Now notice that the turbocharger doesn't have to work as hard, in fact the vanes have gone from 44% in a previous run to 40% in this run.
04:28 So the vanes are opening to make the same boost we're again at 37.7 MAP or 23 pounds of boost.
04:34 Remember I told you that I wasn't going to change anything else, that means I didn't change timing, I didn't change desired boost, I didn't change desired fuel pressure.
04:40 Everything else is going to remain static except for the change in pulse width.
04:43 Let's move onto tune three and take a look at that one.
04:46 Tune three, yellow line, 1808 on the pulse width, the vanes are at 40%.
04:52 I would have thought they would have dropped a little bit but the data tells the story, 40%.
04:57 And again 38 pounds of MAP.
04:58 There's the changes in fuelling as advertised, shown in the log file.
05:02 Now let's take a look at the dyno graph and see how the power levels change and how lambda changes.
05:06 I have the dyno graph open and I have the three dyno runs compared to each other on the graph.
05:11 So let's see if the changes in horsepower match the changes in pulse width that I was talking about.
05:17 So on tune one we had 1550 microseconds, that turned out to be about 335 rear wheel horsepower.
05:23 On tune two we had 1650 microseconds, that turned out to be 345 rear wheel horsepower.
05:29 Interestingly that's about 6% more fuel and we got about 3% more horsepower.
05:35 I'll go into that in a second.
05:36 Tune three, 1808 microseconds, we ended up with 372 rear wheel horsepower.
05:43 So a significant jump from the 345 of the previous tune.
05:46 Now in that tune we added 9.5% more fuel from tune two to tune three.
05:52 We picked up 7% more horsepower.
05:55 So you're seeing kind of a theme here, we add more fuel, 10%, but we get 7% more horsepower, why is that? Well some of that fuel that we added, some of that pulse width that we're adding is added in injector latency.
06:09 So not all of it's fuel, some of it's injector on and injector off time.
06:13 Secondarily, we're not changing timing and we're not changing boost.
06:18 Now I wouldn't advocate changing boost at this level, you could see on the dyno graph that the air/fuel ratio is pretty well capped at 19.5.
06:24 In fact the only time it goes below 19.5 is at the start of the run.
06:29 This little red spot here indicates when I first tip into the throttle and the lambda comes below 19.5.
06:36 But quickly as the turbocharger spools up, the truck cleans up and comes back to 19.5 So we clearly have plenty of boost for this horsepower test.
06:43 Really what we're showing is the difference between changing pulse width and changing power.
06:47 To wrap it up, if you're going to change the fuelling rate by a percentage, expect the horsepower to go up by a similar percentage but less.
06:54 You may have to tweak with timing a little bit from there or look at the other elements of your injection event if you want to really capitalise on that additional fuel.
07:00 Simply adding fuel will get you more power but not as efficiently as the fuel you'd previously added.
07:06 Clearly adding more fuel gets you more power.
07:08 If you want to really take advantage of the extra fuel you're adding, you're going to need to look at timing and you're going to need to verify the boost is there.