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Relocated Afm Now Idles High

sirdriftsalot

By sirdriftsalot,
in Engines & Forced Induction

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GTSBoy Grand Master

GTSBoy

Posted
Posted

Are you surprised by this? You have drastically changed the installation location of a rather sensitive hot wire anemometer, and as a result it now reads a (possibly slightly, possibly drastically) different air flow velocity at idle, and you haven't retuned your ECU to cope?

kitto Mentor

kitto

Posted
Posted

Of course it will be fine before the relocation.

When you move the AFM into the pressure side change what the AFM reads and therefore the scaling must be changed with a retune.

Read what GTSboy said again.

Dose Pipe Sutututu Grand Master

Dose Pipe Sutututu

Posted
Posted

Was fine before the afm relo, but could re locating cause what I've mentioned?

Because I didn't touch any vac lines except for boost tee, but seems fine now as I've returned it back to standard

Cheers

Of course, air flows different and is more dense.. the ECU would be reading differently. Pre turbo, air is less dense, if you like the noise I would just go a MAP based sensor ECU and drop the AFM totally, then you can install a DOSEEEEEE pipe and sound like a VL... suuuuuu tututu LOL

GTSBoy Grand Master

GTSBoy

Posted
Posted

It's not the density. These AFMs are MASS air flow meters remember. They don't care what the density is. Well actually, they do care a little tiny bit, but not enough to worry about. What they do care about is that the entry conditions are completely different. Stock location it is pulling from a relatively open box. In a pipe, it is pulling from a pipe. The air flow pattern that is in place atr the sensing element is different. So whilst the sensor might see X condition in both locations and therefore output Y volts, the actual total airflow through the AFM's cross section can be numerically different.

It's that simple.

Further complications though are that the bodies of these AFMs are not meant to take boost inside them. Not really strong enough. Also, they are meant to pull air that is ambient. After turbo and before intercooler, the air can easily be >100°C. I do not know specifically what the max temperature that they will work at is, but you have to remember how these things work. They work by measuring the temperature of the air (that's the small upstream bulb on a wire sensor) and then the measure the current required to keep the hot wire at a given other temperature. That current is proportional to the mass flow rate of air over the wire. If you make the air really hot then you might approach the limits of where that sensing arrangement can work. (Or, you might not, as I said, I don't know the specifics of these units). It is definitely possible though that it is not very smart to relocate them to that location for that reason.

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