Datatek
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Air flow will make no difference without power to heat the wire.
P38A MAF woes
- Thread starter cornishboater
- Start date
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Grrrrrr
Technician, Bodgit & Scarper Ltd
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That's true. You think the wire failed? I wonder if one of those thermometers you point could pick it heating up?
Datatek
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I doubt the wire has failed, more likely a bad connection on the pcb or component failure
cornishboater
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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
Datatek
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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.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
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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.
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.
Datatek
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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.
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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.
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.
Grrrrrr
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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.
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.
