MAF CAL is dedicated to making MAF calibration/MAF scaling a straightforward process
Calibrate signal from a MAF sensor which is mounted in a different/larger MAF housing.
MAF CAL by MoviChip
Fast & easy, wireless adjustment of calibration using Android device.
Permanent or temporary installation.
NOTE: This is a universal product. It may or may not be compatible with your engine setup. Read the product description to assess it’s suitability for your setup.
MAF CAL suitability Cheat Sheet
Background: The history of MAF CAL & how it’s tested and developed.
MAF CAL – Anticipated Uses
Setups where MAF signal is no longer accurate due to:
- Custom or aftermarket intake which uses a different or larger bore MAF housing
- Custom of aftermarket intake which relocates sensor position.
MAF CAL Usage Real-World Example – 1.8T 20V
Setup when engine mapped
VAG 1.8T 20v motor running a K04-064 turbo making circa 330bhp. When the engine was mapped it used a custom intake where the MAF sensor (Bosch HFM type) was located immediately after a 45 degree bend. Intake also used an aftermarket cotton type cone filter.
Issues
Short term fuel trims could sometimes max out at -25% at idle and in any case were around -20%.
MAF signal also appeared to be maxxing out at 4.4 volts at high RPM and high load.
MAF signal generally looked choppy on datalogs.
Remedies
Replacing the cotton air filter with a stock paper cone filter for an RS6 made a noticeable difference to the smoothness of the MAF signal.
Additionally relocating the MAF sensor directly after the air filter in a straight line also yielded a noticeable improvement in MAF signal quality.
Finally a larger MAF housing was used. Engine was mapped with a 70mm internal diameter housing, this was replaced with an 80mm internal diameter housing. This lowered the maximum MAF signal output from 4.4 volts down to around 3.8 volts. Idle and low load fuel trims improved massively but they were still slightly negative.
MAF Calibration
MAF CAL was used to reduce the MAF signal at idle and increase the signal at high load and high RPM.
Results
Fuel trims generally less than +/-5%.
Engine much smoother and with power delivery being more progressive. Fuel economy also improved.
When Might A Different/Larger MAF Housing Be Used?
Some examples
- Stock MAF housing is restrictive
- MAF sensor is at/close to the limit of what it can measure (larger housing increases flow measuring capability of the sensor)
- Aftermarket/custom intake system uses different MAF housing (length/shape/diameter)
- Original MAF housing too large (eg too long) to use with a custom intake system. There is insufficient space in engine bay to use the stock MAF housing.
- Engine mapped with an aftermarket intake which positioned MAF in a less than ideal position eg after a bend. After mapping MAF was relocated to get better flow signal quality.
MAF CAL – Key Features
- 11 adjustment points between 0 & 5 volts in 0.5 volt steps.
- +/-1% signal adjustment resolution at each point
- Adjustment percentage interpolated (linearly) between adjustment points
- Increase or decrease MAF sensor signal by up to +/-50% at each point
- Adjust MAF signal according to MAF signal only
- Fail safe bypass. If MAF CAL unit loses power, MAF CAL is bypassed & MAF sensor is connected directly to engine ECU.
IMPORTANT: Not compatible with frequency or SENT based MAF sensors. Only compatible with MAF sensors which output 0-5 volt analog signal.
When calibrating and/or scaling and/or adjusting the MAF sensor signal, a wideband lambda sensor should be used at all times to monitor the AFR.
MAF CAL – Key Benefits
- Dedicated to MAF scaling/calibration. No unnecessary features, easy to understand.
- Connects to car with as few as 4 wires
- Programmed through your existing Android phone/tablet. No small LCD displays, no scrolling through sub menus, no laptop required.
- Unit mounted in engine bay. No wires coming into cabin. Programmed wirelessly.
MAF CAL – Inputs & Outputs
12v Power (ACC) – Should be fused, 2 amp fuse.
Ground 12v
MAF In (0-5v) – Intercept
MAF Out (0-4.8v) – To engine ECU (max output 15 milliamps, 4.8 volts)
Load In (0-5v) – Tap (Optional. Connect to ground if unused)
12 Volt Out – Optional. External sensor power if required eg MAP (max current 0.5 amps). Use either 12v power or 5v power, not both.
Power Ground – Optional. External sensor. Connect Load In pin to this ground if load unused.
5 Volt Out – Optional. External sensor power if required eg MAP (max current 0.5 amps). Use either 12v power or 5v power, not both.
What’s Included
MAF CAL unit
MAF CAL Android app (downloaded from website)
MAF CAL unit connector, rubber boot and crimp connectors (user makes their own loom)
MAF CAL instruction manual (downloaded from the website)
Build sheet (contains details of components used, BT password and which app & manual to use)
What Else is Required?
Wires to construct loom & quality crimping tool
Essential: A method of constantly monitoring AFRs against MAF signal to protect engine.
Essential: A thorough understanding of the effects of adjusting MAF sensor signal on, for example, AFRs, ignition timing, traction control, boost control, EGTs and so on.
Essential: Multimeter for installation and trouble shooting.
Essential: A thorough understanding of the vehicle electrical and control systems which rely on MAF signal.
Why Use MAF CAL?
Depends on the type of lambda sensor used by engine ECU.
Wideband Lambda Equipped Cars
To reduce the short term fuel trim (STFT)/long term fuel trim (LTFT) corrections the ECU is making to achieve its target AFRs. (Where originally the trim corrections were acceptable but subsequently they became excessive due to changes in the engine intake and/or MAF placement and/or MAF piping).
Narrowband Lambda Equipped Cars
To achieve the target AFRs after a change to the intake system resulted in targets not being met.
In short, the purpose of MAF CAL is to compensate for any change which altered airflow through the MAF sensor since the current engine map was done.
What MAF CAL Cannot Do/Is Not Designed To Do
MAF CAL is not designed to compensate for a bad engine map and/or, to tune an engine.
It is intended to calibrate the MAF signal going to the ECU, so the ECU receives a more accurate picture of the amount of air actually entering the engine.
The assumption is the engine has an accurate/good engine map as a base point. But a modification was made to the MAF sensor (types of changes detailed above) where the air flow measured by the sensor no longer accurately represents the actual amount of air going into the engine. MAF CAL is intended to re-adjust this “corrupted” signal so the signal received by the engine ECU represents actual air flow.
How Does MAF CAL Adjust the MAF Signal?
MAF CAL uses an 11×1 2D map to adjust the MAF signal.
MAF signal correction is based on MAF signal input. For example at 2.5 volts input, the output signal can be increased by 5%.
MAF CAL does not adjust the MAF signal according to RPM, engine load etc.
MAF signal is adjusted according to the MAF signal only.
How is MAF CAL Programmed?
Using MAF CAL Android app which connects to main unit via Bluetooth. MAF CAL unit is designed to be mounted in the engine bay (away from heat, vibration and moisture) and is a fit and forget item.
MAF CAL vs Apexi SAFC/AFC Neo vs MoviChip MAF Manager – Differences
There are/were dedicated products available whose purpose was to tune the vehicle’s MAF sensor signal in order to tune the engine ie where current tune in the engine is not correct for the modifications (cams, injectors etc) done to the engine.
These products used load/TPS and RPM to alter MAF signal to get the desired air fuel ratio (and were intended for use on engines using a narrowband lambda sensor).
MAF CAL on the other hand is designed for engines which have a good engine map but where the intake has been changed in some way (as detailed above) leading to MAF sensor signal no longer giving the engine ECU and accurate picture of the amount of air entering the engine. MAF scaling restores accuracy to the MAF signal.
MAF Scaling – Why Reduce Amount of STFT/LTFT correction?
Why do we care about long/short term fuel trims?
Adjustment Window
There is a limit on how much the engine ECU can adjust fuel trims to achieve it’s target AFRs, for example it may be plus or minus 25%.
If the engine needs more adjustment than 25% then two things can happen. Either the engine will throw a check engine light and/or the fueling of the engine will not be correct.
By optimising the MAF sensor signal (reduce fuel trim adjustment to as close to zero as possible) we give the engine ECU the biggest possible adjustment window to get the AFRs where they need to be.
Ignition Timing
Assuming we are working from a good, correct map but the fuel trims are out because of some change in the intake, ignition timing may no longer be optimised (Ignition timing is dependent on the amount of air flowing into an engine at X RPM).
If the engine ECU is having to throw a lot of correction at the fuel trims because the MAF signal is not longer accurate, the ECU will use ignition timing for the amount of air it thinks is entering the engine.
For ignition timing to be optimal the engine ECU needs a MAF signal that truly represents the amount of air entering the engine. How much of an effect MAF signal has on ignition will depend on the ECU being used and how it is mapped.
MAF Scaling – IMPORTANT Proviso
When dealing with an out of spec/inaccurate/modified MAF sensor, there is one very important factor to consider.
The air passing through the MAF sensor must be as laminar as possible ie not turbulent.
Turbulent air is difficult, if not impossible to compensate for.
In turbulent air the flow measured by the MAF sensor will rarely/never be exactly the same even if engine state is the same. Flow must be consistent, for the MAF sensor to read mass air flow correctly.
If airflow through the MAF is inconsistent (datalog MAF signal to see) because the MAF sensor placement is bad, this problem needs to be eliminated before we start adjusting the MAF signal.
Causes of a Turbulent MAF Signal
- MAF sensor mounted on bend
- MAF sensor mounted close after bend, & within 20cm-30cm.
- Removal of air vanes/screen in MAF housing before MAF sensor. The guide vanes are there for a reason.
- Extreme heat. MAF sensors moved and mounted in area exposed to extreme heat.
- Moisture. Relocation to area where water spray/vapour can be pulled into sensor.
- Change of filter medium. Going from the stock paper type air filter to cotton/foam/metal mesh etc can affect accuracy of MAF signal when sensor mounted close to filter.
- Pipe diameter. Too large a diameter could lead to reversion through pipe/sensor at low flow rates.
- MAF housing material. If MAF housing changed to metal from plastic, sensor could be exposed to much higher temps.
Should You Use MAF CAL?
In a perfect world where the intake is not being changed regularly and you can change your engine map easily and/or cheaply, then ideally, the engine map will be changed directly without adding an external box like MAF CAL.
If you don’t want to take your car for a remap (to compensate for the MAF change or perhaps you are experimenting with different intake setups etc), then MAF CAL could be a good solution for you. It allows you to quickly and easily change the MAF sensor calibration, from your Android device.
BOV (Blow Off Valve) Assist
MAF CAL has an extra feature called BOV assist. It is designed for turbo charged cars using MAF and a BOV that vents to atmosphere.
-NOTE: We do not recommend using this function, you can read the reasons why here–
With the function turned on, when MAP reaches a certain level of vacuum, a fixed MAF voltage is sent to the engine ECU. The purpose being to prevent over fuelling between gearchanges.
Some Provisos
We recommend recirculating excess boost to the turbo inlet, post MAF. The eliminates the issue of overfuelling.
If venting to atmosphere, the BOV should be closed at idle. Which can cause issues.
In short, BOV Assist should be considered a band-aid and/or an experimental. It may or may not work for you. It is highly recommended to recirculate the air on MAF equipped engines. Recirculation has many benefits and none, if any downsides. The only possible “benefit” of venting to atmosphere is for sound purposes. But it is possible to get a lot of that sound even when recirculating. Check the BOV Assist article for more information.
Again, we do not recommend using this feature. Generally recirculating boost down stream of the MAF is the way to go, it has many benefits and no downsides that we know off. Read more information here.
MAF Scaling, MAF Tuning – Further Reading
MAF calibration using fuel trims
MAF Scaling
All articles related to MAF sensors
