Hi all,

Various posts seem to indicate a good way to tune is to modify the MAF tables with the engine warm but in open loop. Unless there is modification to the MAF such as screens being removed etc, why should you have to do this?

If x amount of air passes over the wire then the MAF will output a certain voltage to represent that. Whether or not there's an engine attached to it ought to be irrelevant, the MAF is merely measuring air.

Having said all that, I decided to fiddle about with my MAF table #1 as I'm currently trying to get my engine to idle without it stinking. So, I jacked the back of the car up, hooked up a digital multimeter to the voltage output of the MAF and warmed up the engine. With the engine warm, I put the auto into drive and with my foot on the brake, pressed accelerator pedal until the voltage from the MAF became equal to each entry in MAF table #1, i.e .55V, 0.73V, 0.91V, 1.10V, 1.28V and 1.46V. I couldn't get an output as low as 0.37V.

When I had the MAF voltage on each value in the table I did some data logging and grabbed 300 or so samples. Then looking at the grams of air (not the raw value), I took the average and fed them back into the table. They were slightly higher for all of the defaults in an ARAP bin. It doesn't help my idle that I can tell but I think there are other issues going on - hopefully a WB will help when I get one.

I was surprised that I had to do this kind of calibration given I have a stock MAF sensor, so again I ask, why does this seem to be a necessary step?

 

Hot wire and film MAFs are a funny animal. Before I go further please understand that I can't cover or mention, or bring to the table all of the idiosyncrasies of the MAF. There are posts on them that cover a bunch of aspects.

A few points I recall are: a hot wire or film MAF will measure air-flow in both directions. So if there are pulses of air leaving the TB the MAF reports it (this causes a rich AFR and an increased load value).

The MAF report lags a change in angle of the TB blades. This change in angle is both opening and closing of the blades.

When using the MAF reported airflow for fueling calculations it doesn't take into account the engine load. The ECM calculates load from the airflow and RPM, which affects spark advance. But it isn't used for fueling.

Which also means that re-calibrating the MAF tables also changes the SA. Due to a different load being calculated (LV8 & LV16).

A change in SA also affects the apparent AFR. So tuning becomes circular.

The reported MAF airflow is affected by the ductwork prior to and after the MAF.

Basically in the end the tuner changes the MAF tables/scalars to suit the setup. Once the MAF tables are setup they do hold the tune. There are some decent threads on MAF tunes. Some got heated, but ignore the chaff and look for the wheat.

RBob.

 

Woah, this gets heavy quite quicky doesn't it?

Is the method I used to calibrate the MAF a good one? After which I forget about changing it any further and get onto playing with fuel and SA?

 

How you loaded the engine is OK for the lower end. Where I got confused is what you did with the gms/sec and voltage readings. Then fed these back into the MAF tables.

To do this in open loop a WB is required. Can also do this in closed loop by logging the BLM values. This is done by driving around. Hold the go-pedal steady to allow time for the BLM to stabilze. This will provide the best data.

For the lower end where the injector PW is small you may need to change the injector compensation tables. There are two: by voltage, and by PW.

RBob.