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Old 03-07-2020, 09:11 PM   #1
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Re: HP Tuners Tutorials - Idle Timing

Quote:
Originally Posted by neal64ss View Post
Seems normal as the PCM is monitoring and adjusting fuel/spark/throttle position in real time to maintain required RPM.
Yep, you are spot on, let's take a deeper dive and explore how these system intertwine.

Quote:
Originally Posted by neal64ss View Post
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.
Much appreciate the feedback.
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Old 03-07-2020, 09:29 PM   #2
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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
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Old 03-07-2020, 09:40 PM   #3
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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
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Old 03-07-2020, 09:41 PM   #4
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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.
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Old 03-07-2020, 09:58 PM   #5
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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.
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Last edited by Gregski; 03-24-2020 at 12:02 AM.
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Old 03-07-2020, 10:01 PM   #6
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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
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Old 03-08-2020, 11:15 AM   #7
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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.
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Old 03-08-2020, 12:06 PM   #8
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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!
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Last edited by Gregski; 03-08-2020 at 12:11 PM.
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Old 03-08-2020, 12:10 PM   #9
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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?
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Old 03-08-2020, 12:17 PM   #10
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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
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Last edited by Gregski; 03-09-2020 at 12:21 PM.
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Old 03-08-2020, 12:21 PM   #11
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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
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Old 03-08-2020, 12:27 PM   #12
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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
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Old 03-08-2020, 12:31 PM   #13
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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)
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Old 03-08-2020, 12:34 PM   #14
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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)
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Old 03-08-2020, 12:49 PM   #15
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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
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Old 03-08-2020, 12:56 PM   #16
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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
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Old 03-08-2020, 01:03 PM   #17
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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
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Old 03-08-2020, 01:06 PM   #18
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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
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Old 03-08-2020, 01:50 PM   #19
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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).
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Old 03-08-2020, 02:00 PM   #20
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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)
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Old 03-08-2020, 02:06 PM   #21
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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.
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Old 03-08-2020, 02:11 PM   #22
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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.
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Old 03-08-2020, 03:11 PM   #23
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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?
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Old 03-08-2020, 03:17 PM   #24
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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
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Old 03-08-2020, 03:25 PM   #25
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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.
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Last edited by Gregski; 03-09-2020 at 12:28 PM.
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