clutchman86

I was told that you can use a maf from an N/A on a TII my year model is an 88... IS this true???

NZConvertible

Firstly, FC's don't have MAF sensors, aka a hot-wire AFM. They have an older vane-type AFM.

NA and Turbo AFM's are calibrated differently to suit the engines' power. Using an NA AFM in a Turbo will cause the engine to run much richer all the time, and using a Turbo AFM in an NA will cause the engine to run much leaner all the time.

You can swap them for diagnostic purposes (i.e. to prove if the AFM is the cause of a problem or not) and the engine will run, but I would not drive the car with the wrong AFM installed.

Evil Aviator

... both of which are Mass Airf Flow (MAF) systems as per engineering terms.

I am a standalone EMS snob who does not know much about ghetto mods, but wouldn't a S-AFC compensate for the different vane calibrations?

stevej88na

Not to get bogged in technical terms, but I believe the vane-type is an AFM because it measures air flow, not air mass, while a hot-wire is a MAF, because it measures air mass, not air flow. You need to use other sensors, like temperature and pressure, along with the air flow measurement, to arrive at air mass with an AFM (I'll link to this project, even though I haven't worked on it in months). One might technically be a subclass of the other, but that's where the differentiation comes from. Also, I believe the N/A meter tops out at a lower air flow than the TII meter, so it's not simply a calibration issue, but measurement range as well. It could work short-term, but maybe not the best for long-term.

Evil Aviator

If you look more closely at the stock AFM you will see that it has two primary sensors; the vane and the temperature sensor. When combined as a unit this does measure mass airflow. The hot-wire type can also have a temperature sensor or a cold wire to act as a baseline reference. Also, as a minor correction to your statement, the hot-wire sensor measures mass airflow, not mass. Actually, it doesn't even measure this directly as the media hype would lead one to believe.

A pressure sensor is not required on an AFM or hot wire/film type system.

The AFM and MAF sensor are both components of a Mass Airflow system.

Common types of EMS:

1) Mass Airflow (MAF):
- AFM (Flapper type, cone type)
- MAF sensor (hot wire, hot film, cold wire)
- Vortex flow sensor (Karman)
2) Speed-Density
3) Alpha-N

The vane range shouldn't make much difference when a piggy-back fuel computer is used, although a wider range would allow for better tuning.

stevej88na

It seems to me that given a volume of air, you can't tell its mass without knowing its density:
mass = volume * density

For air, density changes with temperature and pressure:
mass = volume * (air pressure) / ((gas constant) * (air temperature))

So, to arrive at mass, you need to know the volume, pressure, and temperature of the air. As you said, the AFM covers two of these, with the flapper and the IAT, but the third component, pressure, requires the ATP (see training manual pages 4-40 and 4-41). Just as the IAT in the AFM correct about 20*C, the ATP corrects about 760mmHg.

Maybe you thought I meant a MAP sensor when I said pressure sensor, but I meant atmospheric pressure sensor - sorry for the ambiguity.

NZConvertible

Technically a vane AFM only measures air velocity, but because the cross-sectional area of the measuring point is fixed, the signal is proportional to volume flow. The air temp sensor in the AFM is needed so the ECU can calculate the mass airflow from the two signals. But I think you know all that. AFAIK the term MAF didn't even exist as an EFI-related term prior to hot-wire AFM's being used.

They're both "airflow meters". One is a vane AFM and the other is a hot-wire AFM, often referred to as a MAF sensor.