Now that's a good question.

What can we measure? Resistance? However, you would have to measure that resistance at different air-flows as resistance with no airflow may not be representative. Hair dryer?! Airline with flow meter?
Air flow will make no difference without power to heat the wire.
 
Now that's a good question.

What can we measure? Resistance? However, you would have to measure that resistance at different air-flows as resistance with no airflow may not be representative. Hair dryer?! Airline with flow meter?
I just wondered if there was a static resistance that could be measured from the unit itself, there must be something way out of kilter on the new units as compared to the OEM ones as even trying to start the car is virtually impossible. It wouldn't be possible to get a reading from them even if the car did start due to backfiring and copious amounts of fuel being pumped in! As soon as you disconnect the plug to the MAF it then runs albeit a tad rough. The used OEM one I got runs fine and the car is a different beast! I don't want to remove the OEM one to get a reading just in case it upsets the old girl :) There must be a base line reading for the fru fru in the sensor for them to do QC
 
I just wondered if there was a static resistance that could be measured from the unit itself, there must be something way out of kilter on the new units as compared to the OEM ones as even trying to start the car is virtually impossible. It wouldn't be possible to get a reading from them even if the car did start due to backfiring and copious amounts of fuel being pumped in! As soon as you disconnect the plug to the MAF it then runs albeit a tad rough. The used OEM one I got runs fine and the car is a different beast! I don't want to remove the OEM one to get a reading just in case it upsets the old girl :) There must be a base line reading for the fru fru in the sensor for them to do QC
I have never had the opportunity to take a hot wire MAF apart, but in principle the hot wire is a variable resistance, the volt drop is measured to produce a signal proportional to airflow. Exactly what electronic parts are involved I do not know, but I doubt it is possible to measure the output without a test rig to apply power and airflow.
 
Pin-1 should be supply voltage. A1-6 connects via RL12 to 12V
Pin-2 will be the MAF output
Pin-3 goes back to the ECU Ground via A1-9.

Assuming no electronics inside the MAF, you should see static resistance across pins 2 & 3 (maybe 1-2 as well?). As Keith says you're not gonna see any change in output without power to it & airflow through.

GEMS & Thor as basically the same with different connector numbers.

1756456553881.png
 
Pin-1 should be supply voltage. A1-6 connects via RL12 to 12V
Pin-2 will be the MAF output
Pin-3 goes back to the ECU Ground via A1-9.

Assuming no electronics inside the MAF, you should see static resistance across pins 2 & 3 (maybe 1-2 as well?). As Keith says you're not gonna see any change in output without power to it & airflow through.

GEMS & Thor as basically the same with different connector numbers.

View attachment 348716
I have always assumed, perhaps incorrectly, that there would be electronics in the MAF, at the very least to compensate for the variations in input voltage.
 
I suspect you are correct Keith (hence why I said "assumed" above !! ).

Most docs are vague onb it, but "GEMS by Poole" document says this, but that could be a resistive divider with or without correction. Correction of non-linear output could easily be done in the ECU.


1756458137060.png
 
As above.

A wire heats up. That has a certain resistance. If that's wrong then you're already on a hiding to nothing. As air flows over the wire the wire cools and the resistance changes. However, if the expected change doesn't match what is expected because the wire is too thick / thin / different material then the car will either run rich or lean. That's why you would need to check the resistance with the wire hot and with a few different airflows.
 
I suspect you are correct Keith (hence why I said "assumed" above !! ).

Most docs are vague onb it, but "GEMS by Poole" document says this, but that could be a resistive divider with or without correction. Correction of non-linear output could easily be done in the ECU.


View attachment 348717
I think that more or less proves there are electronics involved. The supply is nominally 12 volts (12.8 to 14.8), output 0 to 5 volts. No way you can get reliably get zero volts from a basic resistance divider. As I say, I have never had one to check, but I suspect the MAF internals operate from a stable 5 volt supply obtained from the 12 volt input via a regulator. A 15% range of input voltage to the hot wire would cause wide variations in output.
 

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