Re: HP Tuners Tutorials - Idle Tuning
 

Idle Tuning

lets go back and consult our idle Base table to see what should be happening at 90° F

and sure enough, the Desired Idle RPM is 700 at 90° F in Park, the engine hasn't fully warmed up yet, I just jumped the gun, this happens to more people than you know

now I wasn't trying to trick you, or be a smart alleck, you must fully warm up your engine for it to settle in the specs it needs to settle in at

Re: HP Tuners Tutorials - Idle Tuning
 

Idle Tuning - Engine RPM vs Idle Desired RPM

It may have taken me 20 minutes for my truck to fully warm up to about 194° F where she likes to settle in, and that's ok, it would have happened faster if I was to drive her around the block, but I wanted just to log some pure data in Park

So here's what the numbers look like in Park when the engine is warmed up:

Engine RPM = 552
Idle Desried RPM = 550

pretty darn perfect

Re: HP Tuners Tutorials - Idle Tuning
 

Idle Tuning - Engine RPM vs Idle Desired RPM

now watch what happens when I shift her into Gear

Engine RPM = 525
Idle Desried RPM = 525

the Idle Desired RPM changed from 550 to 525 and the actual Engine RPM followed, as it should per the Base table, see how that works

Re: HP Tuners Tutorials - Idle Tuning
 

Idle Tuning - Chart vs Time

In order to further our RPM discussion it is time to get acquainted with a new feature of HP Tuners called Chart vs Time.

Re: HP Tuners Tutorials - Idle Tuning
 

Idle Tuning - Chart vs Time Layout

We add a Chart to our Layout in a similar fashion we have been adding the Histograms from the main Menu above

Layout \ Add to Layout \ Chart vs time

Re: HP Tuners Tutorials - Idle Tuning
 

Idle Tuning - Chart vs Time: Group

I start by nuking all the default Charts and start with a clean canvas. Then I first add something called Group this is just a break or a section to keep all the squigly lines (aka Series) separated and not stepping all over each other

Re: HP Tuners Tutorials - Idle Tuning
 

Idle Tuning - Chart vs Time: Series

once we have the Group we populate it with something called Series. Series are just visual line representations of the Channels we added already on the left hand side

Re: HP Tuners Tutorials - Idle Tuning
 

Idle Tuning

here are the Properties of the three Series I have added

Engine Coolant Temp
Engine RPM
Idle Desired RPM

Unlike the channels which are frozen once you log, you can make changes to the Series after the fact, so don't sweat it if you missed a check box or chose the wrong color or something like that.

Re: HP Tuners Tutorials - Idle Timing
 

Idle Timing

Time to take the kids for a haircut. But I leave you with this real Chart showing what my Idle Desired RPM is ie 550 and how my actual Engine RPM dances around it.

Why do you think that is?

Is this normal?

These questions are not rhetorical please chime in if you are following in real time.

Re: HP Tuners Tutorials - Idle Timing
 

Seems normal as the PCM is monitoring and adjusting fuel/spark/throttle position in real time to maintain required RPM.

BTW, I cant thank you enough for this thread. I have stumbled around for years without making any progress on my HP tuners (other than able to get stock engine to run stand alone). Suddenly with this thread I am starting to understand how it all works, and spending more time in the chevelle than I have in a long time.

Re: HP Tuners Tutorials - Idle Timing
 

Yep, you are spot on, let's take a deeper dive and explore how these system intertwine.

Much appreciate the feedback.

Re: HP Tuners Tutorials - Idle Tuning
 

Idle Tuning

Before we answer those questions, I wanted to show you what the Chart vs Time looks like as we shift from Park to Reverse to Neutral to Drive and back to Park. I held each phase for one minute so that we can see them properly defined. It may be difficult to see the actual RPM numbers in the graph, so I will just tell you that the Idle Desired RPM green line shifts from 550 to 525 to 550 to 525 and back to 500 just as the Base table dictates. Pretty cool

Re: HP Tuners Tutorials
 

Idle Tuning - Idle Spark Advance

And as Neal pointed out this behavior is perfectly normal the PCM is monitoring and making these adjustments, you will not see your idle RPM be a flat line at the desired number say 550, it will oscillate above and below it (within reason, more on this soon).

This brings us to the second item of the Holy Trinity: Timing. Let's open up the VCM Editor and see how the PCM uses Timing advance to keep the RPMs in line. We find the Idle Spark Advance under:

Engine \ Spark \ Advance tab \ Idle Spark Advance section

Re: HP Tuners Tutorials - Idle Timing
 

Idle Timing - Tables

Idle Timing is set by either of two tables depending what gear we are in

In Drive or In Park

So what we can gather from these tables, is that for example in Park (second table) in my case idling at 550 RPM my timing should be somewhere between (the 400 RPM column) 19° and (the 800 RPM column) 21° so obviously we can call that 20°. We are looking at the very top left hand corner of the table.

Note: These tables look very similar to the Base timing tables, ie High Octane and Low Octane ones, however note the column headings on the top, they go from 0 to only 4,800 (I guess that's high enough for idle, ha ha) but also note the break points, where is 600 RPM, where is 1,000 RPM? The point I am trying to make is that these tables do differ slightly, but it may be enough to trip you up if you try to reuse the Base timing Histograms we built earlier on, cause you get lazy or are not paying attention to detail.

Re: HP Tuners Tutorials
 

Idle Tuning - Timing Advance

Alright so back to the VCM Scaner we go to add some timing channels. First we add Timing Advance (the mother of all timing channels) this is the total of all timing advances and retards, it is as if we were holding a timing light to the crank pulley and reading the actual timing in real time.

Re: HP Tuners Tutorials - Idle Tuning
 

Idle Tuning - Base Advance

Now at this point just as with the RPMs we could write down what the In Drive and In Park tables say the timing should be, or we can once again work smarter not harder and use a special HP Tuners channel to do the work for us. We shall add such a channel next, it is called Base Advance

Re: HP Tuners Tutorials - Idle Tuning
 

Idle Tuning - Timing

I'm going to go log some more data for us to see what shows up in the two new timing channels we just added.

Just so you know you do not need to do it like this, you don't add the RPM channels and log data then add the timing channels and log more data, I am just doing this this gradually for demonstration purposes. This allows me to only show a few channels at a time so we don't get overwhelmed.

Re: HP Tuners Tutorials - Idle Tuning
 

Idle Tuning - Timing Advance

This time with the engine warmed up (somewhere's above 190° F) we have some timing numbers to look at. Here we see that the actual timing aka Timing Advance at this very precise point in time is 17° however it should be 20° according to the Base Advance that's 3° less than what it should be!

Re: HP Tuners Tutorials - Idle Tuning
 

Idle Tuning - Timing Advance

at a different point in time it's almost the opposite, now our actual timing Timing Advance is 24° where as the Base Timing (aka what it should be) is still at 20° that's 4° too much!

What is going on here, and why?

Re: HP Tuners Tutorials - Idle Tuning
 

Idle Tuning - Timing

let's take a quick look at the Timing Advance (white line) vs Base Timing using a Chart vs Time

ah yup, our timing (white line) is all over the place as compared to the green line of where it should be

Re: HP Tuners Tutorials - Idle Tuning
 

Idle Tuning

here are the Properties of the two series I used to make that comparison

FYI some of this stuff is me just going the extra mile to explain / demonstrate things, once you get the hang of it, you get to choose which weapons in HP Tuners you want to use to troubleshoot or tune, for now just muddle through it all please

Re: HP Tuners Tutorials - Idle Tuning
 

Idle Tuning - Idle Advance

let me share a very helpful channel that can help us make more sense of all this, it is called Idle Advance, and that name should really be Idle Advance Correction as it is not what the timing is at idle, but it is the difference between Timing Advance and Base Advance, ie the two channels we've been looking at so far, so it just does the math for us, win/win

Re: HP Tuners Tutorials - Idle Tuning
 

Idle Tuning - Idle Advance

alright so let's see that Idle Advance channel in action

note the numbers are a little bit off, but that's because I got rid of the decimal point and also there is a bit of a lag behind what the actual timing is and what HP Tuners reported, but it's close enough

again, the most important take away is that this Idle Advance parameter is the difference between the actual timing (Timing Advance) and what the timing should be (Base Advance) it is the PCM's attempt to make things right (how and why, coming up next)

Re: HP Tuners Tutorials - Idle Tuning
 

Idle Tuning - Idle Advance

something that i find useful and less cluttered is looking at this Idle Advance data by itself using a Chart vs Time like so

the scale is basically set to 10 and -10 degrees and I like for my timing to be within five, in this case the retard is fine it is well within 5° (bottom spikes) but the advance is too much (top spikes)

Re: HP Tuners Tutorials - Idle Tuning
 

Idle Tuning - Idle Adaptive Spark Controls

Ok, finally let's jump over to the VCM Editor and see what is causing this behavior. Lurking on the same tab as our In Drive and In Park idle timing tables are the Idle Adaptive Spark Controls

Engine \ Spark \ Advance tab \ Idle Adaptive Spark Controls section

more specifically the Overspeed and Underspeed tables

Re: HP Tuners Tutorials - Idle Tuning
 

Idle Tuning - Overspeed table

let's take a look at these tables one by one, starting with the Overspeed table first

at the top we have RPM, so for example when we go 50 revolutions over the desired RPM then according to this table the PCM will try to pull 5° of timing (hence the -5.0)

as you can see this table can pull us back from being as much as 300 RPM over budget (ha ha) by pulling 9° of timing, pretty cool, but I wouldn't set my timing willy nilly and depend on these "corrections" hope you follow

so I think of this table as Idle Retard Correction table, but you do you

Re: HP Tuners Tutorials - Idle Tuning
 

Idle Tuning - Underspeed table

now let's look at the fraternal twin, aka the Underspeed table

so the concept is basically reversed, but not directly proportional (in other words we don't add the same amount of degrees as we remove for being the same amount of RPMs off)

here if we are under by 50 revolutions we will actually add 10° of timing

again this table can reel us back from being 300 revs off by adding 14° so now that I think about it, we can add more timing than we pull (-10°) good to know I guess!

so I think of this table as Idle Advance Correction table, but you do you

Re: HP Tuners Tutorials - Idle Tuning
 

Idle Tuning - Overspeed & Underspeed tables

At this point I would not mess with these tables, I would just be happy knowing how and why my idle timing is changing, cause there's more to it...

we will cover Airflow next! and see how this Holy Trinity ties it all in together

Re: HP Tuners Tutorials - Idle Tuning
 

Idle Tuning - Airflow

So back to the VCM Scanner and it's time to add some more channels. We will be adding the following three channels:

Idle Desired Airflow
Idle Base PN Airflow
Idle Base Gear Airflow

the concept being the same as with the RPM and the Timing, the Idle Desired Airflow being what the engine needs to maintain our set RPM and the Idle Base timings are just reporting to what the hard coded values in Idle Airflow table are set to (we will look at that table next).

Re: HP Tuners Tutorials - Idle Tuning
 

Idle Tuning - Base Running Airflow

The Idle Airflow table can be found under

Engine \ Idle \ Airflow tab \ Base Running Airflow section

If we look at the bottom of the screen it reads: "This table is used to determine the base airflow (in g/sec) for the IAC/ETC control vs. Engine coolant temperature. This is used as a base setting (or startpoint) for the adaptive idle routines and also the base IAC position when the vehicle is moving."

Note the in grams per second part, I have actually changed mine to be in pounds per hour, it does not matter what units you tune in pounds or grams, as long as you are comparing apples to apples (just click the green g/s and it will toggle between the different units)

Re: HP Tuners Tutorials - Idle Tuning
 

Idle Tuning - Idle Airflow table

We should be getting the hang of reading these tables by now. You pretty much want to be in the green ie the operating temp zone. So if my engine likes to run at 194° F looking at the top of this table we would be somewhere between the 176° and 198° columns which is fine cause the values in those cells below are the same 43.7 in Gear and 42.1 in Park / Neutral.

Ok so in Park sitting in my driveway my engine fully warmed up should be flowing 42 pounds of air per hour, let's log some data and see what we actually are getting.

Re: HP Tuners Tutorials - Idle Tuning
 

Idle Tuning - Idle Airflow table

By the way when I do a first pass I am good with numbers before the decimal, so I may even get rid of the decimal to make things easy, it's only when you super duper need to geek out that you can add the decimals.

Re: HP Tuners Tutorials - Idle Tuning
 

Idle Tuning - Airflow: Idle Base PN Airflow

OK, so once again I went out and got us some data from a completely warmed up engine.

So here we see that according to the Idle Base PN Airflow channel we should be flowing 42 lb/hr (this number of course comes from the Idle Airflow table we discussed above) however our PCM is only asking for 40 lb/h as per the Idle Desired Airflow channel. So we are 2 pounds off?

Re: HP Tuners Tutorials - Idle Tuning
 

Idle Tuning - Airflow: Idle Base Gear Airflow

Similarly when I shift it into gear, our Idle Base Gear Airflow now says it should be flowing 44 pounds per hour, but the PCM now wants only 42 lb/hr as per the Idle Desired Airflow channel (you can confirm we shifted into gear because the Idle Desired RPM dropped to 525 RPM aka the correct number for in gear)

so somethings gotta be compensating for the difference, let's find out what it is

Re: HP Tuners Tutorials - Idle Tuning
 

Idle Tuning - Idle Fuel Trims

time once again to add more Channels, now don't let these throw you off they do not mean there is a fourth component to our Holy trinity, ha ha these are bundled into the Airflow third

by this time we've all heard of Fuel Trims, more specifically the Short Term Fuel Trims aka STFTs and the Long Term Fuel Trims aka LTFTs, but did you know there is a whole other set of Fuel Trims?

We have the Short Term Idle Trims which HP Tuners calls Idle Adapt (STIT) and for some reason they don't come separate for In Park and In Gear (oh well) and Long Term Idle Trims (LTITs) for both LTIT PN/ACoff and LTIT Gear/ACoff.

stay with me now, it's going to all fall into place shortly

So look at the LTIT PN/ACoff channel it is removing 2 lb/hr (so 42 Base PN minus 2 LTIT PN equals 40 Desired) there's our smoking gun!

Important Take Away: being only 1 lb/h off by either the Short or Long Term Fuel Trims is super awesome, if that's what you are seeing, go have a beer, you're done, ha ha. I am quite happy being 2 lb/h off for each one of those, but keep reading we are about to learn that up to 4 lb/h is still good.

Re: HP Tuners Tutorials - Idle Tuning
 

Idle Tuning - Short Term Idle Trims & Long Term Idle Trims working together.

Lets take a look at another example. Here we have shifted into gear and we should be getting 44 pounds per hour airflow per the Idle Base Gear Airflow channel. However our Idle Desired Airflow in order to keep the proper RPMs is only asking for 42.

So we look at the LTIT Gear/ACoff channel and it is only making a 1 pound per hour adjustment, hey that's not enough?! But wait, look at it's little helper the Idle Adapt (STIT) channel it is also making a 1 pound adjustment, for a total of 2 pounds. Remember the Short and Long Fuel Trims work together.

Re: HP Tuners Tutorials - Idle Tuning
 

Idle Tuning

alright to use a Baseball analogy, we have just rounded third base, but we are not done yet, so let's bring it all home!

Abbott & Costello Who's On First

Re: HP Tuners Tutorials - Idle Tuning
 

Idle Tuning - MAF & Dynamic Airflow

First let me offer you a top tip regarding airflow. Let's do a quick check to see if what's actually coming into our engine matches what's desired.

To do this let's add two channels that essentially do the same thing however using two different methods, aka tell us how much air is entering our motor. (we learned about these ahead of time, if you forgot, now may be a good time to scroll up.... a lot, ha ha)

Mass Aifrlow (SAE) (actual measured airflow by the MAF sensor)
Dynamic Airflow (calculated airflow using the MAP sensor)

Note I like to put them up on the top, I call that the Attic and I usually keep my Multipurpose Channels up here, they may differ depending on what exactly I am tuning ie MAF Calibration vs Idle Tuning, but I always have maybe up to six channels up here that I just always like to see (you roll your own)

Re: HP Tuners Tutorials - Idle Tuning
 

Idle Tuning - MAF & Dynamic Airflow

So once again I went out and got us some numbers. Now this is a bit of a tangent but the point I am trying to make is that your Mass Airflow, your Dynamic Airflow and your Idle Desired Airflow should all match. If they don't you got issues. At this time we are just doing this as a sanity check to avoid any glaring anomalies!

If there's a small difference of like 5 pounds or less then most likely your Idle Air Control IAC (valve, motor, thingmajig) needs to be calibrated (I may do a separate write up on that) as a general rule of thumb if desired airflow > dynamic airflow you will want to increase the IAC numbers in the IAC Steps vs. Effective Area table. If desired airflow < dynamic airflow you want to lower the numbers in that table.

If you are way off by like half then perhaps you or someone else decided to turn the throttle blade adjustment screw on your throttle body and your airflow is now way off. Just as a point of reference the throttle blade adjustment screw is screwed in from underneath up, with an allen wrench, as a starting point you should only see two threads peaking out the top of that screw hole, any more then that for a stock engine and you are opening up the throttle blade too much. Seldom is there a need to mess with this screw on a stock engine. And don't get me started on drilling holes in the throttle blade, LOL!

Re: HP Tuners Tutorials - Idle Tuning
 

Idle Tuning - Intake Manifold Absolute Pressure

Alright so now armed with all this information how do we tune our idle if indeed something is out of whack?

First of all on a stock engine we do not mess with the RPM setting, that has been determined by the GM engineers so our goal is to adjust the Timing and the Airflow to help maintain that RPM not to go around increasing or decreasing it. We leave that headache to the cammers ie the guys who installed a bigger cam, ha ha.

Again keep in mind this is with a stock engine, and when I say that, I mean stock drivetrain, so if any of you wise guys are like well my 5.3L is stock but I married it to a TH350, or strapped on some long tube headers with the O2 sensors a mile away from the engine... um no... that is not stock, ha ha.

So essentially the RPM ie the first part of the Holy Trinity is done, we just find out what we need to idle at based on the Base Setpoint table and we accept it.

This leaves us with Timing and Airflow. Let's start off by trying to dial in our timing. So lets assume we are just like 2 pounds off on our airflow, (so essentially we are good, or good enough, we don't see anything way off) so what I would do here is adjust the timing by increasing it until I found the highest vacuum or as the cool kids say these days lowest Intake Manifold Absolute Pressure.

So let's give that a go. First we need to add yet another channel, again this one goes up in the Attic, and it is called Intake Manifold Absolute Pressure read in kPa you are looking for the lowest number (low 30s would be awesome).