Is Your Car Tuned Correctly?

[Shaun@AED]

For those that never adjust the MAF transfer function, please explain how you address the following situation...

Pressure @ injectors = 40psi

AFR (Commanded)
3000 RPM = .78
4000 RPM = .78
5000 RPM = .78
6000 RPM = .78
7000 RPM = .78


AFR (Actual)
3000 RPM = .75
4000 RPM = .79
5000 RPM = .83
6000 RPM = .80
7000 RPM = .77


The error is non-linear. It is both below and above the target lambda for each cell. You wouldn't adjust a linear injector slope in this situation, would you? Do you adjust the open loop fuel table proportionally at each load/rpm cell? That would make your commanded lambda fluctuate, in an effort to create a stable AFR. That doesn't seem right.

I am curious to see how those who NEVER touch a MAF transfer function account for non-linear errors in fueling.

I do agree it is nice to have a known, accurate MAF transfer function. I like the current Pro-M stuff for cars that I work with. I run one on my personal car. They come with a data sheet with an air model built with respect to the meter and air filter that is to be used on the vehicle.

When it comes to multiple vehicles and/or multiple MAFs, should you always assume that repeatability between two MAF transfer functions is always 100%? How about when it comes to blow through?

Sure...there's the HPX Tool and there's other utilities out there based upon tube diameter. There are also each of our own previous air models that we have used in prior combinations. Each of these are starting points.

To say that every PCM will read airflow the same is dismissing several different tolerance factors and assuming 100% repeatability among every meter. That is not a comprehensive method. It is poor practice, in my opinion.

Fun topic. Not sure if my car is tuned correctly. Depends who you ask, according to this thread.

Slopes, Intercepts, mass of air charge
(VE data)

 

[racerbox77]

Subing in so I can read this novel later and learn some things.

 

[MichaelFreedman]

For those that never adjust the MAF transfer function, please explain how you address the following situation...

Pressure @ injectors = 40psi

AFR (Commanded)
3000 RPM = .78
4000 RPM = .78
5000 RPM = .78
6000 RPM = .78
7000 RPM = .78


AFR (Actual)
3000 RPM = .75
4000 RPM = .79
5000 RPM = .83
6000 RPM = .80
7000 RPM = .77


The error is non-linear. It is both below and above the target lambda for each cell. You wouldn't adjust a linear injector slope in this situation, would you? Do you adjust the open loop fuel table proportionally at each load/rpm cell? That would make your commanded lambda fluctuate, in an effort to create a stable AFR. That doesn't seem right.

I am curious to see how those who NEVER touch a MAF transfer function account for non-linear errors in fueling.

I do agree it is nice to have a known, accurate MAF transfer function. I like the current Pro-M stuff for cars that I work with. I run one on my personal car. They come with a data sheet with an air model built with respect to the meter and air filter that is to be used on the vehicle.

When it comes to multiple vehicles and/or multiple MAFs, should you always assume that repeatability between two MAF transfer functions is always 100%? How about when it comes to blow through?

Sure...there's the HPX Tool and there's other utilities out there based upon tube diameter. There are also each of our own previous air models that we have used in prior combinations. Each of these are starting points.

To say that every PCM will read airflow the same is dismissing several different tolerance factors and assuming 100% repeatability among every meter. That is not a comprehensive method. It is poor practice, in my opinion.

Fun topic. Not sure if my car is tuned correctly. Depends who you ask, according to this thread.

If """"ALL""" fuel adders are disabled, then the MAF curve needs adjusted. In that case, the airflow that the motor is seeing is different than what the meter is commanding. If a flow bench was available, I would flow the meter with the intake piping and most likely you will see the difference between what is in the PCM and actual values.

Mike

 

[04sleeper]

I don't know about anyone else, but I tune all my cars just like this. :bored:

 

[68fastback]

...5.0 development torture testing!

...note the entire to-be-production factory airbox on there too.

Well, allrighty then!! ;-)

 

[truckguy]

For those that never adjust the MAF transfer function, please explain how you address the following situation...

Pressure @ injectors = 40psi

AFR (Commanded)
3000 RPM = .78
4000 RPM = .78
5000 RPM = .78
6000 RPM = .78
7000 RPM = .78


AFR (Actual)
3000 RPM = .75
4000 RPM = .79
5000 RPM = .83
6000 RPM = .80
7000 RPM = .77


The error is non-linear. It is both below and above the target lambda for each cell. You wouldn't adjust a linear injector slope in this situation, would you? Do you adjust the open loop fuel table proportionally at each load/rpm cell? That would make your commanded lambda fluctuate, in an effort to create a stable AFR. That doesn't seem right.

I am curious to see how those who NEVER touch a MAF transfer function account for non-linear errors in fueling.

I do agree it is nice to have a known, accurate MAF transfer function. I like the current Pro-M stuff for cars that I work with. I run one on my personal car. They come with a data sheet with an air model built with respect to the meter and air filter that is to be used on the vehicle.

When it comes to multiple vehicles and/or multiple MAFs, should you always assume that repeatability between two MAF transfer functions is always 100%? How about when it comes to blow through?

Sure...there's the HPX Tool and there's other utilities out there based upon tube diameter. There are also each of our own previous air models that we have used in prior combinations. Each of these are starting points.

To say that every PCM will read airflow the same is dismissing several different tolerance factors and assuming 100% repeatability among every meter. That is not a comprehensive method. It is poor practice, in my opinion.

Fun topic. Not sure if my car is tuned correctly. Depends who you ask, according to this thread.

Personally I would adjust the maf as long as it doesnt create a step or hump in the maf curve. The other way to do it would be to command an artificially rich lambda in the base fuel table. Which way is more correct? I dont know that there is a correct answer to that question. Think about it yourself and figure out what makes more sense to you.

Look at it a different way. In your scenario, the largest correction is a 6% correction in airflow which is at 5k rpm. Probably well within the margin of error of things. So what happens if you put the correction into the maf curve? 1. You richen fueling up (.83 is too lean for a supercharged car imo...) 2. Load goes up and as long as you arent on the top row of the timing table, timing should go down. Neither is going to hurt the motor. As a matter of fact, both would actually protect the motor....I would prefer that scenario if it were my car than commanding a .75 in the base fuel table to get a .78 actual but that is me. The point of the conversation is to get people to think about what makes sense them....

Now at 3k and 7k where it is slightly rich, I probalby wouldnt worry about it too much especially if 3k is the tip in point but again that is just me....Really what is a few percent rich going to hurt? Absolutely nothing....Worst case you leave a few hp on the table.

...yep .78 lambda = about 11.4 A/F ...but are those 'actual' numbers hypothetical? I'm wondering if the 'actual' could truly be actual with it was a fully flowed intake.

You would be correct if it the fuel contained zero ethanol. On todays 10% ethanol blends it would be closer to 11.0. This is really why it is important to look at things in terms of lambda rather than afr. 11.0 on 10% ethanol fuel is pretty much the equivalent of 11.4 on pure gasoline. Looking at lambda puts everything on the same scale so you dont have to worry about the correction factors. Also, widebands are actually lamda sensors and they get hit with a multiplier to display afr. In order for the afr display to be correct, the multiplier used needs to be the same as the stoich point of the fuel being used.

 

[po-po 5.0]

Most of this knowledge is spot on, other is dated. One example of the dated:



Correction: You can run any MAF with any injector.

Let's say you are running a stock car with 15psi of boost. You decide you want to use E98 fuel. In part you may need bigger injectors, correct? This doesn't mean the MAF has to change to match the injectors. The MAF does not need to match the injectors. The MAF does need to have enough range to measure the airflow present.

I think you're missing the point. Back in the Foxbody days, certain MAF manufacturers would sell you a MAF housing "calibrated" for a certain injector size that you'd drop your stock MAF electronics into. This "calibrated" housing allowed you to run larger injectors without making any changes to the ECU. It did this by having, say, a 19/39ths as large sampling tube (for 39# injectors in place of 19#ers) vs stock.

This is back when MAF housings were metal, and the sampling tube was integral to the housing instead of the sensor.



The OP is saying that this is a bad way to do things on modern cars...and actually it was a bad (but accepted...and people still talk about "calibrated" MAFs today) way of doing things back then.



So yes...you're right, you CAN use any MAF with any size injector so long as you tell the ECU what MAF and what injector you're using. The old concept of "calibrated" MAF housings was a way to avoid having to actually make any changes to the ECU.

 

[04sleeper]

And here's why that didn't work correctly back in the Fox days.

www.oldfuelinjection.com/files/How_MAF_works.doc


:read:

 

[Eric@HPTuners]

And here's why that didn't work correctly back in the Fox days.

www.oldfuelinjection.com/files/How_MAF_works.doc


:read:

Calibrated MAF's weren't perfect on an old EEC-IV, but it did serve it's purpose, when there was no real solution to properly recalibrate the PCM. WOT spark on the Fox body was a function of RPM, so calculated load was not nearly as important as it is today.

 

[04sleeper]

Calibrated MAF's weren't perfect on an old EEC-IV, but it did serve it's purpose, when there was no real solution to properly recalibrate the PCM. WOT spark on the Fox body was a function of RPM, so calculated load was not nearly as important as it is today.

I understand that but driveability suffered.

 

[Eric@HPTuners]

I understand that but driveability suffered.

Yeah, since there was no real control. Back then we had to play with fuel pressure, and clock the MAF and hope for the best.

 

[po-po 5.0]

Calibrated MAF's weren't perfect on an old EEC-IV, but it did serve it's purpose, when there was no real solution to properly recalibrate the PCM. WOT spark on the Fox body was a function of RPM, so calculated load was not nearly as important as it is today.

Certain companies continued to sell these "calibrated" MAFs WAY after the point where real solutions existed to properly recalibrate the PCM, though.

 

[Eric@HPTuners]

Certain companies continued to sell these "calibrated" MAFs WAY after the point where real solutions existed to properly recalibrate the PCM, though.

I agree, holding onto the past, I suppose.

 

[JesseSVTJames]

I agree, holding onto the past, I suppose.

Eric could you please PM me? I have a couple questions for you and dont want to jack this thread. I looked on your profile, PM isnt working and dont really want to leave a visitor message!

Thanks guys and sorry this is off topic, but seen the name and have been trying to contact for some while. :rockon:

 

[Eric@HPTuners]

Eric could you please PM me? I have a couple questions for you and dont want to jack this thread. I looked on your profile, PM isnt working and dont really want to leave a visitor message!

Thanks guys and sorry this is off topic, but seen the name and have been trying to contact for some while. :rockon:

For whatever reason, my PM's are disabled. You can email me via my Brooks Speed site.

 

[04cobradude]

You would be correct if it the fuel contained zero ethanol. On todays 10% ethanol blends it would be closer to 11.0. This is really why it is important to look at things in terms of lambda rather than afr. 11.0 on 10% ethanol fuel is pretty much the equivalent of 11.4 on pure gasoline. Looking at lambda puts everything on the same scale so you dont have to worry about the correction factors. Also, widebands are actually lamda sensors and they get hit with a multiplier to display afr. In order for the afr display to be correct, the multiplier used needs to be the same as the stoich point of the fuel being used.

you are partially correct... if you are tuning with a wideband that is calibrated on a gas scale, 11.4 is still 11.4... using a gas scaled wideband, you still tune e85 or e100 to GAS a/f ratios... the only difference is that it requires much more fuel to reach those proper targets..

if you were to use your logic, then stock NARROWBAND 02 sensors wouldnt work..

 

[04sleeper]

That's why I like to tune in Lambda.

 

[Eric@HPTuners]

you are partially correct... if you are tuning with a wideband that is calibrated on a gas scale, 11.4 is still 11.4... using a gas scaled wideband, you still tune e85 or e100 to GAS a/f ratios... the only difference is that it requires much more fuel to reach those proper targets..

if you were to use your logic, then stock NARROWBAND 02 sensors wouldnt work..

Bingo. Stoich seems to throw a lot of people off. I've seen other tuners posting about it incorrectly as the above poster did, and it makes me wonder...

 

[04cobradude]

That's why I like to tune in Lambda.

there really isnt a reason to tune in lambda unless that is just your preferred way... because MOST widebands on the market are set up for gas scale.. just my $.02 and i've had pretty good luck tuning about 500 e85 cars..

 

[po-po 5.0]

you are partially correct... if you are tuning with a wideband that is calibrated on a gas scale, 11.4 is still 11.4... using a gas scaled wideband, you still tune e85 or e100 to GAS a/f ratios... the only difference is that it requires much more fuel to reach those proper targets..

Interesting. I never even considered that.