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.