Calibrating The Maf Sensor

[Krambo]

GM uses a Hot Wire MAF design which is similar to a hot wire anemometer used in industry to measure air volume flow in air handlers and laboratory instrumentation. The air mass measurement is achieved by heating a wire with an electric current that is suspended in the engine’s air intake stream. The wire's electrical resistance increases as the wire’s temperature increases, which limits electrical current flowing through the circuit. When air flows past the wire the wire cools, decreasing its resistance, which in turn allows more current to flow through the circuit. As more current flows, the wire’s temperature increases until the resistance reaches equilibrium again. The amount of current required to maintain the wire’s temperature is directly proportional to the amount of air flowing past the wire. The integrated electronic circuit converts the measurement of current into a frequency signal (Hz) which is polled by the PCM. If air density increases due to pressure increase or temperature drop, but the air volume remains constant, the denser air will remove more heat from the wire indicating a higher mass airflow.

 

Now that we have a basic understanding how the MAF measures the incoming air flow, how does the PCM use this info? The PCM receives the airflow signal from the MAF (in Hz, i.e. frequency) and references a table to “look-up” a corresponding airflow value (in g/sec). This airflow value is used to calculate final air mass in g/cyl using RPM and the amount of cylinders of the engine which ultimately act as inputs for fueling calculations. If this table is incorrectly calibrated, the commanded fueling will not equal the actual Air Fuel Ratio, among other items.

 

GM comes up with their MAF transfer function (calibration) on a flow bench not an engine and an intake system from what I have read in technical journals and the trustworthy internet blogs. This is great however when the MAF is installed on various aftermarket CAI systems, de-screened, ported etc, this calibration changes. It is then up to the tuner to correct the calibration while on the engine. Here is one way to do it:

 

NOTE: This is ONE approach to calibrating the MAF. There are a couple of ways to do it that ultimately end up with good results. Just like Ve table tuning, some like to use a wideband only, some STFT, some a combo. This write-up is written so some of the people with only basic tuning equipment (HPT standard and no wideband) can benefit. If you have been thinking of replacing your stock, old O2 sensors, now is the time as crappy sensors will only build an incorrect bias into your calibration. It is also a good idea to clean the MAF sensor with an approved method / solvent and to fill up your fuel tank with the fuel you will be using. Varying ethanol contents of today’s fuel will impact the final result so by filling up and completing your tuning within one tank ensures little bias. The use of a wideband is the only way to calibrate the upper end of the MAF table. I take no responsibility if you screw up your tune and damage your motor!

 

The following is assuming that your fixed variables (IFR, Engine Volume etc.) are correct and your Ve was already dialed in. Also this assumes that the fuel you are using is Ethanol free or otherwise your STOICH value is adjusted to compensate for the % ethanol blend you are using. “Read Entire” your current tune file and save it in a safe location. Now do the following:

 

1. Set the Dynamic Airflow High RPM Disable to ZERO. HPT > Engine > Airflow > Dynamic Airflow > Hi RPM Disable. This will throw your tune into a MAF only tune and ignore the Ve Table for fueling calculations.

 

2. Disable DFCO by setting DFCO enable temp to 284*. HPT > Engine > Fuel Control > Fuel Cutoff > Deceleration Fuel Cut-off > Enable Temperature.

 

3. Disable COT HPT > Engine > Fuel Control > COT Lean Cruise > COT to DISABLE.

 

4. Disable LTFT by setting the LTFT minimum Enable ECT to 284*. HPT > Engine > Fuel Control > OL&CL > LTFT Enable > Min ECT.

 

5. Copy your Hi Octane timing table to your Lo Octane timing table.

 

Save this tune with the changes above as MAF-1 or something OTHER THAN your current tune. Do not overwrite your current saved tune! - very important as you will want to cut and paste the tuned MAF table back into this tune once all is done. Now flash (write calibration only) this tune (MAF-1) to your truck.

 

Set up your VCM Scanner:

 

You can use this configuration posted in the HPT configuration repository or you can build your own. I actually used the one posted in the HPT forum and modified some of the histograms to my desires. For this logging session, use histogram #4 (tell you why later).

 

MAF tuning LTFT.cfg

 

Start your truck and get your O2 sensors hot. Using the VCM controls in the scanner, reset your fuel trims! I always do this out of habit and for good reason as if you have any stored LTFT’s, they will impact the final calibration.

 

Start logging while looking at histogram 4 in the COUNT mode. So by that, click on the big capital C in the toolbar (next to the “L”). The goal will be to obtain 150 counts in each cell (typical range you will see hits will be from 3000 - 8000 Hz). Now, drive normally with nice slow acceleration . To hit some of the higher cells, put the truck in 2nd gear. For the higher cells, you may notice that the logging suddenly stops. This is because there is a filter built into this histogram to filter out any Pe numbers. This is very handy as all you need to do is just drive smoothly and obtain whatever cells you can. Once you have at least 150 hits in the cells you can hit, stop the log and “save data as”. I usually save this as MAF-1.

 

Now that the data is saved, click on the “A” which will now display the average for each cell. The numbers you see here are the “percent” off from your commanded STOICH value in your tune (usually 14.68x for gasoline), either rich (negative values) or lean (positive values). Highlight the entire table in histogram 4, ensuring that you are in “Average” display and right click, copy. Open your MAF-1 working tune (the one you flashed to do this log) and go to Engine > Airflow > General Airflow > MAF Calibration, Airflow vs. Frequency and highlight the entire table. Now right click on the table, select Paste Special, multiply by % - half. What this just did was correct your MAF calibration by 50% of the values you just scanned. Personally, I click on the smooth selection button one time here, save the tune and reflash into the truck. Repeat the logging process with the cut / past special multiply by % half into the MAF working tune until all of the cells you are logging are within +/-0.75% of zero or tighter. When all values are within the goal of 0.75%, congratulations, you calibrated your non-Pe section of your MAF table using STFT and your narrow band 02 sensors.

 

Now that you calibrated the non-Pe portion of the MAF table, you can click on the 2D view of the MAF Airflow vs. Frequency table in your working MAF tune and look at the curve. You will see that the curve wants to go in in a certain direction compared to your stock calibration, often 10% leaner than stock but not always. What I do is click on the line and manually drag the curve (manual interpolation). This is optional but it helps get the job done quicker for the next step. If you do not have a wideband, this is as far as you can go anyway. You do not want a shelf where the new calibrated data stops and the stock Pe portion of the curve starts so smoothing the curve is a good idea. Flash the tune into the truck in prep for the WOT calibration. If you will NOT be doing the WOT cal, copy the new MAF calibration into your starting tune that you did not to write over and flash back into your truck.

 

WOT MAF calibration using a wideband:

 

Using the same configuration, you must add your wideband to the Table View portion of the scanner. Not going to get into how to do this, so reference the HPT forum for assistance or use the HELP feature of the scanner. So now that the wideband is hooked up to the scanner, you will be using Histogram 6 in the same scanner configuration. Ensure the MAF-1 tune (with the new MAF table you worked on above) is flashed into your truck, fire up the truck, clear the fuel trims and begin logging. Looking at histogram 6, you will only see values when you go into Pe Mode (WOT) so this will obviously require some WOT pulls to get the data necessary (this histogram is also filtered, for anything

 

This is a screen shot of 4 calibration sessions that have been laid over each other for illustration purposes. This view is histogram 6 with the initial run on the bottom. After working through 3 additional sessions (looking from the bottom up), you can see the improvement. I focused on the 9500 cell on up as lower than 9500 is just noise induced by flashing the converter and a small bit of tire spin. I did not use any values below 9500 because of that. Your sessions will vary on what cells to look at. You will be able to determine that once you get going:

 

 

When complete, copy your entire calibrated MAF Airflow vs. Frequency table from your MAF tune back into your initial tune that you made sure to not overwrite earlier. Flash this tune and enjoy your calibrated MAF table! You will now be able to command a Pe value and actually see that value on your Wideband which makes the fuel tuning that much easier.

 

For me, I like to do both the non-Pe portion of the MAF table and the Pe portion altogether using % AFR error and my wideband. Not only does it save time but also avoids variability in the narrowband sensors. Again, the above was written so that people without a wideband can do at least some calibration.

 

For those of you that are familiar with calibrating the MAF, please correct wherever I may have misspoken or add your input. The intent of this write-up is to coach others on how to make the most out of their investments!

Edited April 25, 2010 by Krambo (see edit history)

[chpspecial]

Very good write up as always Kevin...

 

[12'SROCK]

Great info Kevin

[chpspecial]

GM uses a Hot Wire MAF design which is similar to a hot wire anemometer used in industry to measure air volume flow in air handlers and laboratory instrumentation. The air mass measurement is achieved by heating a wire with an electric current that is suspended in the engine’s air intake stream. The wire's electrical resistance increases as the wire’s temperature increases, which limits electrical current flowing through the circuit. When air flows past the wire the wire cools, decreasing its resistance, which in turn allows more current to flow through the circuit. As more current flows, the wire’s temperature increases until the resistance reaches equilibrium again. The amount of current required to maintain the wire’s temperature is directly proportional to the amount of air flowing past the wire. The integrated electronic circuit converts the measurement of current into a frequency signal (Hz) which is polled by the PCM. If air density increases due to pressure increase or temperature drop, but the air volume remains constant, the denser air will remove more heat from the wire indicating a higher mass airflow.

 

Now that we have a basic understanding how the MAF measures the incoming air flow, how does the PCM use this info? The PCM receives the airflow signal from the MAF (in Hz, i.e. frequency) and references a table to “look-up” a corresponding airflow value (in g/sec). This airflow value is used to calculate final air mass in g/cyl using RPM and the amount of cylinders of the engine which ultimately act as inputs for fueling calculations. If this table is incorrectly calibrated, the commanded fueling will not equal the actual Air Fuel Ratio, among other items.

 

GM comes up with their MAF transfer function (calibration) on a flow bench not an engine and an intake system from what I have read in technical journals and the trustworthy internet blogs. This is great however when the MAF is installed on various aftermarket CAI systems, de-screened, ported etc, this calibration changes. It is then up to the tuner to correct the calibration while on the engine. Here is one way to do it:

 

NOTE: This is ONE approach to calibrating the MAF. There are a couple of ways to do it that ultimately end up with good results. Just like Ve table tuning, some like to use a wideband only, some STFT, some a combo. This write-up is written so some of the people with only basic tuning equipment (HPT standard and no wideband) can benefit. If you have been thinking of replacing your stock, old O2 sensors, now is the time as crappy sensors will only build an incorrect bias into your calibration. It is also a good idea to clean the MAF sensor with an approved method / solvent and to fill up your fuel tank with the fuel you will be using. Varying ethanol contents of today’s fuel will impact the final result so by filling up and completing your tuning within one tank ensures little bias. The use of a wideband is the only way to calibrate the upper end of the MAF table. I take no responsibility if you screw up your tune and damage your motor!

 

The following is assuming that your fixed variables (IFR, Engine Volume etc.) are correct and your Ve was already dialed in. Also this assumes that the fuel you are using is Ethanol free or otherwise your STOICH value is adjusted to compensate for the % ethanol blend you are using. “Read Entire” your current tune file and save it in a safe location. Now do the following:

 

1. Set the Dynamic Airflow High RPM Disable to ZERO. HPT > Engine > Airflow > Dynamic Airflow > Hi RPM Disable. This will throw your tune into a MAF only tune and ignore the Ve Table for fueling calculations. EFI table I can't find this table on EFILive..

 

2. Disable DFCO by setting DFCO enable temp to 284*. HPT > Engine > Fuel Control > Fuel Cutoff > Deceleration Fuel Cut-off > Enable Temperature. EFI table B3313, B3315

 

3. Disable COT HPT > Engine > Fuel Control > COT Lean Cruise > COT to DISABLE. EFI table B4205

 

4. Disable LTFT by setting the LTFT minimum Enable ECT to 284*. HPT > Engine > Fuel Control > OL&CL > LTFT Enable > Min ECT. EFI table B3801 to enable/disable, B 3802 to use engine temp

 

5. Copy your Hi Octane timing table to your Lo Octane timing table. EFI table B5913 to B5914

 

Save this tune with the changes above as MAF-1 or something OTHER THAN your current tune. Do not overwrite your current saved tune! - very important as you will want to cut and paste the tuned MAF table back into this tune once all is done. Now flash (write calibration only) this tune (MAF-1) to your truck.

 

Set up your VCM Scanner:

 

You can use this configuration posted in the HPT configuration repository or you can build your own. I actually used the one posted in the HPT forum and modified some of the histograms to my desires. For this logging session, use histogram #4 (tell you why later).

 

MAF tuning LTFT.cfg

 

Start your truck and get your O2 sensors hot. Using the VCM controls in the scanner, reset your fuel trims! I always do this out of habit and for good reason as if you have any stored LTFT’s, they will impact the final calibration.

 

Start logging while looking at histogram 4 in the COUNT mode. So by that, click on the big capital C in the toolbar (next to the “L”). The goal will be to obtain 150 counts in each cell (typical range you will see hits will be from 3000 - 8000 Hz). Now, drive normally with nice slow acceleration . To hit some of the higher cells, put the truck in 2nd gear. For the higher cells, you may notice that the logging suddenly stops. This is because there is a filter built into this histogram to filter out any Pe numbers. This is very handy as all you need to do is just drive smoothly and obtain whatever cells you can. Once you have at least 150 hits in the cells you can hit, stop the log and “save data as”. I usually save this as MAF-1.

 

Now that the data is saved, click on the “A” which will now display the average for each cell. The numbers you see here are the “percent” off from your commanded STOICH value in your tune (usually 14.68x for gasoline), either rich (negative values) or lean (positive values). Highlight the entire table in histogram 4, ensuring that you are in “Average” display and right click, copy. Open your MAF-1 working tune (the one you flashed to do this log) and go to Engine > Airflow > General Airflow > MAF Calibration, Airflow vs. Frequency and highlight the entire table. Now right click on the table, select Paste Special, multiply by % - half. What this just did was correct your MAF calibration by 50% of the values you just scanned. Personally, I click on the smooth selection button one time here, save the tune and reflash into the truck. Repeat the logging process with the cut / past special multiply by % half into the MAF working tune until all of the cells you are logging are within +/-0.75% of zero or tighter. When all values are within the goal of 0.75%, congratulations, you calibrated your non-Pe section of your MAF table using STFT and your narrow band 02 sensors.

 

Now that you calibrated the non-Pe portion of the MAF table, you can click on the 2D view of the MAF Airflow vs. Frequency table in your working MAF tune and look at the curve. You will see that the curve wants to go in in a certain direction compared to your stock calibration, often 10% leaner than stock but not always. What I do is click on the line and manually drag the curve (manual interpolation). This is optional but it helps get the job done quicker for the next step. If you do not have a wideband, this is as far as you can go anyway. You do not want a shelf where the new calibrated data stops and the stock Pe portion of the curve starts so smoothing the curve is a good idea. Flash the tune into the truck in prep for the WOT calibration. If you will NOT be doing the WOT cal, copy the new MAF calibration into your starting tune that you did not to write over and flash back into your truck.

 

WOT MAF calibration using a wideband:

 

Using the same configuration, you must add your wideband to the Table View portion of the scanner. Not going to get into how to do this, so reference the HPT forum for assistance or use the HELP feature of the scanner. So now that the wideband is hooked up to the scanner, you will be using Histogram 6 in the same scanner configuration. Ensure the MAF-1 tune (with the new MAF table you worked on above) is flashed into your truck, fire up the truck, clear the fuel trims and begin logging. Looking at histogram 6, you will only see values when you go into Pe Mode (WOT) so this will obviously require some WOT pulls to get the data necessary (this histogram is also filtered, for anything

 

This is a screen shot of 4 calibration sessions that have been laid over each other for illustration purposes. This view is histogram 6 with the initial run on the bottom. After working through 3 additional sessions (looking from the bottom up), you can see the improvement. I focused on the 9500 cell on up as lower than 9500 is just noise induced by flashing the converter and a small bit of tire spin. I did not use any values below 9500 because of that. Your sessions will vary on what cells to look at. You will be able to determine that once you get going:

 

 

When complete, copy your entire calibrated MAF Airflow vs. Frequency table from your MAF tune back into your initial tune that you made sure to not overwrite earlier. Flash this tune and enjoy your calibrated MAF table! You will now be able to command a Pe value and actually see that value on your Wideband which makes the fuel tuning that much easier.

 

For me, I like to do both the non-Pe portion of the MAF table and the Pe portion altogether using % AFR error and my wideband. Not only does it save time but also avoids variability in the narrowband sensors. Again, the above was written so that people without a wideband can do at least some calibration.

 

For those of you that are familiar with calibrating the MAF, please correct wherever I may have misspoken or add your input. The intent of this write-up is to coach others on how to make the most out of their investments!

 

 

Kevin, maybe you can add the stuff in red to help out the people using EFILive

[Krambo]

Kevin, maybe you can add the stuff in red to help out the people using EFILive

 

 

You just did! Thanks for adding input.

[MR.364SS]

You just did! Thanks for adding input.

 

 

hey guys i need some much needed help for some reason my truck started this pulsing thing in the dash bord and the lighting inside the truck, im trying to figure what it could be i changed the altinator and its still doing it i checked the batter and its fine. i also tryed taking of the power wire that comes from the altinator and it went away then i put it back on and it came back.

 

so if any body know what im talking about or might have any ideas please help haha

 

 

 

 

mr.364ss

[PHALERYDR]

hey guys i need some much needed help for some reason my truck started this pulsing thing in the dash bord and the lighting inside the truck, im trying to figure what it could be i changed the altinator and its still doing it i checked the batter and its fine. i also tryed taking of the power wire that comes from the altinator and it went away then i put it back on and it came back.

 

so if any body know what im talking about or might have any ideas please help haha

 

 

 

 

mr.364ss

I know this is an old post but My 04 is doing the same thing.