AFM wot dos it do. Exactley

[LeonNewton]

So as in title. Wot does the afm do and haw does it do it?
I gess it meshers flow rate with the butterfly valve. But wot elce does it do and wot other info dus the ecu get from it?
If it is just a flow meater then wot advers afects on the engion would it have if I removed it from the airflow and Jamed it open. Or opens it up and poped a resistor in mimicing the signal of a fully open valve.

[spp320i]

I'm no expert, and I'm sure you'll get a much better answer from someone else, but just one thing I'd say - don't feck with it! If you jammed it open, I'd think your engine would run very rough, as the ECU needs to know how much air is being taken in so that it can deliver the correct amount of fuel. If you jammed it open, it would force loads of fuel into the engine and would run super rich - so much so the engine probably wouldn't run at all!

Someone else will correct me if i'm wrong, and supply a bit more knowledge than I can!

[LeonNewton]

Ok so... Wot about meatering the air passing the car and avalable for induction. Rather than the air actualy being indused. Wuld you get the engion running right then/ culd you get it running right then. Or ......

[spp320i]

fraid that's beyond my capabilities mate! I just think the AFM shouldn't be removed because it provides the ECU with info it needs to determine fuelling, and other such things. Hopefully you'll get someone with more knowledge to give you an answer...!

[clipper]

The air passing over a car (due to it´s speed) has nothing to do with the amount of air being sucked into the motor by the down stroke of the pistons.
The ECU needs to know specifically how much air the engine is taking in, there are better and more refined ways of doing this than the AFM, for example a Mass Air Flow meter which takes into account the density of the air for example and which I understand can be fitted to an E30, but I can't help you with that and really its too complicated to consider on an otherwise stock engine, and probably impossible with a stock ECU.

Someone who knows more about this upgrade can probably give more info.

[LeonNewton]

Chears bud.
I know or rather suspected it is important and not do withoutable. My drama is converting to itb's ther is no ware for an afm to go. Unless I have 4. Culd go to custom stand alone engion manadgement. Wuld like to get it running withough though.

[spp320i]

there are a few on the zone who run with itb's as far as i know, so there must be a solution.

Look hard enough and I'm sure you'll find it!

[DHFiS]

The 316 had a single carb and no AFM.

[mrLEE30]

with ITB you would need a custom ECU system, normally a stand alone system, with ITB's you still need to measure the air, and even ITB are be fed from a common plennum box, the air going into this box will pass through an air meter as is the case with the S14 (and even all models to this day)

, the E30 AFM is a rather crude device compared to modern MAF's although it does measure inlet air temp and thus from this the air density can be calculated, but rather the E30 ECU will have a mapping system. You car cannot run without it on a standard ECU, it may be possible to start and idle but not much more,

the only exception is if you run carburettors, but in this case the air is drawn into to carb due to the negative pressure of the cylinders and thus the fuel is drawn in with it, the jet size and needle dictate the amount of fuel to mix with the air.

[Banjo1981]

Yeah but a carb engine doesn't run fuel injection does it? I was always led to believe that the engine management is mechanical (needles, floats, jets and what not) as opposed to the electronic system on fuel injection models.

The way I understand it is:

When you put your foot down the ECU and AFM receives a signal from the TPS to tell it you're accelerating. The AFM opens to increase the airflow to the engine and the ECU increases the fuel through the injectors. Whislt this is happening the AFM feeds back to the ecu to tell it howmuch air is flowing to the engine so that it can contantly adjust the fuel for optimum efficiency (ie not too rich not too lean). At idle the AFM restricts the air flow as the ICV then takes over on some sort of vacuum system (which I don't fully understand).

The AFM is vital in allowing the ECU to control the air/fuel mixture into the engine preventing a whole host of running problems.

I think.

Anyone please correct me if I'm wrong as I'm always happy to learn.

Ant

[Speedtouch]

You can fit as an alternative, a Miller MAF http://www.millerperformancecars.com/ca ... egory_id=6

Or fit Megasquirt, which allows you to run without either AFM or MAF.

The AFM is essentially a potentiometer (variable resistor/rheostat) that is connected as a potential divider to give a varying voltage to the ECU depending on how open the airflow flap is.

[spp320i]

The way I understand it is:

When you put your foot down the ECU and AFM receives a signal from the TPS to tell it you're accelerating. The AFM opens to increase the airflow to the engine and the ECU increases the fuel through the injectors. Whislt this is happening the AFM feeds back to the ecu to tell it howmuch air is flowing to the engine so that it can contantly adjust the fuel for optimum efficiency (ie not too rich not too lean). At idle the AFM restricts the air flow as the ICV then takes over on some sort of vacuum system (which I don't fully understand).

The AFM is vital in allowing the ECU to control the air/fuel mixture into the engine preventing a whole host of running problems.

I think.

Anyone please correct me if I'm wrong as I'm always happy to learn.

Ant

That's how I understand it as well, hence why I can't see how the AFM can be removed.

But at least some knowledgeable people (MrLee) are coming along now!

[gareth]

you're on the right track - partly.

the AFM does not and can not control the airflow. it's an Air Flow Meter, it dies exactly what it says in the tin! it meters the air that's being drawn into the engine and provides a signal to the ECU, from this (as well as some other signals but lets not go into that now...) the ECU then calculates the correct injector duration to give the correct amount of fuel for the correct air/fuel mixture.

the flow if air is controlled by the throttle body (butterfly). this is controlled by your foot, via the throttle cable
at idle the throttle body is closed so the the air flow is provided by the idle control valve. this is a little valve that's controlled by the ECU that feeds the right amount of air to maintain a 800RPM idle state.

i think that should clear things up....

if you're fitting ITB's, you'll need aftermarket management that can sense the airflow in another manner.

if you're fitting carbs, you don't need to do this as they do everything the injection system does but in a mechanical and more crude manner.

[DHFiS]

With fuel injection you must have a means of measuring air flow into the engine.