anybody near their car with a multimeter?

[hoshy]

could do with a few examples of the voltage across pins 1 and 3 of the air meter. It's the CO adjust voltage, it will be between 0 and 5v+

Pins are numbered clockwise starting top left as pin 1 (about 11 o'clock)

car needs to be running.. the colours I have on mine are blue/grey for Ground and black grey for CO voltage.

Thanks for even reading

hoshy

[Martinaston]

318is ?

[hoshy]

any e30 will do. I'd like to get a cross section of results.

I'm expecting different results from all cars but also that they're in the vicinity of 3 - 4 volts. Unfortunately my car is 200 miles away and the AFM I have on the bench, I turned the CO adjust to many times whilst trying to determine the pinouts.

[Martinaston]

The 318is/318i/316i has the round connector on the AFM and all the other's i've seen have a flat five pin connector but only use four pins.
I'm preety sure the CO screw is not linked to them as all it is is a bleed valve to restrict the air flow, i think the wires your after are for the air temperature sensor. The little wire poking down from the top if you look into the inlet side of the meter.
So the reading you get should vary with the ambient temperature for that day.
According to bentleys at 20c it should have a resistance of between 2200 and 2700 ohms.

Is this for a MAF conversion ?
If so that part should be a straight swap like for like as long as the new MAFM is a five volt unit.
I'm not too sure how the MAF works on the air flow side (vibration i think ?) but with the old AFM it's just an increasing resistance as the flap opens.

Hope that's of some help.

[hoshy]

The CO screw on my m40b18 is connected to a multiturn pot, it varies the output on pin 3. voltage ranges from 0v to supply voltage (5v)

As far as I can tell it doesn't affect the flap output (0.255v - 4.9805v) at any point in the flap's arc.

The temp sensor give ~2k at room temp and is connected between gnd and pin 2.

The temp sensor on my 5v MAFs also reads ~2k at room temp. and drops by the same amount when you warm it to body temp (very scientific this ) So, I reckon I can directly connect this. which is a bonus.

The reason I was interested in the CO adjust outputs of other people was because during testing I fiddled a bit too much with mine and I don't know where "normal" is. I guess it will change a little for each setup but be somewhat similar. I'll need to simulate the CO adjust voltage in my signal converter so I also wanted some example values.

I've not seen many AFMs but the m40, m42 and early e36 318iS (m42/m44 ??) all have round connectors. As did my early m20b25. Which cars have you seen with a different connector? I'm gonna have to get one of those to play with

[Martinaston]

I've got the 320 and 325 motronic one's here and they only have four terminals on them, the CO screw normaly sits about three turns up from the bottom. But as to exactly where, you'd need to stick a gas analyzer on it.

I think i've still got one from a 316 somewhere i'll dig it out later.

[hoshy]

Interesting. I've not seen this type.

I guess later on they moved to an electronic CO adjust.

And change of a pic?

Here's mine.



You can see the CO adjust pot (blue rectangle) in the top right.

[Martinaston]

So does the CO screw actually restict the air flow, or is it purely electronic ?

[hoshy]

on this type it's purely electrical.

[hoshy]

Anybody got any measurements?

[hoshy]

anybody out tinkering ?

[stevetigger]

You know I would do it for you but.........

[Martinaston]

If it's just a pot can you not just measure the resistance at each end of the adjustment and go from there ?

[hoshy]

cheers Steve

Martin, the point was I wanted to get an idea what values we're common. Given that the output changes from 0 - 5v over 10 plus turns of the pot there's room for a wide variety of settings.

[hoshy]

fwiw, mine came in at 1.37v