MAF Sensor Position? (Turbo)
01-02-2009, 04:47 PM
#52
the temps take 30-60 sec to show cooler numbers (a slow, steady decline) when my car gets moving from when it was hot in the engine bay (before I had a CAI). The AIT sensor seems like it's extremely slow.
01-02-2009, 07:47 PM
#55
/\
Ok i 'm not sure on this but it appears to me like there are two sensors in the MAF
one measures air velocity (i think) and one measures temp . The two numbers enable the computer to work out mass air flow - it knows what dia. the tube should be so area is a constant.
The MAF is not one sensor - it is two sensors combined in one unit .
I'm picking the pressure sensor is included in that pcm calculation as well ....
bet you that if you took your remote temp sensor and put it in some cold water with the engine running your g/s readout would change ......
Ok i 'm not sure on this but it appears to me like there are two sensors in the MAF
one measures air velocity (i think) and one measures temp . The two numbers enable the computer to work out mass air flow - it knows what dia. the tube should be so area is a constant.
The MAF is not one sensor - it is two sensors combined in one unit .
I'm picking the pressure sensor is included in that pcm calculation as well ....
bet you that if you took your remote temp sensor and put it in some cold water with the engine running your g/s readout would change ......
Last edited by Brettus; 01-02-2009 at 07:57 PM.
01-02-2009, 07:58 PM
#56
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/\
Ok i 'm not sure on this but it appears to me like there are two sensors in the MAF
one measures air velocity (i think) and one measures temp . The two numbers enable the computer to work out mass air flow - it knows what dia. the tube should be so area is a constant.
The MAF is not one sensor - it is two sensors combined in one unit .
I'm picking the pressure sensor is included in that pcm calculation as well ....
bet you that if you took your remote temp sensor and put it in some cold water with the engine running your g/s readout would change ......
Ok i 'm not sure on this but it appears to me like there are two sensors in the MAF
one measures air velocity (i think) and one measures temp . The two numbers enable the computer to work out mass air flow - it knows what dia. the tube should be so area is a constant.
The MAF is not one sensor - it is two sensors combined in one unit .
I'm picking the pressure sensor is included in that pcm calculation as well ....
bet you that if you took your remote temp sensor and put it in some cold water with the engine running your g/s readout would change ......
^^not my words, i couldnt explain it that well...
01-02-2009, 08:04 PM
#58
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/\
Ok i 'm not sure on this but it appears to me like there are two sensors in the MAF
one measures air velocity (i think) and one measures temp . The two numbers enable the computer to work out mass air flow - it knows what dia. the tube should be so area is a constant.
The MAF is not one sensor - it is two sensors combined in one unit .
I'm picking the pressure sensor is included in that pcm calculation as well ....
bet you that if you took your remote temp sensor and put it in some cold water with the engine running your g/s readout would change ......
Ok i 'm not sure on this but it appears to me like there are two sensors in the MAF
one measures air velocity (i think) and one measures temp . The two numbers enable the computer to work out mass air flow - it knows what dia. the tube should be so area is a constant.
The MAF is not one sensor - it is two sensors combined in one unit .
I'm picking the pressure sensor is included in that pcm calculation as well ....
bet you that if you took your remote temp sensor and put it in some cold water with the engine running your g/s readout would change ......
the "hot wire" keeps constant temp by varying voltage. that required voltage correlates to a g/s point in the PCM. the hot wire will read correctly under any velocity or intake temp situations because thermal transfer is based on mass. the more air molecules you push across that wire, the more the wire is subjected to heat removal. the less molecules etc..... this should be totally independant of temp and velocity ...... i think
01-02-2009, 08:11 PM
#61
01-02-2009, 08:21 PM
#62
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Brettus, found some stuff explaining it a bit better... quoting pertinent stuff, rest is in the links. FWIW some details may not match up to our application as it appears the comes from Toyota tech talk, but the principles should be the same i think
Air flow sensors(hot wire MAF on first page) - http://www.autoshop101.com/forms/h34.pdf
Temp sensors(IAT about 2 pages in) - http://www.autoshop101.com/forms/h32.pdf
**** cant copy out of a PDF.....
Temp sensors(IAT about 2 pages in) - http://www.autoshop101.com/forms/h32.pdf
01-02-2009, 08:40 PM
#63
/\ excellent info there paul .
I can see how it works now . The role of the temp sensor is not entirely clear from that however . It helps with cold starts and is monitored by the pcm - but what the pcm does with this informatrion is not explained .....
I can see how it works now . The role of the temp sensor is not entirely clear from that however . It helps with cold starts and is monitored by the pcm - but what the pcm does with this informatrion is not explained .....
01-02-2009, 08:58 PM
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Air temperature affects density since colder air is more dense than warmer air. Many systems use an air temperature sensor to compensate for this factor since similar amounts of air can enter an engine at different temperatures. Some MAF sensors use an internal "cold" wire to send ambient temperature information to the computer. Some use an intake air temperature sensor in the manifold or the intake piping. This sensor is almost always ntc in design (negative temperature coefficient). That is, it's resistance goes up as air temperature goes down. This "thermistor" works just like a coolant temperature sensor and usually has identical resistance to temperature values.
http://www.kemparts.com/TechTalk/tt06.asp
01-02-2009, 09:16 PM
#66
Forgive me for skimming -
The temp sensor is for cranking correction and such, just like the BARO sensor.
If you flat those tables, the temp sensor doesn't affect the fueling.
Even when active, the IAT, BARO and CTS modify the load calculation, not fueling directly.
The MAF is completely self contained. It measures MASS, so temperature, density, velocity and pressure are all inferred directly from the one measurement.
The temp sensor is for cranking correction and such, just like the BARO sensor.
If you flat those tables, the temp sensor doesn't affect the fueling.
Even when active, the IAT, BARO and CTS modify the load calculation, not fueling directly.
The MAF is completely self contained. It measures MASS, so temperature, density, velocity and pressure are all inferred directly from the one measurement.
01-02-2009, 09:22 PM
#67
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EDIT:
THANK YOU, YOU FRIGGIN ANGEL! i was walking myself in circles trying to remember/relearn thermo.... because of density and a static volume, temperature and velocity basically make each other irrelevant. its all about the mass.
i think i may get it, but dont know how to explain it well....
here goes:
take it that i was wrong in assuming that heat transfer is purely mass related and not temp related.
if it IS temp related, then the PCM uses the IAT sensor as a kind of calibration gauge. because if temp matters, then 200g/s of 20C air wont cool the hot wire the same as 200g/s of 25C air....
heat transfer occurs via conduction...
this makes sense, less density means less molecules will be coming in physical contact with the hot wire...
so... hotter intake temps mean less dense intake air.. which means the hot wire doesnt react the same.... needs an ambient temp control to adjust for..
but ****... less dense air is still air...
200g/s at 5C might be a very dense charge moving at a slower velocity, and 200g/s at 30C is a less but given the fixed MAF tube volume, will be moving at a much higher velocity...
ultimately the velocity is not important, its the mass that matters...(for this)
ehhh i am leaving this thread for the night... too many things on my mind and i cant even follow basic thermodynamics right now... sorry if i confused anyone
Forgive me for skimming -
The temp sensor is for cranking correction and such, just like the BARO sensor.
If you flat those tables, the temp sensor doesn't affect the fueling.
Even when active, the IAT, BARO and CTS modify the load calculation, not fueling directly.
The MAF is completely self contained. It measures MASS, so temperature, density, velocity and pressure are all inferred directly from the one measurement.
The temp sensor is for cranking correction and such, just like the BARO sensor.
If you flat those tables, the temp sensor doesn't affect the fueling.
Even when active, the IAT, BARO and CTS modify the load calculation, not fueling directly.
The MAF is completely self contained. It measures MASS, so temperature, density, velocity and pressure are all inferred directly from the one measurement.
i think i may get it, but dont know how to explain it well....
here goes:
take it that i was wrong in assuming that heat transfer is purely mass related and not temp related.
if it IS temp related, then the PCM uses the IAT sensor as a kind of calibration gauge. because if temp matters, then 200g/s of 20C air wont cool the hot wire the same as 200g/s of 25C air....
heat transfer occurs via conduction...
As density decreases so does conduction. Therefore, fluids (and especially gases) are less conductive.
so... hotter intake temps mean less dense intake air.. which means the hot wire doesnt react the same.... needs an ambient temp control to adjust for..
but ****... less dense air is still air...
200g/s at 5C might be a very dense charge moving at a slower velocity, and 200g/s at 30C is a less but given the fixed MAF tube volume, will be moving at a much higher velocity...
ultimately the velocity is not important, its the mass that matters...(for this)
ehhh i am leaving this thread for the night... too many things on my mind and i cant even follow basic thermodynamics right now... sorry if i confused anyone
Last edited by paulmasoner; 01-02-2009 at 09:27 PM.
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