MAF calibration unable in closed loop

Hi All,

Regarding MAF-scaling, the particular ECU on my car (or the mappack) does not have a MAF-sensor output voltage table, all I´m able to edit are load tables named "Mass air flow". During datalogging my fuel trims are just fine, but just for learning I did edit some of the numbers in that table, in order to simulate correcting the MAF-scaling. But the numbers did not affect closed loop, only open loop.

Is this normal? This basicly means, that on this car I´m not able to adjust the MAF-calibration in closed loop.

In general I think I´m a little confused about the MAF-scaling. Not why it needs to be done, but more the tables it needs to be done in.

Hope for some help again :)

/Simon

MAF scaling is needed to tell the ECU precisely how much air is available at the current condition. This would be used when in open loop mode, depending on the ECU, it may be used as a starting point for closed loop operation, but of course the closed loop control will modify the airflow (by adding short term fuel trims) used for calculating the amount of fuel to inject to achieve the target mixture.

So it's important to tune the MAF output (scaling) so that the closed loop system has less to do (i.e. the short term fuel trims remain low).

You also need to realize that every ECU / Platform may have slightly different names for the table that takes a voltage or frequency from the MAF sensor and determines how much air mass is entering the engine. Some tables the axis as voltage or frequency, and the output is air mass, and some have the axis as airmass, and entries in the table are the voltage or frequency that produces that air mass.

To get more specific help, you probably need to provide details on the ECU (or if factory, then what brand / model / year the engine is), and what tools you are using for reflashing. If we aren't familar with that, then you might need to provide some screen shots showing the tables you think are related to the MAF (calibration, translation, scaling).

HI David,

Thanks for your anwser! But if the ECU does not use the MAF-sensor to calculate the correct fuel amount in closed loop, which data does it then use in closed loop? It at least needs some fixed tables of air flow to calculate the correct amount of fuel, if the MAF-sensor signal is disregarded.

I'm just getting started after going through the courses of reflashing, so I'm just using my own car as practice. Basicly going through the 6-step process. The MAF-scaling part is what confuses me, as you can read :)

I really apreaciate your help!

/Simon

Not a lot of information to go off,

But in closed loop your narrowband O2 sensors will "fix" any error in the MAF table - "Your Job" Is to minimise that error. in open loop your narrow band O2s are doing nothing, hence why you might be seeing your AFR/Lamda changing with your changes

Are you noticing that your "Short Term / Long Term" Fuel trims are changing with your experiment?

EG if you LTFT is at +2 , Then you make a change of say +5% it should be around a +7% in that cell in *closed loop*

In open loop your Wideband will show the error.

Hi Brock,

Thanks for your anwser, but I am aware of how the open- and closed loop works in order to balance the afr. What confuses me (and I know it proberly varies depending on what ECU you´re working on) is when the MAF-sensor is decoupled from the ECU, eg. in closed- or open loop. This makes a difficult for me to calibrate it, if I don´t know when it is operating. I thoght it was enabled when driving in closed loop.

In this particular case (my car) there is a wide band O2 sensor pre cat, and a narrow band post cat. The mappack for my ECU have 8 maps related to mass air flow, but only four of them makes sense to me (marked with a blue line), because I confirmed via datalogging that those numbers in the table match real world. Those four maps are load maps with rpm on the y-axis and load on the x-axis, with mass air flow in kg/h. See attached.

The other four mass air flow maps (which are below the just mentioned four) I can´t make sense of, the numbers in the table don´t match anything which I am aware of.

So I guess my question still is, if the MAF-sensor is disabled in closed loop, where does the ECU then get the mass air flow from in order to calculate the fuel delivery (eg.14,7/1 afr) ?

Is it the right approach when calibrating the MAF-sensor, that I edit the numbers in the load table (the one I spoke of in blue) depending on the fuel trims of course?

It would take research to understand how YOUR ECU works, and understanding how it uses open/closed loop - im unfamiliar with what youre working with but there is generally a "failsafe" system that will active if the MAF Fails or if your ecu has a dynamic airflow system.

For Example: GM Vehicles have a Speed Density system that (If the maf is failed, or RPM is above a setpoint) will use the MAP Sensor and RPM to create a 3D Load Axis, without knowing the vehicle or having a tune file, its hard to help understand how your system functions.