HP Tuner Math Channel Help
 

So let me start by saying my first post here was a complete misunderstanding on my part with how I though things worked.

Now I'd like some help if possible from anyone willing with HP Tuners. I have created a math channel and histogram that shows "calculated AFR" and would like to know if anyone can compare it to an actual AFR sensor to see how accurate it is. I cannot install a wideband at the moment and was looking for another way to see the AFR at WOT and created it. It seems to be fairly accurate during acceleration, but i have nothing to compare it with. My local tuner shop only works on Mustangs, so until i can get a sensor and install it, I'm just looking for a way to see the AFR for now.
Any help would be greatly appreciated.
How do I share the information so it can be compared? Shows Invalid File when trying to upload

What are you using for calculated AFR? Narrow band readings?

Mass Airflow SAE divided by Instantaneous Fuel Flow Est. both in Grams per Second.

That can’t be used for tuning. At the very best it would be a rough estimate. If it was that simple, it would be used by everyone on the HPT forum You are using “models” for math.

So Im confused and that's why i asked if someone could test the math. If AFR is based on 14.7 parts of air to 1 part of fuel, then if you have the measured amount of each, would that not be the same? 14.7 pounds of air to 1 pound of fuel? Does it have to be burned in the combustion cycle to get AFR? If so why? I know this is not a perfect way, but I'm wanting to see how close it really is to being accurate. In my histogram it shows 15.1 to 14.7 at idle and low RPM speed, and drops under boost to 11 - 10.5.

As a further explanation, this may show as matching a command AFR but that is because it’s adjusting things using some of same parameters to make it match the models. You have to have an external measured point to adjust the models to “tune” or to know that it’s running like it should.

If the fuel pressure is off a little, your fuel flow estimates will be wrong for example. Variation in injectors will cause it to be off. MAF is its own model that has variations within it.

Ok i see and understand that.

Your measurements are not measurements, they are approximates from models, especially fuel flow. There is no fuel flow measurement. The whole secret to tuning is to get those models to match changes you introduced by changing things.

Even if your fuel flow was actually measured, it would be about impossible for it to be accurate enough to get you a number accurate enough to give you a useful calculation.

Ok so I have to ask, if there is no fuel measurement, why does the scanner show fuel pressure, commanded fuel pressure, injector flow, and how does the ECM in open loop know how much fuel to meter into the engine based on MAF to maintain an AFR from the factory without a wide band sensor?

No one willing to test this math channel to see if it’s close or not?

The computer is calculating things from the model using things it can measure and then adjusting things on the fly based upon what it sees. But if the model isn’t correct then it doesn’t know that there is a problem. And if you change parameters such as increasing boost, the models are no longer accurate. The models then have to be adjusted. What do you think is happening when things are “tuned”. If your math worked, why would it need narrow band o2’s?

I haven’t changed anything the car and tune are stock. So you’re telling me the ecu has no way to measure fuel and just goes off the tables programmed and guesses how much fuel to spray with “x” amount of airflow in open loop under WOT. That is ridiculous! Even a carburetor can meter the fuel without guessing and has no sensors at all.

It’s not just guessing, it’s constantly adjusting. And a lot of GM fuel injected vehicles don’t have a fuel pressure sensor at all. If the fuel pressure drops on those, it will see that it’s running lean when in closed loop, part throttle mode, and fuel trims will adjust. Long term trims will carry over and wot/enrichment will be guessed at, but the ECM has no way of knowing what the actual AFR is. You really need to read up on how GM oem systems work.

Your formula will be more accurate than one that doesn’t have a fuel pressure sensor measurement, but it still will be a guess. If it wasn’t just guessing, then there wouldn’t be any reason to tune a modified car.

But yes it really does this from pressure and airflow table look ups. There is a lot of math that also goes into it as it decides how much of each table to use.

Again, you think you have thought of something that no one else has, but none of this is new and if it was easy as you think, everyone would do if your way. I’m not getting a kickback from the wideband gauge people.

But if your car is stock, you can monitor your calculation and never know the difference. At that point it’s just a fun exercise. If you increase your boost level by more than a little bit, then it will matter.

And I understand what you are saying and I’ve been studying this ECM along with other tune files so I can get an understanding of it all. That’s why I asked if someone would be willing to test out this math channel and compare it with there wide band reading to see if it’s even accurate. But all I’ve gotten is lip service on how no one’s going to try it, how it’s a guess and the sensors aren’t accurate, and that the ECM just uses a set of variables in open loop WOT to basically guess at how much fuel to use. That ECM knows exactly how much fuel it uses with the airflow to maintain the correct AFR. Yes most cars don’t have a fuel pressure sensor, but I’m not work on one of those and don’t care about that as it’s not something I’m concerned with at this time. If I get a Pontiac 6000 SE, then maybe I’ll look at that configuration.

So, I agree with pretty much everything everyone said here. The calculated AFR is probably not going to match the actual AFR unless every variable is perfectly accounted for, and the engine perfectly consumes the delivered fuel under all conditions. In other words, it's not gonna happen.

I also feel you on wanting someone to actually test it, and prove it out to you. So, I did. Please see the screenshots below. This is a car I was doing some tuning on that has a good wideband in it. I created your Math channel with Mass Airflow divided by Instantaneous Fuel Flow Estimate, and because this car has ID1300x injectors, the entire tune is scaled in half, so I divided the result by 2 in order to make it come out right. The bottom-most row of graphing compares the the calculated AFR (white) against the wideband (red).

The results are about what I would expect. It trends the same as the actual AFR in most places, but they separate, sometimes significantly, in a few places. This is likely due to several of the factors mentioned in the posts above - the fuel flow is estimated, the airflow is a calibrated amount subject to inaccuracies, etc. I would not consider this approach a very useful tuning tool, narrow-band O2 sensors will give you a ballpark to shoot for in the absence of an actual wideband O2 sensor. If it's anything with boost on board, a wideband should be considered a requirement before any tuning occurs.

I like the idea though. And I love playing with Math channels - you can absolutely do some unique things there to get views into various pieces of engine/vehicle operation.

I’m not sure why you think you are smarter than everyone else, but I was trying to help. But after this second round of I’m smarter than everyone else, I don’t care if you try using the smell of the exhaust to figure out your AFR.

Doesn't the ECM get it's AFR info from the O2 Sensors and MAF sensor while in the close loop mode? Also on the Gen5 Zl's do they go into open loop mode at WOT? Thanks in advance for your answer.

Yes. Of course even closed loop on narrow band o2 sensors the ECM is still to some extent guessing. That is why it drives it from slightly rich to slightly lean when in closed loop. It only knows rich or lean, not an exact number or ratio.

Except it doesn’t use MAF for AFR. It uses a comparison of MAF to VE (actually on these I think VVE) to calculate how much fuel it thinks it needs, turns on the injectors for a length of time it thinks it needs, and then compares it to whether the narrowband say it was rich or lean. If it doesn’t get it correct, it adjusts things to “trim” it back to correct.

This is very much a simplified explanation. I could go somewhat deeper, but my knowledge doesn’t cover all of the details of all of the variables it uses in these calculations and table look ups.

Bro lol. You bought a $35-$40k car, $550 for HPT plus a laptop, but want to skimp on a $200 wideband? For real?

Also the LSA has been around for 15 years. There's nothing new to it. Playing with bypass springs pretending to increase boost and trying to trick the ECM into reading accurate AFRs may be fun and all, but the recipes for reliable power are out there...swap pullies, get bigger injectors/fuel pump and tune appropriately (with a wideband). It's very simple. No need to reinvent the wheel.

Thanks a million.

lol. Didn't you guys try to tell OP this last time?? In another thread?? It's so easy...Wow man.. :noidea:

Yes.

And in WOT and PE in open loop, it’s guessing at what to do for AFR as it doesn’t have a wide band to read, so how does it KNOW if it’s lean or not?

I'll try one more time even though I said I would pull out. It doesn't know in PE what the AFR is. It is just supplying the amount of fuel that was programmed in by the designers based upon what they expect it to need with a lot of table lookups, with an adjustment carried over by the LTFT from running in closed loop. This is why it has to have a wideband when running it outside of stock parameters. You have to adjust the model to now tell it how much fuel it needs at these new parameters.

I'm sure the original settings for WOT/PE where done with some combination of computer modeling and by using some version of an o2 analyzer, probably a lab grade 5 gas analyzer.

All of this is really the difference between it running in open loop vs closed. Closed loop means it has something to adjust by and tweaks things based upon AFR. Open loop is just following the programming. Reads pressure, rpm, temps etc, etc, etc and says it needs this much fuel.

So how much PSI are you at with all the mods you listed? I know there’s recipes out there and everyone is a cook, but nothing tastes the same when all the cooks follow the same recipe.
So as I stated before that you mentioned, I raised the boost with my first trick from stock to 9.25 psi and everyone is scolding my recipe, I did some research and math, and put a 10% lower pulley on two days ago, now I’m making 13.2 psi hitting the torque management boost disable, injectors are 112% and my cat temps are good. My MAF is just a few percent off at WOT, my calculated AFR for my stock ECM is within 1% of commanded lambda AND the PE table. I am getting a wide band soon, injectors, cam, springs, etc. So take your standard chicken soup recipe like the other 10 thousand have done, I personally don’t follow others with anything and revel with others telling me it can’t be done, you are wrong, or it’s impossible, then doing it. Can you personally design parts in AutoCad, have them made, cut weld and fabricate it all in stainless, build a rear differential, transmission, a twin turbo draw through carburetor system on a LS engine making 20 psi on stock pistons, get that ground up design and build to pass DOT regulations, get it titled, registered, and tagged without ANY help from others because there is no RECIPE for it and run it to 219 mph? Everyone said I couldn’t use hydraulic steering on a motorcycle, did it, everyone said I couldn’t use that transmission and differential setup, did it, everyone said the turbo system wouldn’t work, did it, everyone said you can use a single sided hub centric front wheel on swing arms for a motorcycle, did it. Do you know the exact PSI factory GM hypereutectic pistons will break ring lands no matter the AFR and .060” ring gaps? I do. Thanks for input.

Sure I can design my own parts and have them made by someone else. I could do that 30 years ago (when I was a Rocket Scientist, or at least an Engineering co-op with NASA). That has nothing to do with knowing how a GM ECM setup is done. You may know how you think it should be done, but that doesn't mean they did it that way.

Of course your commanded and calculated are following extremely close. It's calculating how long to turn on the injectors from cylinder volume and the commanded AFR. You are then calculating AFR from the same airflow and fuel flow parameters. The only reason it is different is a time lag.

And I understand this exactly, you stated what I’m looking at in this math channel I’m working on. It’s programmed with a known amount of air interring the engine, it injects a calculated amount of fuel to create a AFR without a wide band sensor. As I said in another forum, in the 1940’s they controlled AFR on 3000-4000 hp aircraft engines with both mechanical and exhaust superchargers on the same engine with pencils, paper, gauges and levers. The fastest aircraft engine ever in the SR-71 used gauges and levers so the pilot could adjust the AFR using airflow, fuel pressure, and EGT. I’m getting the wide band and some other things soon. I just for the life of me don’t understand why everyone knocks and beats on someone asking questions. I simply asked if anyone would compare the channel to a wide band reading. A few have and there cars are already modded showing the math reads lean in areas on there comparison. So I will do some tweaking on it. I know that it’s not going to ever be “perfect” as the math has no way to “see” the unburned fuel trapped between the piston and cylinder walls, but that can also be calculated to a degree. I mean really, drag cars in the 60’-80’s used EGT as a standard measure of AFR and so did every piston engine aircraft from the 40’s till the 90’s with carburetors. Some even had up to 30 psi boost and 20:1 AFRs. It’s not rocket science, it’s simple math. Thanks for the information.

See that’s a great response with useful information. I know it’s not perfect and was asking for the comparison so I can understand and tune the math. It was my first attempt and math channel and I know it needs some work. As far as understanding the ECM, I’m studying every aspect of it and how every table cell by cell is related and calculated for AFR, MAF, injector timing, spark, knock, torque management, TCM commands, everything. But I still believe that the AFR can be accurately measured with the math to a very close percentage if I continue to work on it.

You do realize that HPT only shows you a portion of the tables actually used in the ECM. Probably more than most of the vehicles, but still a lot of tables they never touch.

It's not my car so tweak away at your formula and try and tune it to some high boost level using it. It should be very close in closed loop mode, where the wideband isn't needed. I will weigh in on any post that portends to say how great it works as a warning to those who don't know better.

Don't just pop in at random on some thread for something like this. Either classifieds or at least start your own thread.

You saw that I did your test above, right? It works, kinda, but isn't reliable. At the end of the day, calculating AFR is a calculation on what you're delivering to the engine. You can get it more or less accurate depending on how much you measure, and how many variables you account for, but ultimately, it's what you gave it. Just because you gave measured the air and fuel going in at a 12:1 ratio doesn't mean that's how it actually worked out - there are a lot more variables going on in the fuel, the air, and inside the combustion process that can alter that further. What it actually burned, and the resulting AFR, are always going to be a bit different, and that's why tuning with the wideband makes so much more sense - you need to check your result, and adjust to it.

This is what the OEMs do - they calculate what they need for fuel based on a given amount of air, and then they provide that to the engine. But they know it won't always be spot on for all sorts of reasons, and so there is a constant feedback loop of monitoring the result, and continuing to adjust the fueling accordingly. Tuning on a calculated AFR alone is never going to be a good idea.

Isn't that what it basically is doing in OL? With the adjustment in LTFT from closed loop?

That's exactly what it does in open loop - it fires in a given amount of fuel based on a calibration against airflow, with no feedback loop. It does consider the LTFT, and adds fuel if the LTFTs were also doing so. Its not, however, how the initial calibration would be setup, and it's not how it would be modified after the fact.

Tuning for WOT is critically dependent on using an external sensor to properly calibrate the air-fuel ratio. It's also why when I tune I will tend to defer slightly towards the safe side of the AFR, in order to allow for some unforeseen variables coming into play that would alter the AFR in a negative way. The power to be gained or lost in a half a point of AFR is fairly minimal. For a race application, sure, you get all you can. Those cars also typically have the best fuels and maintenance routines, and are kept under high levels of oversight. For a street driven car, I will absolutely roll 2-3% of WOT fueling back in the calibration once it's finished as a buffer, it might cost a couple horsepower, but it also gives the engine a better shot at a long happy life with a less involved operator that might neglect a fuel filter, run some less than top tier fuel, etc. I'll do the same with the spark - we'll get that maximized, and then take just a small step back for a bit of a safety margin.

It's also worth noting that we're talking about 5th gen Camaro's here. There are plenty of other vehicles on the road that utilize closed loop fueling in all modes of engine operation, including WOT/power enrichment. It's a better strategy - you'd have to ask GM why they went with their scheme. It's usually related to money...

Somehow I interrupted "Tuning on a calculated AFR alone is never going to be a good idea" to mean "fueling based upon desired AFR". Not sure how I did that, but that is really what you answered to anyway.

Seems I hit a nerve here. Relax, boomer lol.

Yes I have access and the knowledge to do all those things. It's not overly difficult. I'm not here for a dick measuring contest. If you have relevant questions I'm happy to help.

To answer your question my car makes 15 psi. I hope that helps with your wild endeavors :)