Summary

One of the areas we see a lot of people struggle with when reflashing GM vehicles is with the idle performance. This is particularly an issue if you’re planning to fit a large cam. We’ve seen many tuners use work arounds such as drilling holes through the throttle butterfly but in this webinar we’ll show you how to address the tuning correctly all within the software.

Transcript

- Hey guys, Andre from High Performance Academy. welcome to another one of our webinars where today we're going to be talking about idle tuning in GM vehicles using the HP Tuners software. Of course if you are tuning GM vehicles on another platform, everything we're going to talk about today will also port across quite nicely. Of course the tables and the setup may look a little bit different. So I think it's probably worth starting by talking about what considerations or what factors we need to take into account when we are tuning idle speed and why it's such a problem in the first place.

And I think why it's a problem in the first place is a good place to start there. This is an area that I see a lot of tuners really struggle with, particularly with modified LS V8s. When we start adding a cam in particular, this can play havoc with the factory calibration and it's most noticeable in the idle areas of the map. So it's not uncommon for someone to fit a large aggressive cam, they'll get the rest of the tune dialled in really nicely, the cam's given them a huge improvement in power and torque at higher RPM but by virtue of the larger more aggressive cam with a lot more overlap, a lot more lift and duration, we end up significantly reducing the volumetric efficiency of the engine down in the low RPM regions and this really makes it hard to get the engine to idle. And if you're talking about a daily driven vehicle here, this is one of my pet hates.

I really hate a car that needs to be nursed by the driver in order to idle properly. Particularly when it's cold or maybe when you're coming up to a set of traffic lights, you'll be coming to a stop, there's nothing worse than your car stalling on you. So for me, regardless whether I'm tuning GM vehicles or I'm using an aftermarket standalone ECU, I generally put a lot of effort into my idle tuning in order to try and replicate as well as I can, the sort of quality we can expect with a factory car. So what I'm talking about here is a car that regardless whether it's stone cold or up to operating temperature, whether you're in the middle of winter with sub zero temperatures and snow and ice, or it's scorching hot in the middle of summer, I want to be able to reach in through the door, turn the key, not touch the throttle pedal and have the engine start and idle at a sensible RPM and then continue while it's warming up. I also want to obviously be able to drive the car around without any danger of it stalling.

So this is what we're trying to get. Now I've also sort of touched on in that discussion there why it can be a problem. We've talked about the reduction in low RPM volumetric efficiency of that large cam. So when we are tuning a factory LS engine, generally if we're reflashing it, the idle speed tuning is something that we don't need to give too much consideration with. Provided that we have a relatively standard engine internally or a standard engine internally I really should say there, we're not going to need to manipulate the idle parameters too much provided we've got our mass air flow sensor calibration correct.

Or if you're running a speed density patch, that you've got your VE table dialled in. It's really only when we start making more serious modifications that these problems start to come up. So we're going to dive in and have a look at some of the tables that you're going to need to adjust, we've got a setup going here on our scanner that I'm going to talk you through and we'll have a bit of a demonstration of that. As usual, if you've got any questions, please ask those in the chat and we'll deal with those at the end. And I'll just mention this probably is going to be a little bit shorter in terms of our usual webinars so if you do have any questions, please feel free to jump in quickly with those so that I don't miss out on those.

Now with tuning our fuel and ignition, one of the first places we need to start, sorry with tuning our idle speed control one of the first places we need to start is by getting our fuel and our ignition tables correct. This is something I see quite often both on reflashing packages as well as standalones is where an engine won't idle properly and the tuner is trying to fix those problems with the idle speed parameters. But the actual problem is that the fuelling is way too lean and the engine's just not happy idling at a very lean air fuel ratio. Or exactly the same situation can happen if the fuelling's way too rich or you've got large steps in your ignition table that are causing problems. So you want to really start with the basics and make sure that you've got your VE table dialled in or your mass air flow sensor calibrated correctly and make sure that you've got sensible numbers in your ignition table.

The other aspect that we need to factor in here is that when we modify a factory engine, factory LS engine and we fit a large agressive cam. We need to consider what RPM that particular engine is now going to want to idle at. And with a stock LS, we may find that the factory idle speed's somewhere in the region of 550 to 600 RPM and it'll idle quite happily there. If we've got a really big aggressive cam with a lot of duration and overlap, you're going to really struggle to get that cam to idle happily at such a low RPM. So that's another thing we need to factor in, we need to make sure that our target idle speed is sensible.

And this will depend on the size of your cam, the lift and duration. But particularly for a decent size cam where we're up in the 240 degree, 50 thou duration sort of area, we're probably going to need to settle on an idle speed maybe somewhere up around 800, 850 RPM. Obviously as your cam becomes more mild we can drop closer to our target idle speed. So that's really the setup that we need to start with to make sure that we're actually asking for something that the engine is going to be able to achieve. If we aren't sensible with those numbers, we're just going to be wasting our time trying to get the engine to do something that it's just not comfortable doing.

This does bring in a little bit of trouble when we're dealing with an automatic transmission if we've got a factory torque converter in the transmission. The reason for this is the factory torque converter is obviously designed for the factory cam, the factory idle speed. It's quite a tight converter, so we do get to a situation with a large cam where we need to bump up that idle speed. Particularly when the car is in drive, if we take our foot off the brake, the car can tend to be quite pushy, can tend to drive forward. So do need to be mindful of that.

There really is no workaround there, we do need enough idle speed to make the engine idle happily. If you aren't comfortable with an automatic transmission with a tight converter like that that's pushing a little bit, then the option there is to look at a modified high stall converter that's better suited to a really aggressive cam. Alright so what we'll do is we'll head across to the laptop screen for a moment. And I just want to take you through a couple of the tables that we need to adjust here. So what we'll do is we'll head over to our idle tab.

Obviously that's where we're going to be doing a lot of our tuning here. And for a start we've got our RPM, we've got RPM and air flow on top of these tabs here so we'll start on our RPM. And what we're going to be doing here is starting with our base set point. So we'll click on that. And what we've got here is just a simple three dimensional table relative to engine coolant temperature and for an automatic transmission whether we're in a gear or whether we're in park or neutral.

And these are just our idle targets. So we can see that down when the engine is cold, we're targeting about 850 RPM idle and this progressively comes down to the point where once we're above 80 degrees C, we're targeting 550 RPM. In this case that table is the same regardless whether we are in gear or we're in neutral. So again, first place to start. And what I would do if you've got a large cam, I've already talked about the fact that in the normal operating area where, up around somewhere here, where we might need to be maybe 750 to 850 RPM, I would also in that instance bump up our colder areas, maybe we don't need to add the same sort of 300 RPM to that but 850 I might take it up to 950 or something of that nature because the cammed engine is also going to struggle to idle when it's cold too.

Alright so once we've got our base idle set point set up, we can come across to our idle air flow tab, so we'll click on that. And there are a couple of parameters that we're going to need to mention here. So first of all we have this parameter here which is for our effective area, which is for our electronic throttle control and it says percentage max. Now this is an area where there's a lot of debate and a lot of confusion in the tuning industry for those who even are quite familiar with tuning GM vehicles. And while you don't need to touch this number when you're dealing with a stock engine with a stock cam, what you will find is that when you are tuning an engine with a large cam, particularly when it's cold, the engine won't idle properly.

No matter what you do, without changing that parameter you won't be able to get enough air bypass through the throttle body in order to get the engine to idle when it's cold. And what you'll probably find, I forget the exact number now, but what you'll probably find if you look at what's happening in the scanner, you'll find that the throttle position, I think it taps out at either 24% or 27%. And it'll just flatline there no matter what you do with the next tables we're going to look at. And this is because of this parameter here, our percentage max. So in a stock calibration we'll find that that's just a little bit below 2%.

And this limits the maximum amount of throttle opening we can use. A lot of tuners have resorted to drilling holes through the throttle plate in order to bypass more air through the throttle when it's closed, this is ugly, we don't need to do that. Also it can present some other problems which come up further down the line. So it actually creates often more problems than it fixes. So the solution here is to instead deal with our percentage max value here.

1.9% in stock form, what you're going to need there is going to depend on the size of your cam. With a really aggressive cam, we could end up, up around about 4% and that's just going to allow a larger range of throttle opening in order to bypass more air through. We can get our engine idling nicely, we don't need to pull out a drill and drill ugly holes through that throttle butterfly. So this is something we just need to look at, what's actually happening in our scanner, as I've mentioned, it is an issue that you're going to have mostly when the engine is stone cold and you start it. So you want to scan and look at what your throttle position is doing and if your throttle position is flatlined, as I said, around 24% to 27% off the top of my head, then you're going to need to increase that percentage.

Likewise if you can increase it from 1.9 to let's say 2.5, it'll allow a little bit more opening, if you still can't get that idle speed correct when it's cold, and you're still seeing that throttle flatline, then you're going to need to increase it a little bit further. So treat it with a little bit of care because this does affect essentially the resolution of the idle control circuit as well. So we don't want to just go and slam in 10% or 15% there, that's not going to be a smart way to deal with this. We want just enough to get our engine idling when it's cold and not necessarily any more. The next table that we are going to be needing to do some work in is our base running airflow table.

This will look a little bit different depending on what engine control module you are dealing with here. But here we have air flow final minimum. This is set up a little bit interestingly because it is relative to our idle air flow RPM, so basically our idle target and we've got a table that's three dimensional relative to our gear that we're in. What this essentially does, you can call it a feed ** table for the idle control circuit which of course uses in this engine a drive by wire throttle body. So basically this is telling the engine control module what air flow it's predicting it's going to need for idle and this will set the particular throttle position that it's going to use.

So again in stock form, not a lot of need to make changes to this table. When we've got a modified larger cam in the engine, we're going to need a lot more airflow. So particularly down in the sort of 600 to 1000 RPM area, we're going to need to pick those numbers up quite significantly. And just to get our engine to start initially, you may need to add as much as 50% to these values, maybe even more. But I'd start by doing that before we move into the next step which is where we are going to use the scanner to help us dial in those numbers.

So this is another good point to mention, if you've got any questions, please ask those and we'll deal with those in a second. I did mention that the tables are going to look a little bit different depending on what particular vehicle you're working with, what engine control module you're working with. I'll just show you another version from a gen 3 LS1, so we'll just open that up. If we can. And again we'll go to our idle airflow tab, we've got our base running airflow.

So essentially the same thing, this time if we click on that tab, we can see that now we've got our base running airflow relative to gear and relative to our engine coolant temperature. So we've got this three dimensional table. And this is where we can use our histogram in our VCM scanner to really help us fill in that table and get it right. So how that works is we're going to set up a histogram the same break points as this table. I'm not too worried about gear, whether we're in gear or park and neutral, and then we're going to use that histogram to fill in that table.

So let's just have a quick look at that now. So I've got the idle air flow histogram that I've just created, I've got that here. I have only made this two dimensions because we can't basically fill this in, the complete table in in one go anyway. So we'll just quickly have a look at how I've set that up. So if we go to our graphs layout.

We'll go down to our idle air flow histogram which is down the bottom and we can see that the parameter that we're logging into this is our mass air flow. So it's called idle air flow, basically we're just looking at the mass or air entering the engine or what mass of air in grams per second the engine needs in order to idle. If you are more comfortable working in imperial units, of course you can select this to be in pounds per hour, pounds per minute, whatever you want, doesn't really matter, the principles are still the same. Then we are replicating the table that I just showed you back in our editor, I'll just pop over again. So we know that we've got our engine coolant temperature on the horizontal axis.

Go across to our scanner, that's what I've selected here, click on the parameter and you can choose any parameter, we've got our engine coolant temp sensor. And then I have copied and pasted the numbers from the table. So again just to show you how that works, if we go back to our editor. If we right click in our table, and we go down to column axes, because it's the column axes break points that we want to use. And we click copy labels, we can come back across to our scanner, I've already got these entered here so let's just get rid of them for the moment.

And we can control V, that'll copy those in and it will create the histogram. So the idea here is once we've gone through our initial setup and we've got the engine to a point where our fuelling around the idle areas is OK, our ignition at the idle area is OK, we've actually got the engine to a point where the base running airflow tables may not be correct, they may not be optimal, but we've at least got the engine to a point where it will run quite well. So what we can then do, and we'll just start our engine up here. And what we want to do is just, we'd want to do this from stone cold ideally and as soon as we've got the, that's perfect, just what I wanted. We'll try opening our scanner again.

Don't quite know why that decided to quit on me. But what we want to do is then start filling the histogram with data, so we'll just get back to that. No wrong one. Nothing ever goes right when you're trying to do these live. But I think we do pretty well most of the time, no, OK let's just create that histogram again.

We will add a table, this is going to be a good opportunity to see how that works anyway. So what we're going to do is start by choosing our parameter that we're going to log into this and of course that is our mass air flow. So we're going to double click on that and that is now our mass air flow in grams per second. We're going to select our column axes which is our engine coolant temp. Double click on that, and that has added that in.

And hopefully we should still have the break points added, we do. And we can give this table a name, so let's call it idle airflow. Hopefully now we should be good. I should have saved that originally, I wouldn't have had that problem. Alright so we'll go down to our idle air flow table and we're going to start our histogram up.

Now this engine isn't stone cold so it's not going to be a perfect example here. So you can see that we're really starting already from 56 degrees centigrade. So we're going to be normally starting it from stone cold first thing in the morning and we're going to hopefully be able to capture data in the middle of winter here in Queenstown, probably down from pretty close to zero degrees. And we're just going to allow the engine to warm up to the point where the fan's kicked in, so we're probably going to end up somewhere up around about 100 degrees. And as the histogram fills in more data it's going to average these values and it's going to give us a really good set of data that then we're going to be able to copy out of this histogram and we're going to be able to dump it straight back into our base running airflow table.

Now of course that's probably going to give us data here from maybe eight degrees through to 100 degrees or something of that nature. We can use a little bit of common sense here and extrapolate the sort of shape we're seeing so that the areas both below as well as the areas above in this table still follow that same trend. And they're going to be at least there or thereabouts if we do happen to be operating in an area we can't get to. Now in this instance you can see that the numbers in this table are different depending on whether we're in gear or whether we're in park and neutral. A lot of people will just take the values from letting that histogram run its course in park or neutral and then add one or two numbers to the table which you can kind of see is exactly what we've got with these numbers already.

Or alternatively if you want to be a little bit more particular, you can run that histogram twice, do your first test with the car in park, then the next day when it's stone cold again you can re run that test with the car in gear. And you're going to be able to fill in that table correctly. Now I will mention that while the histogram should give us pretty good results here, I've generally found that it's a good idea to paste the numbers from the histogram in and generally you're still going to probably get the best results by increasing them by about one or two grams per second. The reason for this is that if you just put the numbers from the histogram in you're going to find that you will tend to get a little bit of a drop in RPM as you come back to idle. So by increasing those, bumping them up just one or two grams per second, you'll tend to find that it will hold that idle and won't drop down below your target so it'd just drop down to that idle speed a little bit nicer.

Alright so that's a quick and easy way of going through and tuning your base running airflow tables. We've talked about that parameter with the drive by wire vehicles that's going to allow you to get a little bit more throttle opening when the engine is cold. The other thing that is worth mentioning here, I'll just go back to my other calibration. The other thing that's worth mentioning here is we do also have adaptive idle control. So that can help with controlling the idle speed by using the ignition timing.

So basically if we come back across to my laptop screen, just close this down for a second, we are on our spark table here and we are on the advanced tab. And then we are looking at our idle adaptive spark control which are these parameters here. So we can see that we've got selections for over speed and underspeed, pretty sensible, if it's overspeed, it's above our RPM target, if it's underspeed it's below our RPM target. We've got our values for park and neutral as well as in gear. And essentially the parameters here, the axes that we've got is the error in RPM from our idle target.

So we can see that when we're on our idle target, our spark adder is zero so we're just using our base spark table value. And then progressively as our error increases and we get further and further above our idle speed, we can see that the spark advance is removed. And if we open up our underspeed table we're going to see exactly the opposite. As our idle speed drops below our target, we start adding spark advance. So a couple of aspects that we do need to be aware of with these tables.

These are obviously tables that will work well with a stock engine. Generally because an aggressive cam tends to be a little bit more lopey than a stock cam anyway, I find that the stock adapter spark tables can be a little bit overbearing, a little bit too aggressive. So sometimes dialling these down can help your idle quality. A good way of doing this is just to highlight the entire table and you can start by multiplying by half, so let's just have a look at how we'd do that. We can click on the top left to highlight the entire table, 0.5 and multiply.

And if we do that for both our underspeed and our overspeed, this will tend to just dull down the effect of that adaptive idle a little bit and can make the idle quality a little bit better. Same with our overspeed there as well, but basically with these parameters, it's just a case of testing to find out what your engine responds best to. Last thing I'm going to talk about here before we jump into our questions is that particularly with an aggressive cam, while this isn't really related to the idle tuning specifically, what we can also notice is that just off idle, at very light throttle where we're just pulling away from a stop, the cam can become a little bit lopey and make the car a little bit hard to drive smoothly. This is more noticeable in a manual transmission than an auto. The torque converter tends to damp down some of that loping in an automatic transmission.

But while it kind of goes against our normal tuning process, we can actually improve that situation albeit not fix it completely, by retarding the base spark advance values in that area of the table. So what we're doing there is purposefully retarding the spark values from MBT so this reduces the engine torque which in turn just reduces the effect of that loping so a few little tips for you there. Alright we'll jump into our questions and see what we've got. Supersayianjim has asked, so a 264 cam should idle at 1000 RPM? OK so what you need to know is a lot more about the cam. So what we need to know is the duration, so you've mentioned 264 there, I'm not sure if you're talking about duration of 264, that would be a pretty wild cam, or that's a specification, or part number or listing for a cam.

So it's the duration of the cam that's important. But also the lobe separation angle is important as well as where you've got that cam dialled in. So it's not, you'll probably find that your cam manufacturer is going to be able to give you a pretty good idea of what a likely idle target is going to be to suit that particular cam. ModMotorMayhem has asked, is this only to do with electronic throttle? No it isn't. So the gen 3 tables that we just looked at before, the base running airflow for those works in a slightly different way because it's got an idle air bypass solenoid.

But that base running airflow is still a parameter that's relevant for those. These days I don't do a lot of the older gen 3 stuff with cable throttle. Most of the stuff we're seeing these days is drive by wire so that's basically been my focus for as long as I can just about remember now. THATC0RPSE has asked, my LSX454 stumbles and stalls when the ambient temperature gets hot, generally about 90 fahrenheit or higher. It rarely, if ever, stalls below that temperature.

The car has a manual transmission in it and the idle is set to 850. It does lope at idle but that's expected, I have it set at 13.8 air fuel ratio at idle. It has a cable operated throttle body, it doesn't stall or die when I'm tuning in the driveway, only when driving and slowing down to a stop. OK on face value I'm not too sure I'm going to be able to give you a good pointer on that right now. I'd probably like to see a calibration from that to see exactly what's going on there and hopefully that would shine some light on what's going on.

Particularly a calibration coupled with a log file of when that stalling is occurring would be the perfect scenario so we can see exactly what's going on. I will just mention something there about your idle air fuel ratio. So this again comes down to the aggressiveness of a cam. What we do need to understand is that with a large cam with a lot of overlap, we may find that our air fuel ratio measured by a wideband in the exhaust is not actually that accurate. So this really is a case of testing to see what your engine actually responds to.

But 13.8:1 for a large cam with a lot of overlap is probably actually quite rich. And you'll notice this particularly if you find that if you've got the engine idling in a confined space and you start finding that your eyes are crying because of the fumes, that's probably a pretty good sign that you're actually probably still a little bit rich. I'll give you an example, while this isn't LS based, one of our race cars which runs a very aggressive cam profile, we were actually targeting a air fuel ratio of about 15.5 at idle. Now that might sound ridiculous but it's not a case of actually achieving 15.6 air fuel ratio in the combustion chamber, it's just because we're getting a lot of reversion pulsing, we're getting unburned oxygen passing through the system and it's not giving us a true representation of the actual air fuel ratio the engine's running at. So what I do there is just test at various air fuel ratios and just see how that affects the engine's idle speed.

If we've got our adaptive idle turned off, as basically the air fuel ratio gets to a point where the engine is happier running, you're going to find that the idle RPM will tend to pick up. At the same time, you'll generally tend to see the manifold pressure drop away. So those are a couple of guidelines to see where a heavily cammed engine may actually want to idle. So just a further reference to that, if you are a HPA member, please feel free to post up that information in the forum and I'll be happy to try and help you out in a little bit more detail there. Just probably missing a few of the details I probably need to really be able to do justice to that answer here in our webinar.

AutoWorkx has asked, is cold starting on E85 always tricky, would you be more likely to pull fuel or add fuel? Yeah it is always tricky unfortunately, particularly if you are working in colder climates. The problem with E85 is the fuel is harder to vaporise, it doesn't vaporise as easily as normal pump gas and this becomes more of an issue at colder temperatures. This is why you see in a lot of the areas of the world where they have E85 at the pump, they'll have a winter blend and a summer blend. I can't remember off the top of my head but I think in winter they're legally allowed to go down to about 55% or 60% ethanol so quite a big swing that you will see. However, getting a little bit off topic there, with E85, particularly if you've come from a gasoline tune, one of the areas that needs more work than others is that you'll need more cranking fuel enrichment.

So generally with warm up enrichment and the fuelling in general, you need to add fuel. But you tend to need more proportionally in the cranking enrichment to get the car started initially. Raze the Roof has asked, if it's already at MBT when idling, how does adding timing make it increase in speed when there's an underspeed condition? That is an excellent point there and the answer is it can't. And that's why we purposefully detune our idle spark advance from MBT. We want to make sure that we've got some head room to both advance the ignition timing and gain torque as well as retard the ignition timing and reduce torque.

So yeah absolutely right, if you're at MBT, you've only got one way to go and that's not going to be too helpful with an adaptive idle ignition strategy. Right that brings us to the end of our webinar and hopefully everyone now has a little bit more insight into GM idle tuning. As usual for our members if you've got other questions that crop up, please ask those in the forum and I'll be happy to answer them there. Thanks for joining us and we'll look forward to seeing you next time. For those who are watching on YouTube today, this is just a little insight into what we put on for our HPA gold members every week.

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