Relocated Afm Now Idles High

[sirdriftsalot]

Hey guys,

I've recently re located my afm to my intercooler piping on my34 the car drives fine except for when idling.

Sometimes it would go up and down and if it doesn't it would idle over 1000rpm

Any help would be great cheers guys

[GTSBoy]

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?

[sirdriftsalot]

Ah doesn't matter I've changed it back.

Sound was good, but CBF with the problems

[_x_FiReStOrM_x_]

Check and double check again for vacuum leaks mate.

[kitto]

When you move the AFM. Requires a retune.

[sirdriftsalot]

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

[kitto]

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]

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]

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.

[1400r]

^ 35 gtr afm hotside in whatever pipe size to suit power level job done

[GTSBoy]

Ferchrissake. He's not even got programmable management and you want him to change to your favourite new toy?

[Piggaz]

What was the reason for moving it?

[sirdriftsalot]

Got new cooler piping and told it was "better" the flutter sounded nice but idled like poo.

It's back to standard now, all cool on the pool.

[R31Nismoid]

Ferchrissake. He's not even got programmable management and you want him to change to your favourite new toy?

Blind leading the blind

[Dose Pipe Sutututu]

Got new cooler piping and told it was "better" the flutter sounded nice but idled like poo.

It's back to standard now, all cool on the pool.

just curious, who told you this?