HP Tuners Tutorials

[Gregski]

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.

[Gregski]

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.

[Gregski]

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?

[Gregski]

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

[Gregski]

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.

[Gregski]

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.

[Gregski]

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

[Gregski]

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)

[Gregski]

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!

[Gregski]

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).

[Gregski]

Idle Tuning - Intake Manifold Absolute Pressure

here I am looking at my Intake Manifold Absolute Pressure reading of 37 kPa and it looks like it can be improved upon, more specifically we can try to increase my timing advance to see if this number will go down in kPa.

[Gregski]

now before we go any further please allow me to rant about Absolute Pressure since I had the hardest time switching from thinking in terms of vacuum to thinking in terms of pressure, one reason being that when I think of pressure I think of PSI as in I pump up my car tires to 35 PSI and off I go and not in Pascals, (I'm looking at you Blaise)

so if you are like me and are more confused than a blind goat on astro turf in terms of Pascals here's how I think of them

Imagine God is pushing down on your intake manifold, and the hardest she can push is 100 kPa or one atmosphere (technically that's how hard she's pushing on one square inch, but we're not even going to go there... ha ha)

so with your engine not running the pressure inside your intake manifold is equal to its surroundings. It's 100 kPa all around, on your truck seat, on your head, in the bed of your truck etc. that's just how hard the atmosphere is pressing down on us at all times, at sea level anyways.

so what happens when you start your engine, well in the old days thinking in terms of vacuum there was suction and perhaps we had 15 InHg read Inches of Mercury (Hg = Mercury, WTH?... "It comes from hydrargyrum, a Latinized form of the Greek word ὑδράργυρος" ah yes of course... Not! ha ha)

but now that all the Tuners think in Pressure not vacuum now what happens is...

At Idle - imagine when we fire up our engines a trap door opens underneath your intake manifold and now some of that 100 kPa being bushed down on the intake manifold falls down inside the engine, so we are essentially subtracting or taking away them Pascals so 100 kPa minus what ever fell through the trap door usually about 65 kPa or two thirds falls through... leaving us with only 35 kPa still in the intake at idle that is with the throttle blade almost all the way closed preventing more air from coming in

At WOT - now when we gun it and are in Wide Open Throttle WOT the throttle blade swings open allowing more of that air being pressed down on the intake manifold if you will to enter the intake, essentially returning the pressure inside it to almost nearly 100 kPa but not quite as the trap door is still open under it since the engine is running

confused? great! you're welcome

[Gregski]

Idle Tuning - In Park timing table

so at this point if we wanted to add more timing I wouldn't feel too comfortable guessing where to add it in the In Park table. We could willy nilly it and change all the cells that say 19 in the upper left hand corner and add 2 degrees to them making them all 21, but that would be stumbling in the dark, because all we know at this point is what RPM we are idling at but not where we land on the Y axis aka Cylinder Airmass, and we remember from our Timing discussion that GM likes to use RPM vs Cylinder Airmass to plot their timing curve.

[Gregski]

Idle Tuning - Cylinder Airmass

So this calls for adding yet another channel called Cylinder Airmass to our Attic, now before you all freak out and say Greg you told us this was going to be three things and here we have now added well over a dozen channels, allow me to explain.

Yes Idle Tuning focuses on three things, RPM, Timing, and Airflow, however in order to know what to tweak and why, we need supporting information ie additional Channels, but they are nothing new, we have covered them ahead of time in prior posts / write ups when we laid the foundation as this tutorial builds upon prior knowledge. Please see post #285 Also I already admitted I sometimes sprinkle in additional Channels (ie Mass Airflow, Dynamic Airflow) just for the sake of demonstration, so once you read through this once, you decide what Channels you will need to tune idle, kapish?

[Gregski]

Idle Tuning - Timing

So once again I went out and got us some data. Now we don't have to guess where to increase our idle timing at, now we can see that we are flowing .14 grams per cylinder while idling, from the Cylinder Airmass channel which gives us the X axis location that we were needing.

[Gregski]

Idle Tuning - Timing

Now I went ahead and also created a graph for those of you like me who are more visual types, this shows us exactly where on the In Park idle timing table we are landing on right now.

You don't have to go this far, this is sort of belt and suspenders solution, you could just rely on the Cylinder Airmass channel to pin point you to the right place on this timing table.

[Gregski]

Idle Tuning - Timing

here are the properties of that idle base timing graph just for completeness

[Gregski]

Idle Tuning - Base Timing

so just to regroup our goal is to keep adding Base Timing in the In Park table under Idle Spark Advance section in the VCM Editor until the Intake Manifold Absolute Pressure (kPa) stops decreasing, whilst keeping an eye on the Engine Coolant Temp, yes this is time consuming and yes you add 2° and have to write the changes to the PCM and then log some data and then add another 2° and log some more data, rinse lather repeat, [really makes you question that mail order PCM tune don't it? ha ha - sorry couldn't resist]

Here you see we bumped the timing from 19° to 21° and saw no change, the kPa was at 38 and stayed at 38, that's ok, let's keep going for a little bit more

Top Tip: we will take baby steps and add in 2° increments though you could bump it to say 25° and see if the pressure drops, if it don't you could save yourself some time knowing you were already at as low as it was gonna git

[Gregski]

Idle Tuning - Base Timing

notice on this next bump I expanded the highlighted area to the right to include the 800 RPM range, that's because the PCM uses the surrounding cells to average out the timing, and I wanted to be sure this time we were at 23°

hey lookie there, the kPa has budget, now keep in mind these numbers fluctuate so my initial was sometimes reading 37 and sometimes 38, so now that I see 37 that means we are moving in the right direction, and this could very well be a 36 sometimes as well, etc.

[Gregski]

Idle Tuning - Base Timing

OK, we are going to go one more notch and add another 2° for a total of 25° of Base Timing advance

And we see 36 kPa of pressure inside the intake manifold, however the coolant temp started to climb.

So that's how it's done, now on our stock engines these gains will be small so I would consider this fine tuning and it's really optional, but if you are seeing gains of 3 to 5 kPa then by all means tune that down as long as your engine stays cool.

Most importantly tune for how you want your truck to feel, how you want it to run and drive, and don't get too lost in the numbers, you don't want to get the perfect numbers and have it run hot and overheat, know what I mean, find that balance, you can always back off the timing advance even when you find the lowest manifold pressure. Turned out this engine did not like that much timing, it even got hot at 23° degrees so I backed it down to 21°.

[MDPotter]

Gregski, keep the posts coming. These are awesome. I'm getting dangerously close to ordering HPTuners.

I hate to say it, but I got a mail order tune in my truck right now. I've probably only put about 5 miles on it so far but I want to get into the PCM and see what's going on. It runs great, but I want to be able to see what the tuner did and to make sure nothing bad is happening. Are there some areas that I can check once I get in to see if I have a bad tune or if there are things I need to change right away?

I got the tune put on it as a base tune and they have a good rep, but I know it can never match tuning here where the truck is driven.

[Gregski]

Originally Posted by MDPotter

Gregski, keep the posts coming. These are awesome. I'm getting dangerously close to ordering HPTuners.

I hate to say it, but I got a mail order tune in my truck right now. I've probably only put about 5 miles on it so far but I want to get into the PCM and see what's going on. It runs great, but I want to be able to see what the tuner did and to make sure nothing bad is happening. Are there some areas that I can check once I get in to see if I have a bad tune or if there are things I need to change right away?

I got the tune put on it as a base tune and they have a good rep, but I know it can never match tuning here where the truck is driven.

Thanks and this is an excellent question, lets see if I can help you out, from having recently worked with someone in the same boat.

0. Are you throwing any codes. Did you wire up your MIL check engine light, is it on? You can read your codes with some cheap OBDII Code reader before you even buy HP Tuners so please check for any codes.

1. After you buy your HP Tuners the first thing you should do is simply read your mail order PCM to see if you got what you paid for, more specifically is it really the Year, Make and Model that you thought you were getting. This is important for a variety of reasons not just to see if your mail order shop was honest.

For example if you wanted a 2000 Camaro tune and got a 2001 tune back, things will not match. There are certain break point years where GM changed things: EGR to no EGR, cable vs drive by wire, returnless vs return style fuel rail, size of injectors, intake manifold design, etc.

2. In terms of performance I put Safety first, and by safety I mean engine safety, so check your Fuel Trims to see how lean your vehicle is currently running.

3. Engine Knock. If you are worried about engine knock, the easiest thing to do is to run high octane gasoline 91+ until you learn more about tuning.

4. Do a general stare and compare using the Compare feature in HP Tuners, I mentioned this feature earlier in my posts, but it's worth going over again. I doubt the mail order came with a stock tune file so you will have to now go and try to download one off of the HP Tuners website and hope somebody uploaded it there for you, this is yet another reason to roll your own, cause the first step is to save that precious unaltered tune file and never ever mess with it.

These are the high level points, I will dive deeper in the following posts to show how you can do this in detail.

[Gregski]

Right when you connect your laptop to your PCM for the first time and launch the VCM Editor and click the Read icon on the top menu, you will quickly be able to identify what vehicle your tune came from. Remember you can read your PCM inside the truck once it's all hooked up and you got your OBDII port wired up, or outside the truck if you built a bench harness with a little AC adapter to plug into the wall to read the PCM in the comfort of your own home (see Post #145).

Just because you sent in your 2000 Chevy Silverado PCM in doesn't mean you may get the same vehicle tune back, some shops do a PCM exchange some may over write your PCM with what ever vehicle tune they push so you may get a 2002 GMC Sierra tune back etc.

Once you read the file and saved it and forgot what year the tune came from for example, you don't have to read it again, just open the file using the VCM Editor and click on Edit \ Calibrate Details on the top menu and you will once again see the vehicle information you are looking for.

[Gregski]

Yes there is a dozen things to check once you fire up your rig for the first time but lets focus on things that will keep you from blowing up the engine.

So for this you want to connect your laptop with HP Tuners on it to your PCM, you can do this with your truck On or Off, running or not running it doesn't matter. Then open VCM Scanner on your laptop and just look at the left hand side of this super busy and cluttered screen, on the left you have something called Channels, (ignore the pretty graphs and charts on the right where your eye wants to wonder, ha ha)

look for four line items,

Short Term Fuel Trim Bank 1 (driver side)
Long Term Fuel Trim Bank 1 (driver side)
Short Term Fuel Trim Bank 2 (passenger side)
Long Term Fuel Trim Bank 2 (passenger side)

Not knowing anything about anything, and I am not putting no one down, here's what should be happening.

1. the numbers should be dancing, they should be changing, they all should be adjusting (while you drive around that is, and come to a stop sign or a stop light)

2. If you see any of the numbers stuck on 25 things aint good! Positive numbers mean you are running lean and the PCM is adding fuel, negative numbers mean you are running rich and the PCM is holding fuel back. Single digit numbers are ok +9 or -9 or less. Numbers of +4 or -4 are good, and numbers of +2 or -2 are awesome, but don't kill yourself trying to get those, as some days you will see them some days you will not.

Now keep in mind I am giving you some quick and dirty tips right here, in case some of you are reading this by just jumping onto this moving train, I would imagine that if you went out and bought HP Tuners you plan on doing things right and you bought yourself lots of beer and spent the hours needed to read this long sexy thread from the beginning so that you have some legs to stand on, kapish.

[MDPotter]

This is exactly what I was looking for Gregski, thank you! Once I get it purchased and hooked up I will let you know if I see any red flags.

I did wire up the OBD and plugged in a cheap scanner and didn't get any codes. I guess if a tuner was just plain evil they could disable all codes, but I have some faith in them.