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/\ read back a few posts
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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.
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We were talking about mounting a different temp sensor before the throttle body post intercoler and leaving the air velocity sensor where it is ....
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Originally Posted by Brettus
(Post 2795783)
So : it stands to reason , if you measure velocity at one point and temp at a different point where the air is hotter - MAF will not be accurate .
It has NOTHING to do with the MAF. MAF = MASS airflow sensor. Temperature is already part of the equation. |
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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 ...... |
Originally Posted by Brettus
(Post 2796050)
/\
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... |
/\ maybe - why even have a temp sensor then ?
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Originally Posted by Brettus
(Post 2796050)
/\
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 |
Originally Posted by Brettus
(Post 2796066)
/\ maybe - why even have a temp sensor then ?
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I think i need to do an experiment to check if the temp sensor actually plays any role in the g/s calc done by the pcm .
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maybe it plays some part as a correction factor?? i'll do some reading and think about it, cause i've had this explained to me before(Kane) and i've dumped it all since :(
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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
shit cant copy out of a PDF..... Temp sensors(IAT about 2 pages in) - http://www.autoshop101.com/forms/h32.pdf |
/\ 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 ..... |
yeah i have been sitting here reading it the whole time trying to squeeze blood from that turnip...
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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 |
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. |
EDIT:
Originally Posted by MazdaManiac
(Post 2796133)
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. 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 shit... 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 |
I would have thought the Temp side was more of a correction for timing than fueling.
I mean once you know the MAS of air you can fuel accordingly - however if you have super heated air; timing should be retarded accordingly. |
Everything is based on load, which accommodates air, "super-heated" or not.
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