What is the difference in actual maf sending units ie: 4.0 3.8 3.0 etc...
if I understand the sending unit, is interperted by a preset on the ecu?
following that thinking what are your thoughts? or am I totally wrong?

a2a a1a a1c aa a8 etc.

 

Each engine requires a different amount of air, obviously a 2.3L is going to require less air than a 3.0L which will require less than a 4.0L. Since it sends the signal to the ECU, the different MAFs are calibrated for different amounts of air. I think it just sends a "too little" or "too much" or "perfect" signal to the ECU, I don't think it sends like actual amounts the ECU interprets, therefore there is a difference in them.

 

From what I understand about MAF's (I'm used to 3 wire ones).
There are 3 lines, a regulated voltage power feed coming from the ECU (say +5V), ground, and an output signal that varies between 0-5V.

The MAF itself is calibrated such that at zero air flow, the output is 0V, at the max air flow, the output is +5V (some MAF's the output voltage is inverse to the air flow). There is a linear relationship between the output voltage and the air flow. The ECU has an A/D converter that converts the electrical signal (0-5V) into ADC counts ( for example 0 - 4095 for a 12 bit conversion) since the ECU computes using digital values and not analog ones.

The ECU is mapped to know that X ADC counts (or X volts) = Y air flow, along with other inputs it figures out how much fuel to supply and how much timing to set.

To maximize resolution, the voltage range should be as large as possible, or 0-5V output for 0-XXX cfm's. For example a MAF for a 1.6L motor will put out 0-5V output for 0-350CFM. A MAF for a 5.0L motor will put out 0-5V for 0 - 650CFM.

So generally you cannot swap MAF between cars without getting the ECU remapped since you'll get two different voltage outputs for the same CFM flow. The only way you can is if the MAF's are identical. Mfg's may do this if two different models of car's have similar displacements, or if the ECU has higher bits of resolution in the A/D conversion such that it can still get the dynamic range needed.

So the MAF does send the ECU a signal based on the MASS AIR FLOW, not just a "too little, too much" signal like a narrowband O2 sensor does, but you're also right that the ECU has presets - basically a lookup table (map) that allows it to know what the actual air flow is given a measured voltage.

Sorry if Ford isn't quite like this - I'm only a recent Ford owner.

 

Thank you both for your informative posts.

if you HAD to use a 3.8 maf on a 4.0 or a v8 maf on a 4.0 could you assume
that the 3.8 maf would run lean due to increased air flow and vice versa
for the v8. would there be any adverse conditions created?

 

so having no choice because i need my truck for work. I installed the 3.8

maf into my 4.0 drove city and highway and the truck runs great. got home

and put the code reader on and all clear all three modes.about 50 miles in

all. Is this long enough for the ecu to "learn"?

 

I don't believe the ECU will learn. That table of values, the voltage-air mass settings, is burnt into that ECU for good, it doesn't change, unlike shifting patterns for example that are relearned (which is why manuals are better ;-) )

 

The MAF's between those vehicles might be identical which is why it is working for you. If your MPG and smog tests are okay, then leave it in!

Don't know much about Ford ECU's to be able to tell you if they 'learn'. Someone else here might.

 

The ECU doesn't learn MAF amounts...I said that...

The values are close enough (3.8L / 4.0L) that they should interchange. I don't agree with doing it, that's beside the point though. The real test will indeed be in the longevity of the engine and the emissions testing.