AFMs: Should we all do this?

[genphreak]

Hey all,

My AFM was damaged previously by someone tightening the boot hose-clamp too much which crushed the round mating surface into a crooked oval, which then introuduced a leak I have never been able to fix.

Off I went off to get a new AFM, the first from eBay turned out to be the wrong one and was damaged in transit, and now I've got the second... which of course has turned out to have some bad bits.

So I ended up having to rebuild it with good bits from my old one. Luckily there's discussion's on adjusting them, so I was able to glean some assistance on the job - (in-situ calibration of the M30 L6 EFI)

Anyway, my task is complete now, but it dawned on me that if those that were doing this were advancing their old AFM springs 2-3 notches (which mine needed too), perhaps it is more than just co-incidence!

ie. Maybe the springs are loosening with age (how floppy would you beif you were bound up in a dark hole for 15+ years?). I guess if this is so, they aren't metering the air quite right anymore.

Perhaps others have some experience here? My car was definately running/idling a little weird, (More on the results of this soon once I've had a chance to test it) maybe with that spring potentially too loose, the air flap would have been a bit liberal on the engine's air requirements...

GP

[Jeff N.]

Maybe. Changing the spring notch point will lean/richen the car over the engine band. I tinkered with this several years ago and was never sure about the positive effects. In the end, I ended up tossing my old afm and went to a rebuild unit.

You can definately adjust the air bleed screw with good results.

Note that Louie doesn't have any drive report; he's just adjusting for idle.

Jeff

[Rory535i]

You can definately adjust the air bleed screw with good results.

Jeff

where does the air bleed screw live?

[Jeff N.]

it's clearly shown in louie's site. under the afm.

[Rory535i]

it's clearly shown in louie's site. under the afm.

oops... thanks

[genphreak]

Thanks for that Jeff...

My take on it (so far) is that the Bosch factory would set the spring tension (I imagine they'd do a flowtest and set the flap gap at the end of the production line, thus being an ideal moment to set the spring tension and sealing the unit). I guess BMW would request the AFMs be delivered so they just bolt them onto the cars in their factory and do the least amount of adjustments on the line itself to speed up vehicle production.

BMW would then only need to set the idle switch and throttle cable settings before doing a small tweak of the AFM's air bypass adjustment screw once the motor is ready to do its first start. It'd be interesting to know if the factory CO setting is any different to wht they would be wanting to acheive delivery when the vehcile may have to meet emissions criteria (I wonder how close you can get the CO levels with an engine that hasn't run it yet...) well I suppose it's pretty close as they install a bung over the screw with a very German 'never to be touched again' attitude... LOL. But then again, there probably is no smog test when the cars are new... anyway... I digress... forgive me!

The point is that Bosch would need to be assuring BMW (most accurately) that any particular AFM would flow a certain amount of air at idle within a given tolerance.

To achieve this Bosch would adjust the spring tension by machine- probably using a tool that fits over the adjustment cog (looking at the way the AFM comes apart) and tightens the spring up to a certain resistance. They'd probably perform spring load tests at various openings but I can't see them bothering to actually set the tension settings at a higher flap opening than idle since that is what they would be producing the AFMs to achieve, first and foremost before they are packed for despatch.

I haven't set my air-bleed (CO) screw yet, but that is something that is directly related to the engine's settings (valve lash/engine condition) so have been leaving that to last. However for those that don't know, be sure to note that the air-bleed only adjusts the amount of air bypassing the flap at idle and has no affect once the engine is under load. It simply allows BMW to make up for small variances in the engines which affect the Carbon-Monoxide emissions.

Am just sealing the AFM today and putting it back on. I will provide a drivability report fellows... of course (hmmm now, what is tha maximum speed I ahve taken her to so far... ) . Thanks for noting the omission of the drive report in the link I referred to Jeff, results speak louder than postulations such as what I've contributed above, Will have a search arounf later to see if there are any drive reports on the boards since that documentation was done.

More soon...

[genphreak]

Hey everyone,

Preliminary drive tonight yeilded excellent results, my rebuilt AFM makes the low-end drivability much nicer, better off the mark, and the fuel consumption id definately better. More as I refine the results over the next few days.

GP

[grave77]

I have explored my old AFM for 2 years and tried all possabilities the best was when i tightend the spring 6 notches or more and adjusted the conductor pot. to the best idle by freeing it from the screw that hold its position. this made my car take off better than before but I lost a little at maximum speed. after 2 years it had a groove just like what happend to yours and that was one of the main causes of the black carbon build in my exhaust and engine. simply the resistance ratio wasn't correct anymore. ireplaced it with a second hand one that I checked before I paid for and it was good. if u had hard time with this ... we have ones here working second hand AFM for around 55 USD tell me if that suits u and helps u solving this pain. good luck

[genphreak]

I have explored my old AFM for 2 years and... ...we have ones here working second hand AFM for around 55 USD tell me if that suits u and helps u solving this pain. good luck

Hey thanks for your wisdoms grave77, I am not quite sure what to do yet. My pot's tracks (on the AFM PCB) are scored up a bit, but I've replaced my old bent up body... but am still fiddling. It looks like the AFM I got was off an earlier 533/733 so it had a few significant differences, am trying to use the body only, so swapped all my car's electronics and the spring which is fine so far- only diff in the housings is the way they are sealed up and the entry hole for the connector- I have to dremmel the older casting to make it fit. The connector piece is different though, ever so slightly- the 89 one had little wires soldered to the PCB as well as the copper contact fingers... (?) perhaps they weren't enough... i just don't get that black connector my 89 one has 5 tabs connected inside the afm and only 4 pins on the outside... the early AFM was straight through... weird German electronics knows no bounds to wizadry it seems... GP

If you have real nice one off a late 535/735 I'd be interested.. I don't like this unceratinty at all. The next step is a reco AFM or a MAF conversion kit... but that's too much... I don't have that much cash, or this much time... (cries)

GP

[grave77]

well ... I know how bad is the uncertinity. the modification wasn't that complicated .. I think they soldered the moving pot with a black wire to make sure it has better connection than the spring connector at the middle of the moving pot. axis. anyhow ... as I said the second hand good condition ( tested ) AFM is for 300 AED / 3.6 = 83.3 USD + shippment ... thats ur price ... e-mail me if u wanna go through and I will be glad to help.