HP Tuners Tutorials

[Gregski]

Timing

GM sets timing in the Gen 3 engines in two places relying on four different tables.

1. Idle Spark Advance section (In Drive table or In Park table)

2. Base section (High Octane table and or Low Octane table)

All four of these tables live under Engine \ Spark \ Advance in your VCM Editor

We will start out by talking about the Base ignition timing ie the main timing.

[Gregski]

Timing

First the High Octane & Low Octane table names to me are a bit of a misnomer, I look at them as Aggressive Timing table and Moderate Timing table. The PCM does not sense octane levels in our fuel, it uses something called the Knock Learn Factor to determine which timing table to depend on or a combination of the two. We will cover Knock Learn Factor later on.

GM considers 93 Octane to be High Octane. Well I live in Northern California and I can't seem to find 93 Octane at the pump, so what table am I using?

The PCM wants to run off of the High Octane table however it is capable of averaging out between the two tables when it senses knock so your timing may not precisely match the High Octane table nor the Low Octane table at any given time, and that's ok. Also if you put in cheap gas you may find yourself running off of the Low Octane table exclusively and even then may still have some knock.

We will address all that, but first we take a peak at these two tables. Please note the differences at the higher load (larger Cylinder Airmass numbers) and RPM levels aka bottom right hand corners of the tables, ha ha.

[Gregski]

Timing

Let's take a closer look at one of these tables (it don't matter which one at this point in time)

The X axis ie the title on top Engine Speed (rpm) is self explanatory. However please look at the Y axis label on the left hand side Cylinder Airmass (g).

Unlike other manufacturers who use RPM vs Load (aka Vacuum / Manifold Absolute Pressure) for their timing tables, GM uses Cylinder Airmass (g). It is important for us to acknowledge this for various reasons.

1. The stock Histograms / graphs that come out of the box from HP Tuners are useless for us in terms of tuning or troubleshooting. They will all need to be modified / corrected to reference this Cylinder Airmass parameter instead of Manifold Absolute Pressure.

2. Cylinder Airmass is a calculation that takes the MAF input as well as the VE Table input into account. This is why we calibrate the MAF and the VE Table first. If the MAF / VE Table are off, than the wrong timing will be applied to your engine as it is based on this very important Cylinder Airmass (g) computation, and you will be left chasing your tail.

And yes just as with the VE Table the timing tables can also be viewed as a three dimensional graph.

[Gregski]

Timing

Example: Let's assume at 2,200 RPM the PCM calculates the Cylinder Airmass as 0.44 grams, according to this table that calls for 29* of timing advance. However the MAF and or the VE Table were not calibrated and are off, so the actual Cylinder Airmass should be 0.48 grams, now the correct timing should be 26* degrees. That's three degrees off, it could mean the difference between a smooth running engine or engine knock occurring. In higher RPM ranges under higher load, such a discrepancy can easily rob you of some power, and this was only a difference of one cell, imaging being two or three cells off.

[Gregski]

Timing

At this point let's jump to the VCM Scanner and setup a Histogram / graph to show us what exactly our egnine's timing looks like.

We only need three Channels to get started:

1. Timing Advance (this will give us the meat and potatoes aka the values in the cells)

2. Engine RPM (this will be our X axis ie the Title on the top of the graph just like in the High (or Low) Octane table)

3. Cylinder Airmass (this will be our Y axis label, again just like that of the Hight Octane (or Low Octane) table)

[Gregski]

Timing

Next we build our Histogram aka graph to match the High and Low Octane timing tables

[Gregski]

Timing

Lets take a close look at the Properties of our Timing Advance graph

Label: call it what ever you like, such as: Timing Advance

Parameter: although we select Timing Advance this silly program changes the name to Spark Advance on this screen

Decimals: I start with 0 you can get more granular later

Filtering
Function: this is important but it's a bit more of an advance feature which we will touch on later (you could use it to exclude things above your idle RPM say anything above 550 or Throttle Position greater than .5)

High Value: 50 cause that's the highest thing in my High Octane table (though this can be exceeded)

Low Value: -15

Column Axis
Parameter: Engine Speed aka Engine RPM

Values: copy the Column Axis labels from the High RPM table in the VCM Editor

Row Axis
Parameter: Cylinder Airmass

Values: copy the Row Axis labels from the High RPM table in the VCM Editor

[Gregski]

Timing

So after you have your Channels and your Graph all setup, you can go for a test drive and record/log some data. You do not need to write/Flash anything from the VCM Editor to do this.

Here is a look at some of my numbers.

I highlighted a cell at 1400 RPM and 0.28 grams with a value of 26 degrees advance to show you that it does not match either of my High Octane or Low Octane Tables. You may find yourself in a similar situation. So what gives?

So far this is what I wanted you to discover.

1. Where your timing settings come from (High and Low Octane tables), aka what they should be.

2. And what they actually are, aka the new Histogram / graph we just populated with data.

So we may not have all the answers but we at least now realize that there may be a discrepancy.

[Gregski]

Timing

To answer our question of why our actual Timing Advance does not match our Base timing, we must explore what we call Modifiers, ie there are additional tables that alter the Base table values, based on some condition.

Let's meet these dirty rascals:

Lurking on the same tab as our Base tables under Engine \ Spark \ Advance tab Base Corrections section we start with:

• Fuel aka AFR
• IAT
• ECT
• EGR
• Catalyst Heating

all eager to mess with our Base timing, ha ha

[Gregski]

Timing

Those of you who followed along from the beginning, you most likely turned off the EGR (Part IV) and the Catalyst Heating (Part VIII) as instructed in the Housekeeping section. Now we began to see why that may have been a good idea, especially on an engine swap where those components have been deleted.

Let's add some more Channels to monitor these Base Corrections to see if any are actually kicking in and altering our Base timing.

We will leave the Cranking Advance and Idle Advance for later when we tackle Idle tuning.

Note: In addition to these five Base Corrections, Torque Management is the biggest power thief when not tuned properly. This is also worthy of it's own Section / discussion.

[Gregski]

Timing

After you have added more timing Channels you can go for another test drive and record/log some more data. You do not need to write/Flash anything from the VCM Editor to do this.

You also don't need to pre build the additional Histograms / graphs at this time, as long as you are capturing the additional Channels, you can make the graphs later.

[Gregski]

Timing

After your second test drive, you can replay the log on the computer in the comfort of your own home, and just look at the values next to these additional five channels to see if any of them are making any changes to our base timing:

• Fuel / AFR
• IAT
• ECT
• EGR
• Catalyst Heating

And or you can clone the Timing Advance graph for each one of these to Geek out even more. It is a bit more work but it will show you exactly precisely where the timing is being altered.

Let's clone/copy one graph together. Let's make a graph for ECT Advance (which again in the graph wizard HP Tuners calls Coolant Advance)

All we have to do is change the following:

Label: Coolant Advance

Parameter: Coolant Advance

View: over on the right hand side we can choose how to show our data the default being Average but if you want to scare yourself a bit especially when it comes to engine knock change that pull down to Max, ha ha

and we are done and ready to see the results on our newly cloned graph

[Gregski]

Timing

Alright so I went out and drove around for about 8 minutes and got us some sample data. Using our basic timing channels here we can see that indeed the PCM is pulling out a tiny bit of timing based on the Engine Coolant Temp ECT as per the Collant Advance channel.

Now what's the point of this exercise? It is simply to make us aware of the things that the PCM may be influenced by to alter our base timing. It is not for us to go out and 0 out all these tables, leave them alone. The PCM is doing what it is designed to do, essentially protect the engine, from overheating for example.

This is different than zeroing out tables for the EGR and the CATs because those components no longer exist. If you are seeing numbers for your EGR Advance below, yet you have deleted it, you may want to revisit Section IV under Housekeeping.

[Gregski]

Timing - Knock Parameters / Channels

No discussion of timing would be complete without the subject of knock, (engine knock also commonly known as pinging) or more specifically Knock Retard.

Engine knock is caused by the piston still coming up in the cylinder and the spark igniting too soon forcing it down before the piston had the chance to reach top dead center and began its decent downwords.

Have you ever pushed a friend or a sibling on a swing and and stood too close and had the swing slam into you, well you experienced something very similar to engine knock, had you stood further back the swing would have reached the end of the pendulum (equivalent of TDC for a piston) and began to swing back on it's own, just as the piston would start falling back down in the cylinder, then if you gave the swing a push it would be as if the piston had proper timing set to ignite the flame somewhere after TDC to push the piston down just like you pushing the swing much easier.

Knock Retard is the PCMs way of protecting itself from literally blowing up the engine. So lets add the three Channels related to Knock:

• Knock Retard
• Burst Knock Retard
• Knock Learn Factor

[Gregski]

Timing - Knock Retard Histogram Properties

Now that we have our Channels we can build our graph to help us monitor Knock Retard. Same as before we can clone one of the existing sister timing graphs. Then we can tweak a few things:

Label: Knock Retard

Parameter: Knock Retard (which again the HP Tuner guys rename to Spark Retard)

Shading
High Value: 15 should get us started, we can adjust this later
Color: we want this to stand out so lets make it Red

[Gregski]

Timing - Knock Retard Histogram

And at this point we can go for a short 5 to 10 minute test drive around the block, these short test drives are essential to ensure our Channels work, our Graphs read data, etc. We don't want to set out to work on a Monday morning to log our first set of data only to find out some parameter did not come through because of a silly error.

Here is my sample data from my first test drive around the block. Nothing special, no knock, but we at least confirmed all the Channels and parameters are working.

[Custom 68]

Greg, I wanted to say thank you for this write up. I have been dabbling with HP tuners for several years but what you have here brings it all together. Very well written and helpful.
My recent jump is into the gen 5 stuff, that has proven to be tricky and haven't gotten too far along.
I am only tuning my own stuff and helped a couple friends get theirs going so it is just a hobby in my hobby so to say.
Again thanks
Dave

[Gregski]

Originally Posted by Custom 68

Greg, I wanted to say thank you for this write up. I have been dabbling with HP tuners for several years but what you have here brings it all together. Very well written and helpful.

You're very welcome I really appreciate you taking the time to provide this feedback, as I knew my mum isn't the only one reading this thread, ha ha. Funny thing is that after a while I start referring to my own thread for reference, ha ha.

Originally Posted by Custom 68

My recent jump is into the gen 5 stuff, that has proven to be tricky and haven't gotten too far along.
I am only tuning my own stuff and helped a couple friends get theirs going so it is just a hobby in my hobby so to say.
Again thanks
Dave

You are a brave man, I can't imagine the extra complexity in the Gen 5 stuff, I am quite happy beating the Gen 3s into submission still, great little engines.

[Custom 68]

Originally Posted by Gregski

You're very welcome I really appreciate you taking the time to provide this feedback, as I knew my mum isn't the only one reading this thread, ha ha. Funny thing is that after a while I start referring to my own thread for reference, ha ha.



You are a brave man, I can't imagine the extra complexity in the Gen 5 stuff, I am quite happy beating the Gen 3s into submission still, great little engines.

Yes after i have looked thru your post I am finding myself referring back to it as well.
I got a new daily driver a newer GMC Sierra that has the gen 5. Since I have HP tuners I decided I cant leave well enough alone so I am just sticking my toe into this. It is complex but something to look into and I am sure you understand that.
I do like the gen 3 motors they are great and have tons of potential. they will be around a long time and we will all continue to enjoy them.
Dave

[Gregski]

Timing - Knock Retard Histogram

and here is a sample of a log with some knock, truth be told this was supposed to be my longer drive, aka 20 or 30 minutes, but the log stopped recording, (hey just being honest with you all, it happens) let's just say that HP Mini netbook is no longer with us, ha ha!

anyway this is a good screen shot to share two observations regarding engine knock:

1. some engine knock is acceptable, after all if you log your factory tune for the first time you will see some knock, so the GM engineers are cool with that. I would think less than 1 degree retard is ok, that is for daily driving occuring here and there, if it's always in the same cell then by all means do something about it

2. False knock, without proper audio equipment to truly verify if our know is actual engine knock we really have no way of knowing. Again for stock engines and normal driving the stock knock sensors will do and we can rely on them, however if you were to heavily modify your engine or transmission you may experience false knock. This is yet another reason why minimal knock ie less than 1 degree can be tolerated.

[Gregski]

Timing - Retard / Knock Sensors

We will come back to the VCM Scanner and review more timing graphs in a bit, but at this time let's jump over to the VCM Editor and talk about the knock settings.

We find knock settings under two tabs:

Engine \ Spark \ Retard
Engine \ Spark \ Knock Sensors

Under the Ratard tab we find knock limits in the form of Knock Retard Amount and Maximum Knock Retard vs RPM (PE) or vs. MAP (Non-PE) It is important for us to acknowledge these but keep in mind just because the PCM can pull you in say 20 degrees to prevent engine knock that doesn't mean we can just set our Base timing willy-nilly and depend on the knock retard feature to make it right. Under this tab we also see Recovery Rate. When we get to performance tuning this may be a setting we revisit as it tells the PCM how long to hold the retard timing before returning it to normal, staying retarded for too long can rob you of some horse power.

Think of the Knock Sensors tab settings as the internals of the VCR (you 40 plus something year olds, lol) say you want to be an actor or a director, yes you need to know how to operate a VCR (pronounced YouTube of the 80s) but that doesn't mean you need to know how to build one, or know exactly how it works, other than we put the VHS tape in, and press Play, hewk on some machines it starts playing automatically. So for the time being just trust that the GM engineers knew what they were doing when they tuned our two knock sensors at the factory, remember this tutorial is for a stock(ish) LS engine swaps, not extreme builds. So for now we leave this tab alone, but this is where you would adjust knock sensor sensitivity.

[Gregski]

Timing - Knock Retard Amount

Here we take a look at the total Knock Retard Amount table found under:

Engine \ Spark \ Retard tab \ Knock Retard section \ Amount table

the PCM is willing to yank out up to 35 degrees of timing in my case, however this is as good of a time as any to mention the additional Multiplier tables, which take a complex system and make it even more complicated, ha ha

Engine \ Spark \ Retard tab \ Knock Retard section \ ECT Mult table

Directly to the right of this table is the ECT Mult table think of this table as that annoying friend that always chimes in when you try to tell a good story and corrects you all the time. So for example you say man I went to the Kings basketball game last night and they killed the Clippers, and your buddy goes, actually the final score was only 88-86. You get what I'm saying!?

So the ECT Mult table watches the engine coolant temp (there it is again the importance of keeping your engine properly cooled/heated) and for example when the temp is only 68 degrees and the PCM goes I'm gonna pull out 21 degrees of timing cause according to the Amount table that's what I gotta do at 800 RPM, the ECT Mult (your annoying buddy, goes) um not so fast the coolant temp is only 68 degrees at the moment so only pull out 75% of that 21 degrees.

Got it?

[Gregski]

Timing - Burst Knock Retard

Burst Knock Retard (pronounced: Predictive or Preventive Knock Retard) is a means of pulling timing out before a knock even happens based on an abrupt throttle change resulting in a sudden drop in cylinder airmass.

the Burst Knock settings are found under

Engine \ Spark \ Retard tab \ Burst Knock Retard section

How big of a cylinder airmass change needs to happen before the PCM can take preventive action is defined in the Enable Delta Cyl Air table (delta meaning change or difference) if you were to upgrade to a bigger cam, you most likely would increase the numbers in this table to make it more tolerant and less reactive ie less sensitive.

So for example once the PCM sees a 0.020 grams change at say 2,000 RPM it will consult the vs. RPM table to find out how much timing to pull out, and from what we can see at 2,000 RPM it will pull out 6 degrees of timing.

So that's how that works. For beginners and stock(ish) engines we leave these tables alone. If you pinky promise to only put high octane 91+ in your tank and want to add a bit of gitty up into your truck engine you can experiment with increasing the numbers in the first table Enable Delta Cyl Air in the lower RPM range say 1200 RPM and under.

[Gregski]

Timing - Knock Learn Factor

Think of the Knock Learn Factor like a fuel gauge that goes from 1.0 to 0 (yes I did say it goes from 1 to 0 which is backwards, but hey GM did not reverse\fix that until Gen IVs)

So when the Learn Factor is at 1.0 we are using the High Octane table values ie aggressive timing.

When the Learn Factor is low ie 0 we are using the Low Octane table, mild timing, that's one way to remember it.

Now the PCM will skew the timing by some factor when the Learn factor falls between 1 and 0 but that's for it to figure out.

[Gregski]

Timing

Here's a look at not a very happy Knock Retard graph.

Alright so armed with all this knowledge how do we actually get rid of the knock if we are experiencing some?