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Practical Reflash Tuning: Worked Example

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Worked Example


00:00 - The final step of our six step process is to confirm everything that we've seen on Dyno, out on the road, or the racetrack.
00:06 Out in the real world.
00:08 Now, I know this is a step that many tuners will choose to overlook.
00:12 However, I've seen many instances where, once we've got the car off the Dyno, I've seen slight differences in the air fuel ratio over what we saw on the Dyno.
00:22 Or, alteratively, the engine may be a little bit more prone to detonation out on the road, or the racetrack.
00:28 Now, since we don't drive or race our cars on the Dyno, obviously we're much more interested in making sure the tune is correct, or perfect, out on the road or the track.
00:38 Now, for the purposes of this demonstration, we're going to be using racetrack.
00:43 Obviously this is the ideal situation, since we don't need to worry about oncoming cars, we don't need to worry about other traffic or pedestrians.
00:52 However, with the process of reflashing, we can concentrate primarily on driving the car, making sure that we're controlling the car, and we are aware of our surroundings.
01:03 We don't really need to be paying any attention to our laptop while we're actually driving.
01:08 Instead, what we're going to be doing is scanning the ECU while we're driving, then we're going to be analysing the results of that scan data in the pits, or on the side of the road, in the relative safety of that area, where we don't, again, need to worry about other vehicles.
01:25 This is very important.
01:26 Obviously, safety is paramount here, and we do need to maintain 100% control of the vehicle at all times.
01:35 Now, for our testing purposes, I do have my wide band air/fuel ratio metre suction cupped to the wind screen.
01:42 Now, this is handy because I can just glance at this out of my peripheral vision while I'm driving the car.
01:49 Particularly with a highly stressed engine, when we're doing full power acceleration testing, I can just glance at this out of my peripheral vision while we're accelerating at full power, and just take note of the air/fuel ratio.
02:02 I can still concentrate primarily on making sure that I'm in control of the car, but I can just glance occasionally at this metre, and if I see anything I'm not happy with, either the air/fuel ratio is too rich, or too lean, in that case I can abort the run, make the necessary changes, and come back and try again.
02:20 It's always safest to do this, rather than persevering with a condition that is deemed to be unsafe.
02:27 Now, there is several things that we're going to be looking at while we're turning our car, or testing our car, on the racetrack.
02:35 The first of these is, what we want to do, is simply go for a drive, and confirm that under normal cruise conditions our short term and long term fuel trims are within a safe tolerance.
02:47 Generally here I'm looking for a tolerance of around about possible minus three to five percent.
02:53 Obviously, the closer we can get these short term and long term fuel trims to zero, the better.
02:58 But, understand that we are always likely to see some slight fluctuation from day to day and even dependent on engine coolant temperature, and intake air temperature.
03:10 So, we're going to be trying to get those within that range.
03:13 Again, when we're doing this, it's always best to have our fuel trim slightly on the negative side, rather than slightly on the positive side.
03:22 This means that naturally the engine is running slightly rich, and obviously that's the safest situation.
03:27 When we're taking note of our fuel trims, this is going to depend on whether or not we've left our long term fuel trims enabled.
03:35 Which, for this particular worked example, we have.
03:38 Remember that the total trim is going to be the sum of your current short term and long term fuel trims.
03:46 Okay, so let's go for a drive, and what we're going to look at initially is those short term and long term fuel trims.
03:53 This is going to give us a guide as to how well we've done with our mass air flow sense of tuning, or our speed density tuning, if we're using a speed density system.
04:04 Let's head out on the track now, and we'll see what we've got.
04:07 Now, one of the very important lessons to learn when we're testing the car on the road, is that we always want to allow the engine to run for long enough, to get rid of any heat soak.
04:19 Particularly there while I was talking, we've got the engine idling, and this is going to end up with both the engine coolant temperature, the under bonnet temperatures, and the intake air temperatures, much hotter than what we would traditionally expect to see when we're running the car out on the road or the track.
04:36 So, the very first part of my process here before I take any notice at all of the data, is to simply do a full lap of the track, and allow our engine coolant temperature and our intake air temperature to come down to what I'd consider to be, or what I'd expect to see, under those normal operating conditions.
04:55 So, we're just going to do that now.
04:57 Okay, so we can see now that our engine coolant temperature is sitting at 91 degrees centigrade, and our intake air temperature is sitting at 17 degrees.
05:05 So, now that I've got our engine at a normal operating temperature, we can start taking some notice of the data on our laptop.
05:12 What we can see is that, when I'm not under deceleration fuel cut, so, when I'm actually on the throttle and I'm driving, we can see that our short term and our long term fuel trims are staying very, very close to zero.
05:23 So again, this is indicative of a good calibration for our mass air flow sensor.
05:29 Now remember, in this particular instance, we are running the GM blended system using both the mass air flow sensor as well as the virtual volumetric efficiency subsystem.
05:40 However, primarily under steady state conditions, the fuel,load calculation is based off the mass air flow sensor.
05:49 So, the calculation will be more sensitive to our mass air flow calibration, than our speed density, or virtual VE subsystem.
05:59 The virtual VE subsystem is primarily there more for accuracy under transient conditions.
06:06 So again, we're just driving along, and you can see that our trims are sitting still, very, very close to zero.
06:12 So we know that the results of our mass air flow sensor scaling in the cruise areas of our mapping are very good.
06:21 Particularly for a street car, the area that we're going to be most interested in, is the idle areas and also our scaling out in the cruise areas.
06:32 This is simply because this is the area of operation that the engine is going to spend most of its time in.
06:39 So, we've looked at this now.
06:41 We're happy with our fuel trims, we know that the ECU has accurate data, providing it with the correct mass air flow so that it can correctly provide the right amount of fuel, and achieve our commanded air flow ratio.
06:56 Which obviously for cruise, in closed loop is our stoichiometric AFR 14.7:1.
07:02 The next step of our process is to have a look at our tuning and the wide open throttle.
07:07 Here we're looking primarily at two aspects.
07:10 We're again looking at our fuel control, how close our air/fuel ratio is to our commanded air/fuel ratio.
07:17 We're also looking to see if the engine is suffering from any knock under those conditions.
07:23 What we want to do here is to use a high enough gear to provide a reasonable amount of load to the engine.
07:30 We also need to balance this with the fact that, obviously the higher the gear, the faster we're going to be going by the end of our test.
07:37 In this case, I'm going to use the manual function and our six speed automatic gear box.
07:42 We're going to run this test in third gear.
07:45 What we really want to do is sample the full range of the engines rev range.
07:50 I'm going to start from around about 1200 RPM, and I'm simply going to go to full throttle on the longest part of our track, and see what our results are.
07:58 Let's do that now.
08:09 Okay, so that's our test complete there.
08:12 Now again, we've got the laptop running there while I've been doing that full power test.
08:18 I didn't need to watch the laptop.
08:21 I didn't need to be focusing on what the laptop was doing.
08:25 I'm simply concentrating on controlling the car, making sure that I'm in the middle of the racetrack, and that nothing's going wrong.
08:34 As I've mentioned, I can glance occasionally at the air/fuel ratio metre suction cupped to the windscreen, so that I can check and make sure that my air/fuel ratio is somewhere I'm happy with, and obviously, as I've mentioned, if the air/fuel ratio is outside of the range that I'm comfortable with, I can simply back off the throttle, abort the run, and then we can make some changes, and come back and try again.
08:59 Now, we've returned to the pits, so let's analyse the data from that run and see what we've got.
09:05 Okay, so here's the results of our full power acceleration test.
09:09 So, we've got, again, our RPM at the top here.
09:12 You can see at the start of the run I've started to roll into the throttle around 1500 RPM, and I've managed to get through to full throttle at about 2400 RPM.
09:22 Now, we obviously do need to be a little bit careful here with traction as well.
09:27 Particularly with a super charged LSA engine.
09:29 This is another balancing point we need to consider when we're choosing the gear that we're going to use.
09:35 Obviously in the lower gears, the engine is going to be producing, or the torque multiplication through the gear box means that the engine is going to be transferring more torque to the rear wheels, hence the car will be a little bit more prone to wheel spin.
09:49 So, if we use a lower gear, perhaps first or second, we're obviously going to end up with problems with wheel spin.
09:56 As I've mentioned, if we're using a higher gear, we're going to end up with a higher terminal velocity by the time we've hit the rev limiter at the top of the run.
10:05 Now, in situations where we're really struggling with control over wheel spin, what we can do is perform our test in two parts.
10:13 So, in this case, where you can see that we've only really been able to get to full throttle here at 2400 RPM.
10:20 If I wanted to do another test and look at that lower range between 1500 and 2500 RPM, I could have done an acceleration test, just like you saw me do there, but using fourth gear.
10:32 Now, obviously that would have my terminal velocity exceptionally high, and I'm going to run out of racetrack before I get to the rev limiter.
10:40 But, for that test, I could simply look at the area between 1500 and perhaps 2 1/2 to 3000 RPM, make sure that area is okay, and then we can complete the test as we've just seen here, in third gear, to look at the rest of the rev range.
10:55 So let's look at that however.
10:56 You can see that if we look again at our RPM, right at the top of the run we actually hit the rev limiter at 6200 RPM.
11:05 We know that we've got through our full range.
11:08 If we look at our throttle position here, you can see that throughout the run, we are at maximum throttle, so this means that we were at full throttle.
11:17 We've got a good sample of data for this particular log data.
11:22 Now, there's two aspects we're going to be looking at here.
11:25 The first we're going to look at is our air/fuel ratio.
11:28 We want to check how closely our measured air/fuel ratio has matched our commanded.
11:35 You can see that throughout the run, our air/fuel ratio is generally within around about 1% of our target.
11:43 It's very, very close.
11:44 Obviously, if we've done our job correctly on the Dyno, this is exactly what we would expect to see.
11:50 So, no real surprises here.
11:52 A couple of things to be aware of, and again, really this doubles up on what we've already talked about on the Dyno.
11:58 We can see a little bit of lag here, where the engine, or the ECU, has first transitioned into power enrichment mode.
12:09 We can see that our commanded equivalence ratio drops to 0.80, just as we transition into power enrichment.
12:17 We can see that momentarily at this point, our measured air/fuel ratio still sits at stoichiometric metric, 0.99 lambda.
12:25 We can see just this little bit of lag before our commanded air/fuel ratio, and our measured match.
12:31 Now this is not something to worry about.
12:33 We're always going to get a slight delay on this transition to open loop to power enrichment.
12:39 This is to be expected.
12:41 Likewise, generally when I'm making large changes to throttle, as I've gone into full throttle here, I'm not again going to be taking too much notice of the accuracy of our air/fuel ratio control at these points.
12:54 This is because at this point, when we're making sharp changes to our throttle, we're also going to have the effect of our transient enrichment coming in.
13:04 So, I'm not going to be too worried if I see slight changes where we're slightly rich or slightly lean here.
13:10 What I'm really looking for is that the air/fuel ratio over the entire range of our wide open throttle run, once we've reached full throttle, and everything has reached equilibrium, is okay.
13:22 And, as you can see, it is.
13:24 So, we're happy with that.
13:25 The other aspect we want to look at, of course, is the activity from our knock retard.
13:31 So, our knock control subsystem.
13:33 As you can see in this case, right through our run, if we look at our spark and our knock retard, we have no knock retard activity.
13:42 This is obviously the ideal situation.
13:45 This is exactly what we want to see.
13:47 Now, in this situation, where I've got this sort of a result, where we have absolutely no activity from our knock retard subsystem at all, I would actually be inclined to try adding perhaps one more degree through the entire wide open running area.
14:04 This is a problem we see with some Dyno cell constructions.
14:08 We may find that the Dyno cell results in the ambient air in the room being a little bit warmer, a little bit hotter, than what we can actually see out on the road, or the racetrack.
14:19 So, in these situations, we can find that the engine will actually be more prone to detonation on the Dyno, than what we can see on the road.
14:30 The flip side of this is, sometimes the way the engine is loaded on the road, and the temperatures that it will see out on the road, or racetrack, particularly if we've got an intake system that tends to draw hotter air from the engine bay, we may find the opposite situation occurs, where the engine is more prone to knocking on the road.
14:50 Either way, this is why we're performing our road test.
14:53 We want to make sure that the engine is not suffering from knock, or detonation, when we're out in the real world, driving the car, as it will be used.
15:04 At this point we've looked at two aspects of our tune.
15:07 We've looked at our control over the air/fuel ratio, and the idle and steady state cruising conditions.
15:15 We've made sure that we're comfortable with the trims.
15:19 Again, just aiming for short term and long term fuel trim sums to be within a range of plus or minus 5%.
15:27 Generally, if we're going to choose, we want to make sure that our trims are slightly negative.
15:33 With our calibration, we have good control over our short term and long term fuel trims, they're within our happy range.
15:41 Next we have checked on the wide open throttle, and we know that on the wide open throttle we've got good control of our air/fuel ratio.
15:48 So this really confirms that our calibration for our mass air flow sense of scaling and our speed density, or virtual VE subsystem, is accurate.
15:58 Then, of course, we've also confirmed that our engine isn't suffering from detonation.
16:03 Now, at this point if we do have any errors, we're simply going to correct them in the same ways that we've already looked at on the Dyno.
16:12 So, particularly if we've got errors in our air/fuel ratio, we've got a richer or leaner air/fuel ratio than what we're commanding, we'd address this by either modifying our virtual VE subsystem, or, our mass air flow sensor calibration, depending on how you're running the PCM.
16:30 Now, obviously if you're running a MAF only calibration, this is where we're going to make changes.
16:34 Likewise, if you're running permanently in speed density, then the virtual VE tables are where we're going to be making changes.
16:42 In our case, where we've got a blended system, provided we've done our job correctly on the Dyno, under the steady state conditions as I've mentioned, the PCM is going to be relying more on the MAF input, than it will be on the virtual VE subsystem.
16:58 So generally, if we've got very small errors, I will make these changes to the MAF scaling, rather than going back through both the mass air flow sensor and the virtual VE scaling.
17:09 Okay, so our job's not quite done yet.
17:12 There's one other aspect that I like to look at when we're out on the road or track.
17:16 That's the transient response of the engine.
17:19 So, this is the response of the engine to sharp throttle inputs.
17:22 I also like to make sure that we're not seeing anything in the way of knock or detonation creeping in during gear changes.
17:30 The other thing that I like to look at here is what's going on at medium load, in terms of our knock control.
17:38 What I mean by this is, we've looked now at cruise, where we're obviously under very light throttle application, and we've looked at wide open throttle, and we know we've got no knock occurring in either of those scenarios.
17:50 However, we're also going to want to investigate, what we're going to see, or how the engine's going to respond, when we're using a little bit more load.
17:59 So, this would be as if we're accelerating at part throttle, or perhaps going up a slight hill with a little bit more throttle on board, where we're starting to move the engine into positive boost pressure.
18:11 So, we can check all of this out on the track and we can make changes as we need.
18:17 Let's head back out on the track and we'll see how we can do that.
18:21 As usual, before we scan any data and take any notice of the data, we want to make sure that we've eliminated any heat soak in our engine.
18:29 So, we've done that.
18:30 Now what we're going to do is simply drive a couple of laps around the track.
18:34 This time I'm going to drive the car a little bit harder.
18:37 I'm not really concentrating here on using full power, but I want to use a little bit more acceleration, a little bit more throttle, to put the engine under a little bit more load.
18:46 So this is going to let us sample a wider range of the engine's operating range.
18:50 Then, we're going to be looking at the histogram for spark retard.
18:55 What this is going to allow us to do is see if the engine is suffering from knock, and the spark retard system, the knock retard system, is being used in other parts of the engine's operation, other than cruise and wide open throttle.
19:10 This is giving us data now doing this.
19:11 What we want to be doing is concentrate on using low to moderate throttle.
19:17 We don't want to be going to wide open throttle.
19:19 I'm using somewhere around half to 2/3s throttle at the most.
19:23 What I'm really concentrating on here is using the mid range of the rev range.
19:30 In the region of perhaps 1500 to 2500 to 3000, this is the sort of area of the rev range that the engine again, we'll see when it's being driven, slightly harder on the road or the racetrack, but not what we're going to be operating in under wide open throttle.
19:47 Okay, so once we've got some data, we're going to head back to the pits, and we'll have a look at that data, and see what that can tell us.
19:53 Okay, so we're back in the pits now, and we've got our log file to look through.
19:58 Remember, what we're focusing on here is, looking at the response of the engine under medium to moderate load, and in the 1500 to 3000 RPM range.
20:11 When we go to wide open throttle, as we've already looked at when we did our full throttle ramp run, we're going to be running right out through the engines range, out to the rev limiter.
20:21 We've already looked at this area, we know that we've got good control over both our air/fuel ratio, and our ignition timing.
20:28 However, particularly for a street car, we're going to spend a lot more time down in the low to medium RPM range, and using moderate throttle.
20:38 So, this is what we're checking now.
20:39 What I've done is, I've used various throttle inputs, and I've also made gear changes while I've been testing, so I can see both the throttle response, as well as the response of the engine to these gear shifts.
20:54 While we're doing this on the road or track, we're also taking note of the feel of the engine.
20:59 So, is the engine responding crisply and smoothly to throttle input when we make abrupt throttle input changes? Or, is it bogging, or is it lagging? We're looking for that crisp response that lets us know that the transient response of the engine is good.
21:15 Now again, if we've done our job correctly, with our virtual VE and MAF scaling, this is what we should expect, but we always want to test this.
21:23 Let's have a look at our log file now and we'll see what we've got here.
21:27 Now, we can of course just move through the log file, and look at all of the data.
21:32 In particularly, at this point here, we can see that we do have some activity from our knock retard system.
21:39 However, if we're looking through the data in this way, it's quite difficult to really make much of an educated decision about what to do.
21:48 We can see that we do have the occasional amount of activity from our knock retard system.
21:54 It's important to understand, even when we test a completely stock standard car, we're always going to see some activity from the knock retard system.
22:04 In fact, it can actually be quite scary, just how much knock activity we're seeing in a 100% stock standard car.
22:12 This should be some guide to what the GM calibration engineers deem as acceptable.
22:18 If we try to achieve absolutely no activity from our knock control subsystem, what we're going to end up doing is actually hurting the engine's performance, because we're going to end up retarding the timing below what we really need to, and this is going to end up effecting the power and torque the engine makes.
22:38 Let's have a look at another way of analysing this data.
22:41 What we're going to do now is look at our spark retard histogram.
22:45 This is going to give us a better idea of the areas in engine operation that the engine is most prone to suffer from knock, or in fact where the knock retard subsystem, is doing some work.
22:58 We can see particularly here, in the 0.91 to 1.07 gramme per cylinder, and between approximately 2200 and about 2800 RPM, we do have some consistent knock activity occurring.
23:16 We're seeing in this case in particular, knock counts of two, three, and four, or knock retard values of two, three, and four degrees.
23:24 Which means, that knock retard system is doing a little bit of work.
23:27 Again, I'm not going to be trying to get this histogram to be completely filled with zeros.
23:33 If we're seeing consistent and repeated knock in one particular area of the engines operation, this is where we're going to be focusing our efforts.
23:42 So particularly, if I'm seeing values of two, three, or four degrees of knock retard, this is the area I'm going to be focusing my attention.
23:49 Again, just as we looked at on the Dyno, because we've set up our cylinder airmass, and our engine RPM axis to match our spark advance table, we can be very pinpoint accurate in where we're going to make those changes.
24:04 So the process from here would be to retard the timing in any areas that we're seeing consistent knock retard activity.
24:12 If we're making changes, we always want to make sure that we maintain a smooth shape to our spark advance table.
24:18 What this means is, if for example, in the area we can see here, we have four degrees of knock retard at 2200 RPM and 1.7 grammes per cylinder, I'm being inclined in this area to retard the timing around the surrounding cells by a degree as well, just to give it a smooth shape to our spark advance table.
24:41 Once we've made changes to the spark advance table, we can simply reflash the PCM with our new calibration, head back out onto the road, and confirm that our changes have had the desired effect.
24:53 Remembering of course, we're not looking for absolutely no activity from our knock retard system.
25:00 So, at this point our task of tuning the engine is complete.
25:03 We've tuned the engine initially on the Dyno, and then we've confirmed our results here on the racetrack under real world conditions.
25:10 We know that the ECU now has good control over the air/fuel ratio, as well as the ignition timing, under a variety of conditions.
25:19 We've checked idle, we've checked cruise, we've looked at wide open throttle, and we've also tested under transient conditions.