yeah i got ya, i might have said something wrong. but is pe just for WOT i think thats the only area that has yet to be covered in here

 

PE has TPS and other thresholds. It is not strictly WOT. It could throw your trims off then tuning VE. I don't feel that it is a necessary step for my tuning purposes. I can't really say which way is better.

 

anyone know any more details on PE or where i can find it?

 

what all do you need to know about PE? It basically throws the car back into open loop operation (with the exception that it will trim upward if it needs to) You use it when you want to command richer AFR for power production. Stoich operation is for emissions but our cars make the power in the 12.0-13.0 AFR range.

 

WS6FirebirdTA00 - In regards to tuning the MAF, one thing comes to mind that I haven't seen mentioned in this thread - How the MAF itself works.

If my understanding is correct, the MAF heats the resistors (in the air flow path) to a givin temperature. The MAF circuitry will keep these resistors at the same temperature at all times. The circuitry then monitors how much voltage it takes to keep the resistors at the fixed temperature and then translates that voltage to frequency. The PCM reads the frequency supplied by the MAF and pulls the mass air flow rate from the MAF table.

All that being said, since the MAF is actually measuring the voltage to maintain a given resistor temp., wouldn't that count for all the variables in air density you've mentioned? Air density and humidity will alter the airs ability to absorb heat, right?

 

This is what I'm saying: the MAF measures mass. It doesn't matter if this mass ir cold or warm, dense or not. Mass is mass. The MAF also has a thermoelement that compensates for themperature changes.
With an higher pressure there will be more mass cooling the wires, so it's automatically compensated.
If it was a propeller of course it would be necessary to consider other things. But not the MAF.

 

I almost posted that myself, but I wasn't sure how everyone would react. That is my take on it as well. And yeah...that does make sense about the humidity too.

 

this is true, that was one of the things i was trying to figure out, if the computer had a way to compensate, if it didnt then there would really be no point for the maf you know? thats a great point though thanks

 

can you explain your theory more? im not saying you are wrong but from what i have learned in the equations it is dependent on many factors. the mass is vairable with different things. i just may be mistaken and if i am please correct me, but i thought the density played a very large role in the MAF rate and if it does my book says right here that the given numbers are for 25* C and 1 atm. so those would have to be factored in. im not saying i am right or you are wrong, but just trying to figure this out, not only for my car but it is what i wanna do later on in life so i would really like to understand. the mass of air is determined from the density for a given volume. and the density equation has temp, press and vapor pressure as variables. get why im confused?

 

What he is saying is that as the air pressure goes up, the air is more dense, thereby cooling the wire more and requiring more voltage to maintain the temperature. Same thing happens if the temp goes down or the humidity goes up.

The MAF does not know which of the three happened, all it knows is the mass of the air went up. The wire is cooled by the mass of the air moving past it. More mass (for whatever reason, pressure, temperature, or humidity) means more cooling. PCM compensates.

 

found this right up right here, figured i would post for all, makes sense now. our tables come out in a measure of frequency right?


The Mass Air Flow Sensor is probably the best way to measure the amount of air an engine takes in (engine load). This sensor not only measures the volume of air but also the density as well. Ford & GM are using engine management systems based on this sensor.

There are two common MAF sensors used today. One produces a variable voltage (analogue) and the other produces a frequency (digital). In either case their operation is similar. Both systems work on the "hot wire" principle. A constant voltage is applied to the heated wire. This wire is positioned in the air stream or in an air flow sampling channel and is heated by the electrical current that the voltage produces. As air flows past it, it cools down. This causes its resistance to drop. The drop in resistance allows more current to flow through it in order to maintain the programmed temperature. This current flow is changed to a frequency or a voltage which is sent to the ECU and interpreted as air flow. Adjustments for air temperature and humidity are taken into consideration since they also affect the temperature of the heated wire or film.
Humidity affects the density of air, humid air is denser than dry air. Air temperature affects density since colder air is more dense than warmer air. Many systems use an air temperature sensor to compensate for this. Some MAF sensors use an internal "cold" wire to send ambient temperature information to the computer. Some use an intake air temperature sensor in the manifold or the intake piping. This sensor is almost always NTC (negative temperature coefficient). That is, it's resistance goes up as air temperature goes down. This "thermistor" works just like a coolant temperature sensor



now just to use some of my electrical crap i learned to figure out how many Hz is equal to 1 lb/min. i have a feeling this could be done from the stock settings though, stock meter and all, right?

 

YESS!!

NO
The density of air only depends on the pressure (and on it's composition too, but as long we stay on the Earth it will be the same )
The humidity increases the thermal coefficient of air and this will trick the meter. That's why you have an accurate reading only if you dry the air prior such a meter. The error will be just a few % and the O2 will correct it.

THEORETICALLY YES...
But also new cars don't have all LTFT at 0%, this means that it's not exactly right. Every flow meter needs a piece of straight pipe in front of it. Much longer than what we have. We have a screen to calm down turbulences but it's only a compromise between accuracy and place.
Usually you need 5 times the diameter, it means a round a straight pipe of about 16 inches...
I think the most precise meter we have are the O2 sensors: look, in the PCM strategy they always have the last word. No matter what the MAF does, no matter how the VE is set.

In my opinion the PCM uses every sensor at the same time and try to get the best out of it. Using more sensors will also tell you if something goes wrong, you can check a single sensor looking at the others.
That's why it's important to tune every tabe (VE, MAF, IFR and so on) or the PCM will think something is wrong.
The result? Bad response, tip in KR, bad mileage...

 

Ive read this thread and understand the issues and mathematical principles you are talking about. But I will offer a pragmatic view and suggest you are all overlooking an important factor when fuel trimming.

Firstly, GM would have already gone through this mathematical mumbo jumbo to accurately flow rate these MAF meters. The important thing is you get a MAF with a known calibration. You can bet that whever you think it needs to be it will only be out by a few %. So leave it stock until you have determined by how much it is out.

Understand how closed loop fuelling works before thinking that the VE or MAF table is out.

Before anything you need to ensure your O2 sensors are swinging nicely at idle and in motion. If not, alter their gain by modifying the Base O2 Sensor Airflow Mode until it does.

The move into the Base Airflow Mode. The VCM only has a resolution of to 9 cells for O2 switching. You can this by opening the O2 Closed Loop Proportional base vs Airflow Mode table. The Airflow Mode maps to a g/sec Mass Ariflow via the Base Airlfow Mode table. What you want is even and highest resolution for closed loop fuelling up to Airflow Mode 16 spread over each of the 9 cells.

You need to alter your Base Ariflow Mode to suit your CAI plumbing to achieve this. I have 3 Airflow Modes fuelling LTFT cells just off idle and to 12 g/sec. The I spread the remainder Airflow Mode Cells so that there is resolution of 2 cells per Fuel Cell. This will result in rock steady fuelling in closed loop.

My LTFTs are within +/-1 at all times. My STFT cells are mostly 0 and are rock steady under ALL driving conditions.

Having nailed your fuelling cells and calibrated the closed loop switching Airflow Modes for max. resolution for each Fuel Cell you can modify your MAF table by the total average % of LTFT as shown in the LTFT histogram in HPTuners. Mine was showing up to 2% so I scaled it up by 2% to result in consistent 0 and +/-1 LTFTs across the board.

If I was performing a SD tune I would then calibrate my VE table so that it is inline with my derived Dynamic Air calcs. I am taking the approach here that the MAF is the correct and the VE table is out - not the other way around. Since my logged Dynamic Air calculated off the VE table was already inline with my MAF g/sec I didnt need to and just smoothed it out a bit.

I now have excellent throttle response and fantastic fuel economy. Closed Loop fuelling is rock sold steady and won't change cell by cell - a common frustration when fuel trimming. It will change as the ambient temps. vary but by no more 1% per 10*C. So if you get it set at LTFT 0 for 15*C you can be sure you have good fuelling from -5*C to 35*C - pretty much all driving conditions.

This is the approach I took and it has worked tremendously well. It is a new approach to fuel trimming and so would appreciate your feedback on your successes/failures.

I am inclined at this point to believe the Base Airflow Mode table is the key to closed loop fuelling rather than the MAF. Base Airlfow executes closed loop fuelling - not the MAF. The MAF merely provides g/sec measures to tell it what to do. Kind of like a car needs a driver.

 

fwiw, I've chosen the following route to dial in my new motor

Set the IFR table: Started with the stock injector flow table, then scaled to compensate for the larger injectors

Set the VE Table: Used the SD tuning (based on LTFT'S) procedure to rescale the VE table

Set the MAF TABLE: Log dynamic air flow g/s (This is the g/s value of the VE table) and MAF Frequency to scale the MAF table.

Tune the Idle tables: By means of the idle transition tuning procedure

So far I have been able to complete the IFR, and am very close to completing the SD Tune (this has been rather time consuming for me )

Back to the topic at hand, It seems the only way for us low budget (as compared to GM's budget) engineering types to rescale our MAF tables is to get the IFR and VE tables in line first. If these two tables are in line, then the task of back calculating the MAF tables should be cake.

I would like to know how GM goes about doing this though.

 

MNR-O - You bring a good perspective to this thread. Based on this information, I would have to say the correct tuning approach will depend what you are starting with.

In my case, I unknowingly bought a severly bastardized '00 WS6 M6. At 53k miles, the motor was consuming oil at a rate of 1qt / 100 miles . I also discovered the MAF had been descreened, gutted of most thermistor bracing, and has ported MAF ends (this has been replaced with a GM 85mm unit). Upon initial inspection of the tune, the MAF tables have been rescaled by ~ 101%. All this adds up to a full bolt-on 383 with low numbers.

So given my scenario, I know my VE table, MAF table, and MAF are no where near close. The only logical starting point I could find was with the IFR tables - and this takes me to my previous post.

My question is, knowing the MAF, MAF tables, and VE tables are wrong, at what point would you tune for CL fueling?

 

see, i plan on going bcak to stock maf ends to get all the other numbers correct, like you said, gm did this from the factory so its right when in stock trim, but i wanna put ported ends on there so i need a way to accurately account for those. and with everythign else just right and the only change being the MAF ends, this should be accounted for correctly. i will do a SD tuen with the stock maf ends to get number right and find out the ve for those maf settings, then i will do an sd tune iwth the new maf ends on and then correct the maf table accordingly.


....calibrated the closed loop switching Airflow Modes ....im still a little unclear on what this is.

....Closed Loop fuelling is rock sold steady and won't change cell by cell....

MNR-0 could you explain some more about this? it sounds very interesting. im just not quite sure i follow.

 

MNR-0,
"alter their gain by modifying the Base O2 Sensor Airflow Mode until it does"

"The move into the Base Airflow Mode."

"You need to alter your Base Ariflow Mode"

Are those functions of HPTuners? I don't see this in Edit At least not in my 98 edition.
My approach is same as TAQuickness: IFR, then VE then MAF. Once it's done I check all the stuff again then I stop it becose this thing is addicting and you never stop if you look at every little thing.

This of 1% every 10*C I don't know... I'm checking the VE table those days and the low load cells (I mean the MAP vs RPM cells) are different everyday. +/- 0.7% or so. The temperature changed between -1 and +3 *C.
So after a couple of days of logging and changing the VE table I made an average, smooth it a little and leave it like that.
I'll do the same in summer (30*C) and average it to the winter settings and then I'll definetly stop it. As said it's addicting...

 

Nicely put. My wife has been looking for rehab groups for me

 

before doing all this tuning stuff woudl you guys recommend taking some electrical contact cleaner to the MAF? i would think there could be some **** on there that could cause misreads.

MNR when you get back on here i would like it if you can explain your process a little more to me. i like the way it sounds

 

Definately clean the MAF. This is a pic of what my "stock" MAF looked like when I replaced it with a GM 85mm MAF. Notice all the **** caked up on it.