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Practical Reflash Tuning: Step 4-B: Speed Density System Calibration

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Step 4-B: Speed Density System Calibration

13.46

00:00 - With our mass air flow sensor calibration now correct, we've still got a little bit more work to do.
00:05 In this case what we're going to now do is look at how we can dial in the speed density side of the Ford ECU's operation.
00:12 Now as we've already mentioned briefly, the ECU primarily uses the mass air flow sensor as its input but it also has a background speed density system that's used for particular situations such as transient, where it can respond potentially quicker than the mass air flow sensor.
00:30 I think it's fair to say there is a lot of confusion and misunderstanding about the speed density subsystem in the Ford ECU, particularly because it doesn't use a conventional volumetric efficiency table as we may be used to in the aftermarket.
00:44 This is because of the complexity of the Ford ECU.
00:48 And in fact it uses continuously variable cam control, we end up with the volumetric efficiency of the engine varying as the cam timing moves.
00:58 So for this reason the Ford ECU uses a similar principle to late model GM ECUs where the speed density system is calculated using some pretty complex quadratic equations.
01:10 Let's jump into our software and we'll see how the speed density subsystem looks.
01:14 So we're on our speed density tab under air flow and we can see that we've got a number of tables.
01:21 For example here we've got a set of tables labelled offset.
01:25 We've got a set of tables labelled slope.
01:27 And we've got another set of tables labelled quadratic term.
01:30 Obviously as we can see these are relative to our mapped point.
01:35 Now traditionally this has been quite difficult for us to tune in the aftermarket.
01:40 Recently HP Tuners have included a speed density calculator right within the tuning software, we'll have a look at that here, from the edit menu, we'll just choose the speed density calculator.
01:51 And this allows us to move through the different tables relevant to our mapped point, as we can see here.
01:57 And now we've got a table that we can make some kind of sense of.
02:01 We've got our manifold pressure on the vertical axis, and we've got engine RPM on the horizontal axis.
02:09 So this makes it a lot easier, we can make adjustments within these tables for the relevant mapped point.
02:14 And then we can automatically have the calculator calculate the new coefficients, they'll be updated in the calibration, we can then load that into our ECU.
02:25 Now it's important to mention here that this particular ECU, because it does primarily rely on the MAF, a lot of tuners will completely ignore the speed density system.
02:36 And this isn't uncommon, and in a lightly modified vehicle, it's also probably not actually gong to cause you too much grief.
02:44 Once we start getting into more serious modifications though, overlooking the speed density subsystem is likely to end up causing you some problems.
02:52 So for the sake of completeness we are gonna go through a demonstration here of how we can do this.
02:57 Now there's one thing we do need to do before we get started and that is to re enable the cylinder air anticipation.
03:05 So we'll go back to our general tab here and we can see that we've already actually done this.
03:10 You'll recall that while we were setting up our tune so we could calibrate the mass air flow sensor, we'd disabled cylinder air anticipation.
03:16 We can see that I have now got this re enabled.
03:19 Now also to give us some work to do here since we are dealing with a calibration from Roush that's already suited to the supercharger, I've previously gone through and I've actually made some adjustments to the speed density tables so that there actually is some error.
03:35 Otherwise we wouldn't have too much to display.
03:37 So the principle here is that what we're looking for is the calculated manifold absolute pressure inside our scanner.
03:45 And we want to compare that to the measured manifold absolute pressure.
03:49 In an interesting angle from Ford, this particular engine is not fitted with a manifold absolute pressure sensor and instead the MAP value is calculated or inferred.
04:01 So if our speed density subsystem is all correctly calibrated, then the calculated MAP value should match the MAP value that we've got on our dyno.
04:11 Now in this instance our job is made a little bit trickier because I can't bring manifold absolute pressure into our scanner.
04:18 So instead we're actually gonna have to do this manually which is gonna take a little bit more work.
04:23 What we're going to do is use the dyno data to give us a real MAP value.
04:29 And we're gonna compare that to the calculated MAP value at a range of different points at a fixed RPM.
04:34 And then we're going to use a spreadsheet to calculate the error.
04:37 We'll apply that into our speed density tables.
04:41 Alright so let's get up and running and we'll start scanning some data.
04:48 Alright we've got our engine up and running, we're scanning some data now, but before we actually get stuck in, we'll just have a little talk about what we're going to be doing here and how we're gonna go about gathering our data.
04:59 And the way we're going to do this is really gonna be dependent on how extensive the modifications are to your engine.
05:06 Now if you are only dealing with a lightly modified engine, maybe something where an intake and exhaust system has been fitted, then it's fair to say that this is not likely to create dramatic changes to your volumetric efficiency.
05:20 So a way of speeding up this process is that we can fix the engine RPM in our dyno and then we can go through and plot the calculated MAP versus our actual MAP for that one RPM column.
05:33 And then basically we can apply that error to our entire speed density table, and we can then apply the same error to all of our mapped point speed density tables.
05:44 Essentially here we're assuming that any error that we've seen at our measured point is going to also be the same kind of error right through our entire VE table at each mapped point.
05:55 Now of course that's not always going to be the case.
05:57 But this is the fastest way of going about calculating and tuning the speed denisty subsystem.
06:04 Now if you are making more dramatic changes to your engine where there are much more significant effects on the volumetric efficiency, you're going to need to be more thorough.
06:14 Now you obviously could spend a lot of time here if you're going to adjust every single point.
06:20 Instead what I would do is take a more measured approach and choose maybe three or four RPM ranges to gather your data.
06:28 This is going to give you a good idea of the shape of the errors that will need to be corrected.
06:34 The approach obviously depends on your engine modifications, but the technique is going to be exactly the same, is what we're about to look at.
06:43 So let's get started, we're running at around about 1600 RPM.
06:46 I'll just bring the RPM down a little bit here to about 1500.
06:49 And what we want to do is start by reducing our manifold pressure as far as we can.
06:56 So the parameter that we are logging here is our calculated manifold absolute pressure.
07:03 You can see at the moment that's sitting about 45, 46 kPa.
07:06 And we've also got that same parameter being logged up here in our chart.
07:12 So we can see visually how that's going to change.
07:14 So what we want to do is get ourselves to basically the lowest point that we can hold on our dyno.
07:20 Seems to be around about 50 kPa.
07:22 And what I'm going to do here is bring up this spreadsheet which I've set up.
07:26 It's really basic, all we've got is three columns here.
07:30 We've got our calculated MAP.
07:32 We're going to enter this directly from our scanner.
07:34 We've got our actual MAP and we're going to be taking the number from our dyno.
07:38 So we can see on our dyno screen here, we've got our manifold absolute pressure being shown sitting currently at about 44 kPa.
07:47 So we're gonna enter those two values, and then we also have a calculated error that's going to pop up here.
07:54 This calculation is really straightforward.
07:57 All we're looking at is the difference between our calculated and our actual MAP and then we're representing that as a percentage.
08:04 So let's get started, what I'm going to do is go up in 10 kPa increments, and we're going to gather data at each of those points.
08:11 We'll just discuss the first one, so I'm just going to apply a little bit more throttle until we can get quite accurately up to 50 kPa, so that is our calculated manifold pressure point.
08:21 Now we'll just hold that there at 50 kPa.
08:24 And we can see that we've got around about 45, 46 kPa on our dyno, it's moving around a little bit, we'll enter 46.
08:33 And we see that the calculated error shows that the ECU is over calculating manifold absolute pressure by in this case about 8%.
08:43 Alright so we're now going to go through and we'll complete this right up to the point where we are at wide open throttle, in 10 kPa increments.
09:19 OK so we've gone through and we've gathered some data there and we've managed to get data between 50 kPa and we were just under 140 kPa, 138 right at wide open throttle.
09:31 So we can see that we've got a range of error values there.
09:35 Maximum error right down at low manifold pressure, we've got about 8.7% as we've already discussed.
09:41 Interestingly enough, around about 80 to 90 kPa the calculation was matching quite well and then we've sort of settled around about 5% to 6% as we've increased our throttle opening.
09:55 So what we can do is then use this data to make some corrections to our table.
10:00 Now just for simplicity for this demonstration we're just going to take an across the board approach here.
10:06 We'll basically average out those errors and we're going to apply a 5% change to our speed density tables.
10:13 So let's go and see how we can do that, we'll head back across to our editor.
10:17 We're going to bring up our speed density calculator.
10:21 And what we need to do is do this for each of our mapped points.
10:24 So we're starting here with mapped point zero.
10:27 So what we're going to do, remembering that we made our changes here at 1500 RPM but as I've discussed, we're just going to apply these broadly across the entire VE table.
10:37 So we're going to highlight the entire table and I'm going to multiply by 1.05 Once we've done that, you can see that the air flow to coefficients box becomes active.
10:49 We'll click on that and that will then calculate the new coefficients for that mapped point.
10:55 What we'll do is now repeat this process for mapped points one through to four.
11:04 Alright we've made that adjustment to our five mapped points.
11:08 And we can now close down our editor.
11:11 If we head back across to our speed density tab we can see that the coefficients have now been altered by that speed density calculator.
11:20 What we're going to do now is save our calibration and we're going to flash that back into the ECU.
11:26 And we'll go through and do another test and see the effect of those changes.
11:32 Alright we're back up and running so let's go through now and we'll have another look and see the effect of those changes.
11:37 Right now we're sitting at just over 50 kPa and we'll see that our dyno's showing around about 48, 49 kPa, so we know we're already pretty close.
11:47 We're gonna go through and we'll check each of the same points that we checked for our first test.
12:20 OK so we've gathered some data there from our first round of changes to our speed density subsystem and straight away by checking the error values we can see that we are much closer, our error is much smaller than what we previously saw.
12:33 Another thing you may notice here is that the maximum manifold pressure that we got to this time was a calculated value of 126 kPa at wide open throttle.
12:41 This is simply because the manifold pressure was being over calculated with our previous speed density tables.
12:50 Now that we've corrected those, the values are much more realistic, so that's why we're not getting to those same values.
12:56 Now just like our mass air flow sensor calibration, calibrating the speed density system is an iterative process.
13:02 So you'll generally expect to take two to three attempts to get these tables calibrated correctly.
13:09 It's also important to understand just like the mass air flow sensor, we don't need to beat ourselves up trying to get the calculated MAP to be absolutely perfect.
13:19 Generally I'm looking for a correlation of about plus or minus one to two kPa.
13:24 If I'm within that range then I'm going to be quite happy.
13:27 So at this point we've got our mass air flow sensor calibrated correctly, and we've got our speed density subsystem calibrated correctly.
13:35 These are two of the most important aspects of the Ford ECU and we need to have these right.