# maf sensor



## sentraspeed (Mar 26, 2003)

so i am trying to get this all right...is it possible to mount the maf before the turbo so it dosent see boost and wouldnt go crazy? would that mess with the computer and fuel? thankx alot


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## wes (Apr 30, 2002)

sentraspeed said:


> so i am trying to get this all right...is it possible to mount the maf before the turbo so it dosent see boost and wouldnt go crazy? would that mess with the computer and fuel? thankx alot


The MAF HAS to be mounted before the turbo on our cars.


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## sentraspeed (Mar 26, 2003)

i thought that the maf was located in the same spot it always is? im confused at the moment


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## sentraspeed (Mar 26, 2003)

never mind i just took a new look at the mikes and saw that it was moved...so whats the point of upgrading the maf? air flow? or does the boost actually still throw it out of wack?


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## Stephen Max (Aug 18, 2003)

wes said:


> The MAF HAS to be mounted before the turbo on our cars.


Why is that? I have wondered about this for a while and have come to no real conclusion on my own.


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## chimmike (Oct 17, 2002)

what happens to your MAF when it sees a tiny bit of turbulence? it goes 'oh shit! all hell is breaking loose!'

Imagine the MAF seeing compressed, high velocity air. It'd be saying "holy hell I'm gonna just shut down now"


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## Stephen Max (Aug 18, 2003)

chimmike said:


> what happens to your MAF when it sees a tiny bit of turbulence? it goes 'oh shit! all hell is breaking loose!'
> 
> Imagine the MAF seeing compressed, high velocity air. It'd be saying "holy hell I'm gonna just shut down now"


The air velocity is going to be the same in front of the blower as it is after the blower in steady state conditions (i.e. constant boost pressure). 

Is the air any more turbulent because of boost pressure? I would not have thought so, but I guess passing through a blower is going to disturb it.

The reason I ask is that there are plenty of supercharged Maximas running around with mafs after the blower with no driveability problems, but the turbo people always insist on the maf before the blower. I never have understood that.


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## NotAnotherHonda (Aug 7, 2003)

hey sentra speed, i like your sig haha


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## mcr (Jan 22, 2004)

Stephen Max said:


> The air velocity is going to be the same in front of the blower as it is after the blower in steady state conditions (i.e. constant boost pressure).
> 
> Is the air any more turbulent because of boost pressure? I would not have thought so, but I guess passing through a blower is going to disturb it.
> 
> The reason I ask is that there are plenty of supercharged Maximas running around with mafs after the blower with no driveability problems, but the turbo people always insist on the maf before the blower. I never have understood that.


My guess is that since the MAF is just a hot wire anemometer it is going to be more accurate with air at ambient termperature. Intercoolers notwithstanding, the compressed air is going to be hot thus fooling the MAF into thinking not as much air has gone by. If more air has been injested than the ECU thinks, then a lean condition will result.

- Mike


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## dave_f (Dec 11, 2002)

locating the MAF before the turbo will help it live longer. Some cars run this setup (no cars that I know of are produced from the factory this way) because of space and plumbing constraints. There is a possibility of oil getting into the intake track and really screwing up the sensor. The source of oil can be come from either the breather lines or turbo seals. without the presence of oil, a properly installed MAF sensor will read the same value before or after the turbo regardless of pressure or temperature. This is because a Mass air flow sensor does just that, it measures the Mass Flow... if the pressure is boosted up, more air molecules will pass across the wire and help cool the wire better, the sensor will account for the increased air. If the charge air is heated up, it will cool the wire less ... the MAF will know exactly how many molecules are passing thru it. That's why many MAF cars don't have intake temp sensors or barometric sensors... the MAF automatically compensates. Its hard to fool the sensor unless you create turbulence thru the sampling section of the MAF.
-dave



mcr said:


> My guess is that since the MAF is just a hot wire anemometer it is going to be more accurate with air at ambient termperature. Intercoolers notwithstanding, the compressed air is going to be hot thus fooling the MAF into thinking not as much air has gone by. If more air has been injested than the ECU thinks, then a lean condition will result.
> 
> - Mike


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## Stephen Max (Aug 18, 2003)

Thanks, Dave, that was very informative. 

I have also heard that an acoustic resonance in the intake tract can cause faulty maf readings. The theory is that if the air pressure is oscillating back and forth as it passes through, then the maf will read the air twice. I would think the average value would be the same, though, since the air is moving slower than average speed just as much as when it is moving faster than average. I log my maf voltage with a datalogger, and I have indeed noticed an oscillating voltage, but only after closing the throttle at high rpm when the air is escaping through the bov (which I have placed before the maf). It doesn't seem to happen at WOT with the rpms climbing.

Concerning oil on the sensor. Will a chemical degreasing spray do any damage to the sensor? I know there are several electrical contact cleaning sprays on the market and I'm considering using one.


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## koroshiya (Dec 28, 2002)

Stephen Max said:


> Concerning oil on the sensor. Will a chemical degreasing spray do any damage to the sensor? I know there are several electrical contact cleaning sprays on the market and I'm considering using one.



I don't know about the long term effects, but i had oil in my intake from the head(faulty PCV) i just ran the engine to about 3K rpm, then sprayed carb/tb cleaner. cleaned it out real good, had black smoke for about 10mins then went clean, also ad a CEL for a few days after that, but went away on it's own. No problems since then, about 3 weeks ago and still working good.

As i said i don't know the long term affects of doing this, but it fixed my imediate probs, maybe others can comment.

Dave


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