Power Enrichment Question

[sgod1100]

Can you give me a layman version of what hysteresis does? What a higher value does and what a lower value does. MAP, RPM, and TPS are easy to see.

its the amount of kpa (map) drop required from your set point to get out of PE. So the larger hysteresis the longer it will stay in PE once your kpa reading goes below your set map value. At least that's the way I understand it

[blindsquirrel]

Hysteresis is how far it has to drop before it disables, so that it isn't in a situation where it turns on-off-on-off-on-off without any real (meaningful) change in the load/throttle angle.

[TheMechanic]

So typically are you changing these "Hyst" by a lot?
I have my typical settings I use for PE that work well but never changed Hysteresis.
What about the "Enrichment Throttle". I've never changed that.
This is just a random stock file for explanation only
PE.JPG

[07GTS]

the throttle is from enabling PE u have to drop 0.5% throttle for it to disable from the enable point, i think the throttle % will be area also so dosnt need to be big to make a decent affect, i dont notice it much with PD blower but with the turbos if ur in PE and TPS is steady it can vary in the MAP and sometimes cause engine to jerk going in/out of PE so a wider map hyst can help that

[blindsquirrel]

None of those settings will make it do anything magic, they will only stop it from doing things it shouldn't. If it's not doing things it shouldn't, and it's pretty hard to imagine a situation where it would be able to, then they don't need to be touched.

[hjtrbo]

Pretty sure your axis might be wrong in this one Nathan. It should be represented as an S shape, so area going vertical and tps horizontal. Unless they just did it this way in the gen 4's? At least this is how they define it in the newer ones...

Attachment 142885

The table I'm displaying is the tps calibration against the effective area. Hence why tps is on the y axis. I'm sure there was furious debate as to which way to do it. This screenshot shows the s shape if I flip the axis over. Same data set as my earlier screenshot.


And finally the tables in my tune. Also included the trans mapping as that always had me buggered when working out shift points to tps back in the day.

[GHuggins]

It's right. The table I'm displaying is the tps axis calibration against the effective area. Hence why tps is on the y axis. This screenshot shows the s shape if I flip the axis over. Same data set as my earlier screenshot.

I know it can be shown either way. It's just usually described or shown as the S-shape even though GM plots it vertically in the ones I've been shown. Of course either is politically correct Just easier to make changes for the TB changes to the S one

[hjtrbo]

Made a edit to my reply to you.

[GHuggins]

Yeppers, that's how I've always seen them. What's nice about tables like that in hpt if you change one it automatically updates the inverse for the other...

Hmmm. That transmission one does look appealing........

[hjtrbo]

Hmmm. That transmission one does look appealing........

It sure does, I'm going to shift it around and see if it affects rev match.

[GHuggins]

It sure does, I'm going to shift it around and see if it affects rev match.

You've got, well part of the tool, fix the models Who knows, I'm not sure how that one's defined. You're the only person I know getting in on the transmission side of things. It may affect it???

[hjtrbo]

You've got, well part of the tool, fix the models

Pestering is like frontal surface area. The more you add the slower things get.

[GHuggins]

Pestering is like frontal surface area. The more you add the slower things get.

LOL... Yes, but the better the end result

[edcmat-l1]

None of those settings will make it do anything magic, they will only stop it from doing things it shouldn't. If it's not doing things it shouldn't, and it's pretty hard to imagine a situation where it would be able to, then they don't need to be touched.

The OP seems very interested in lots of tables that don't need to be touched.

[blindsquirrel]

But if you just make everything more, won't that be better?

As to general theory about Power Enrichment, I used to live in the world of carburetors (I am old. I'm sorry.). In a typical Holley carb there is a power valve (PV). When vacuum decays as the throttle and load increases, the PV opens and uncovers a second set of jets. At least, that's how it's commonly understood. But that is actually backwards from what it really does. No, main jets plus PV jets is the carb's natural state; what the PV allows for is leaning out during light throttle/low load cruise. High vacuum closes it, instead of low of vacuum opening it.

Carbs are different from EFI in that opening the PV on a carbureted engine at idle, when the main circuit is not flowing, will do nothing at all to the mixture. It can only add fuel when the mains are flowing, which only happens according to airflow (actually airspeed). Not so with EFI - that fuel gets squirted in whether the engine can take it or not. So, we need more controls to disable PE when it's not needed or wanted. Like not having the RPM Enable so low that it's active while cranking, Throttle settings high enough that it's not constantly on and off and on again in normal in-town driving. Just let it work when engine load is high enough that the engine truly needs it's normal full power mixture.

It would probably work better, or be more intuitive, if PE used Cylinder Airmass instead of MAP. Airmass is a better indicator of how much load there is and is largely independent from RPM or throttle opening. MAP is pretty close except when it's not, which is why there are so many overrides and delays and conditions and whatnot.

[Allen Vos]

The OP seems very interested in lots of tables that don't need to be touched.

Allow me to correct you kind sir.....

I am interested in lots of tables in the interest of learning what they do.

How do you think people learn? Is there a problem with wanting to know how things work and why they do the things they do?

I'm sure you didn't know everything when you first started out at this.


Sometimes we need to try things out and make mistakes along the way to learn.

These posts will be valuable information to people like myself that are learning.

Seems kind of dumb to me to only understand 1 or 2 things that are important in the PE area and not put an effort in to understand everything else around it.

I'm pretty sure by what I have read PE denfinletly needs some changes after a cam swap, so why not try to understand everything?

It funny when I went to trade school to be come a mechanic some 20 plus years ago they taught us every little piddly little detail of how things work which is invaluable to being able to diagnose and figure things out.


That is how I learned and how I will continue to learn things.

[Allen Vos]

Look under [Engine > Fuel > Power Enrich > Throttle > Hot] to see your TPS report for mapping PE to throttle opening.

That table that hjtrbo posted represents the geometric relationship between throttle percentage with how much the throat of the throttle is exposed to allow air to pass. This is the difference between the throttle body area and the throttle blade area. As the blade rotates the "shape" (from the airflow perspective) changes from a circle to an ellipse. So a 10% change in throttle does not equate to a 10% change in area for air to flow since we are dealing with a concentric ellipse inside a circle). Note the TPS % is linear on the Y axis while the Effective Area % on the X-axis is not linear (perhaps it is logarithmic). Anyway this is not something you should edit by direct means.

But either way, you can see that when table [ECM] 12420 says ~13% for effective area...it is really mapping to about ~43% on the TPS side.

I was aware of the ECM 12420 table for PE TPS values as it seems thats all my car uses to control PE from stock.

What I was referring to was the table that HJTRBO posted, and was wondering if that table is available in VCM editor?

I would not have know the value of PE TPS to regular TPS if he hadn't posted that table.

Its great to have this table though.

Does that table apply to all gen 4 LS motors?

[GHuggins]

I was aware of the ECM 12420 table for PE TPS values as it seems thats all my car uses to control PE from stock.

What I was referring to was the table that HJTRBO posted, and was wondering if that table is available in VCM editor?

I would not have know the value of PE TPS to regular TPS if he hadn't posted that table.

Its great to have this table though.

Does that table apply to all gen 4 LS motors?

The tables that Hjtrbo posted are not available in the editor and respectfully, probably shouldn't be as bad shit can happen when they're wrong. They define "effective" throttle area vs tps for the throttle body or in other words part of the throttle model used to define the throttle profile. The baro tables, which are available, fine tunes that... To access tables like that you need to have User Defined Access and know someone who can find them or find them yourself. Trust me, that part isn't easy... That particular table only needs to be changed for different throttle bodies and even then you can manipulate other things to work around it. ETC scaler alone should get it close enough and then you can use the baro tables to work out any kinks.

I'm told throttle area is incorporating sonic airflow into it to "some extent". Don't know if that's true or not. Seems to be from the tables I've seen using the same throttle bodies with different intake manifolds. Trucks to cars are a prime example in that regard. All of this is used to define throttle position. Sonic airflow is pretty much the same thing as "port air flow" from everything I've found, which is looking at air pressure in front of and behind, temperature in front of and behind, MAF, manifold volume and I think a couple of others to determine the speed of air going into the motor. All of this plays into throttle operation.....

[Allen Vos]

The tables that Hjtrbo posted are not available in the editor. They define throttle area vs tps for the throttle body or in other words part of the throttle model used to define the throttle profile. The baro tables, which are available, fine tunes that... To access tables like that you need to have User Defined Access and know someone who can find them or find them yourself. Trust me, that part isn't easy... That particular table only needs to be changed for different throttle bodies and even then you can manipulate other things to work around it.

I'm told throttle area is incorporating sonic airflow to "some extent". Don't know if that's true or not. Seems to be from the tables I've seen using the same throttle bodies with different intake manifolds. Sonic airflow is the calc, combined with area and everything else, to define throttle position. It's pretty much the same thing as "port air flow" from everything I've found, which is looking at air pressure in front of and behind, temperature in front of and behind, MAF, manifold volume and I think a couple of others to determine the speed of air going into the motor. All of this plays into throttle operation.....

Oh I'm not interested in changing it, I was only curious where it was in VCM editor , if it was.

The only thing I feel needs to be changed is the Min map value to activate PE

and potentially the ECM 12420 PE TPS vs RPM table.

Just wanted to understand this whole thing inside and out is all.

[Cringer]

Oh I'm not interested in changing it, I was only curious where it was in VCM editor , if it was.

The only thing I feel needs to be changed is the Min map value to activate PE

and potentially the ECM 12420 PE TPS vs RPM table.

Just wanted to understand this whole thing inside and out is all.

I will always err on the side of engaging PE earlier than needed rather than later. As engine load (cylinder airmass) increases, so does cylinder temperatures during the compression stroke. The increased heat increases the chance of detonation.

So in my opinion, engaging PE early keeps the temps at bay from the get go. Which is better than delaying PE, which allows temps to increase only trying to cool them down after it is already hot. So if you want to delay PE, then perhaps you should do as GM does and think about keeping Burst Knock on.

I don't think anyone is here is overly concerned with MPG or emissions (at least to the extent that the OEMs are forced to)...so what is the advantage of staving off PE?

--

The table is not available since it is a physical characterization of the geometry of the throttle body. If you were to mess with that, it would throw off the ECM's entire understanding of torque management and idle control. The way you influence these factors are primarily through these scalar values:

• [ECM] 2154 - Idle ETC Area Scalar
• [ECM] 2173 - Idle Effective Area Max

If you ever do decide to upgrade to a larger throttle body, the new Nick Williams 103mm (and also the Katech 103mm which is made by Nick Williams) has been designed to work with the OEM values here (at least if your Gen4 originally came with a gold blade TB). This cuts down on the tuning and quirkiness of a large TB. You will find many posts in here with people struggling to get their NW 102 TB to act right...and lots of good insight from GHuggins on how to tune it.