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Practical Reflash Tuning: Data Logging

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Data Logging

10.10

00:00 - Possibly the most daunting aspect of reflashing for those coming from a stand-alone, ECU tuning background, is the inability to make tuning changes in real time.
00:11 With a conventional stand-alone ECU, we can adjust the numbers in the fuel or ignition tables and instantly see the result of these changes on the dyno.
00:23 As we discussed earlier, in some instances live tuning may be an option for some ECUs, however the much more common technique is to take a data log from the ECU and then make changes based on this data.
00:38 This means that data logging plays a critical part in successfully and accurately being able to reflash a factory ECU.
00:47 If you're buying a commercial reflashing package, then it will come with data logging software, while in the open source community there are various logging options available that you'll need to download.
01:00 Some of these may be free, while others may require a modest investment.
01:05 You'll see the data logging in action in the Worked examples later in the course, but in this module we'll discuss what we're trying to get from our data logs, and what parameters we may want to look at.
01:19 One aspect to consider is that there may be a huge amount of data available that we can potentially log, and the data we need to view will depend on the specific tuning task we're completing.
01:32 For example, the parameters relevant to optimising the idle control won't be much use when you're trying to optimise the ignition timing, and vice versa.
01:43 It might sound sensible then to simply log all the parameters available, and then you're certain to have access to the data you need.
01:52 The problem with doing this is that there is often a limit to how much data can be sent through the OBD2 port, and if you log multiple parameters this can result in the parameters being logged at a slower rate that isn't useful for our purposes.
02:09 For fast-moving input such as engine speed, manifold pressure, or air fuel ratio, we need a reasonably high logging rate, of perhaps 20 to 25HZ as a minimum to get useful data.
02:22 Slower-moving inputs such as inlet air temperature, or engine coolant temperature, don't move so quickly and hence a slower logging rate of perhaps 1 to 5HZ is acceptable.
02:35 The amount of control over the logged parameters and the logging rate will depend on the vehicle you're tuning, as well as the logging software you're using.
02:44 The actual parameters that are available to log will depend on the ECU you're working with, and not all parameters are going to be available on all ECUs.
02:56 The actual parameters you want to log are often defined by what's referred to as a PID, which stands for parameter ID.
03:04 And these PIDs are used by the data logger to request data from the vehicle's ECU.
03:10 While all manufacturers are required to make available certain PIDs, mainly for the purposes of checking emissions compliance, many other PIDs may be available depending on the manufacturer.
03:24 While it's not possible to list every parameter that may be useful to log, some of the key ones would include engine speed, mass air flow, engine load, throttle position, ignition timing, knock feedback, fuel trims, and commanded air/fuel ratio or lambda.
03:45 In particular, logging engine load and engine speed will allow you to see where in a particular map the ECU was accessing at a certain point in the data log.
03:57 Ignition timing and knock feedback are valuable parameters to aid optimising the ignition timing, although I'll point out that how the knock feedback or knock detection is handled and logged will vary dramatically from one ECU to another.
04:13 As well as the internal PIDs that we want to log, it can be useful if we can also input an accurate external wideband air/fuel ratio metre, so we can see exactly what the air/fuel ratio is doing at any point in the log file.
04:29 In some instances, an external wideband metre can be connected directly to the hardware interface between the OBD2 port and your laptop, while in other instances it can be connected to an unused input on your ECU, and then read through the OBD2 data stream.
04:48 Let's stop now and have a brief look at what you may be able to expect from some of these logging systems.
04:56 So here we're going to have a quick look at an example of what we can expect from a modern data logging package, and the example we're looking at here is from HP Tuners, this is the VCM scanner software, which we can use with GM and Ford vehicles.
05:12 Now, I've got some live date being displayed here, and we'll just have a quick look at what we've got available.
05:17 On the left hand side of the screen here you can see we've got a range of channels being displayed, so these are the PIDs that we're currently scanning from the ECU.
05:29 And there's a range of data there that's going to depend on exactly what task we're doing.
05:33 Here you can see for example we have our engine RPM.
05:36 Below that we have our engine coolant temperature, and our intake air temperature.
05:42 Useful parameters that we can use to decide where exactly in the ignition or fuel tables the ECU is accessing, we have our mass airflow here in grammes per second.
05:54 I'm also looking a little bit further down here at our cylinder air mass, and cylinder air mass is one of the axis that the GM PCM uses for some of its tables.
06:07 So we can see from that and engine RPM exactly where we're accessing.
06:12 We've also got here our commanded lambda, so this is the lambda that the PCM is currently asking for, and I've also added in here, which you can see highlighted in blue, an external wideband metre so we can actually see what the current measured lambda value is.
06:29 So this is really useful when we're looking at scaling both our MAF and our injectors.
06:37 So to the right of that we've got our chart logger.
06:40 So this shows a number of parameters and groups and you can see what we've got, scrolling along here while the engine's idling.
06:46 We've got our RPM displayed up here, and when the engine's actually at speed we're going to see, when the car's at speed, we're going to see our wheel speeds as well.
06:55 We've got some data here that shows our mass air flow in grammes per second, we're also looking at our manifold absolute pressure at the same time.
07:05 The next chart down we have our current ignition advancer.
07:10 At the moment you can see the advancer's moving around and the ECU is using the ignition timing to help control the idle speed.
07:16 The red parameter, which currently is sitting at zero is our knock retard, so we're going to use this to help tune the ignition tables and decide when the ECU is detecting knock.
07:27 If we move down here we've got our short term and long term fuel trims, so again we're using this to help us decide how close the MAF scaling injector scaling is.
07:36 You can see at the moment the long term fuel trims are disabled, so they're sitting at zero.
07:42 The next chart we've got our commanded lambda versus our measured lambdas.
07:48 This is really nice to see exactly how closely our measured lambda is tracking that target.
07:54 And finally at the bottom we've again got our cylinder air mass.
07:58 So let's load up a log file now so we can have a look at some data during a ramp test.
08:04 And if we want to move through the data we can just grab and drag to the area that is interesting to us, and you can see here we've got a run now that we've just done on our dyno that goes all the way out to 6200 RPMs, so you can see both our engine RPM and our groundspeed are moving.
08:23 In our ignition table here, our ignition chart, you can see that we have seen a very small amount of knock retardant, that's the little red blip here that we can see at the bottom.
08:33 We can see that if we look at our commanded versus our measured lambda that again this is tracking very close to our target, so a really powerful way of seeing exactly what's happening during a run.
08:45 The VCM scanner also gives us the ability to create some histograms, and this allows us to analyse the data in another way.
08:52 So here we've got a histogram set up, and you can see there on the load axis we have our cylinder air mass in grammes per cylinder, and we obviously have our engine RPM on the horizontal axis.
09:03 So, we can set this up and during the ramp run the scanner software will log in this case our current spark advance versus where exactly in the table the PCM was accessing at any particular time.
09:17 So you can see under a wide open throttle, ramp run conditions, how the PCM tracks through the table.
09:25 This is going to help us decide exactly where to make changes in the spark advance table.
09:31 Likewise, if we have any ignition retard, that will be displayed on our spark retard histogram.
09:37 So it's very powerful, also incredibly flexible, we can set this up to show just about any parameters we want.
09:44 Now, obviously the functionality and the options that you have available are going to be very dependent on the exact software that you're using, and also dependent on the vehicle that you're reflashing.