AFM Adjustment...

[Rustam]

For those who are interested in AFM adjustment procedure I added another webpage to my site. It talks about the theory, significance of the flap spring and bypass screw, and the adjustment procedure itself...

http://mysite.verizon.net/vzerdcib/e34a/id6.html

[SchnellE34]

Very nice website, keep up the good work.

[Rustam]

Very nice website, keep up the good work.

Thank you, I am glad you've enjoyed it...

[bahnstormer]

thanks! this is very cool, only problem i see
(gave it a quick skim maybe its addressed)
is that u are setting idle afr...what happens
at 6000rpm?

[Rustam]

thanks! this is very cool, only problem i see
(gave it a quick skim maybe its addressed)
is that u are setting idle afr...what happens
at 6000rpm?

what is "afr"? air flow ratio?
you should read the theory - the ratio is not set for the idle only but is set for the whole operational band. It just happens to be set at the idle...

[nariusb]

This is a great help. Thanks Rustam.
One question, please. Is what you call the "Link" a switch and does it disconnect the wire #2 to O2 sensor? Do all the readings/udjustments to be taken with this wire #2 disconnected from O2 sensor?
Thanks

[genphreak]

thanks! this is very cool, only problem i see
(gave it a quick skim maybe its addressed) is that u are setting idle afr...what happens at 6000rpm?

Yea I like that write-up. It will be hard for some to follow but the good thing is its suitably technical for others...

I have been loking for a definate procedure to 'baseline' my AFM but had resolved to wait until I get a modern MAP sensor and ECU to replace the whole thing. Mine is good, but I suspect that many as they age suffer from spring deterioration which will affect the whole curve as well as shift the baseline air flow measurement. The point being; is the curve affected uniformly or is different depending on the Air Flap position... I mean by the time the AFM adjustment is out of whack the whole spring might be so out that the rest of the flap range may be way out of whack, thus it may be worth replacing the spring.

Does anyone have a way to buy some of those springs and the PCB for Bosch for BMW AFMs? The AFM rebuilders have to get them from someone... given that this definately affects our gas mileage a lot, we really need to find a good fix for this friends...

Absolutely great write-up Rustam!

[Rustam]

This is a great help. Thanks Rustam.
One question, please. Is what you call the "Link" a switch and does it disconnect the wire #2 to O2 sensor? Do all the readings/udjustments to be taken with this wire #2 disconnected from O2 sensor?
Thanks

"Link" is a switch.
Wire #2 must be disconnected during the procedure.

The switch is really superficial, it just lets you connect the system to observe operation of oxygen sensor as described in Bentley manual.

However, there are multimeters that enalbe the person to record "average value". When one uses such multimeter the "Link" switch allows the person to see whether the average value of the fluctiating voltage in open loop ("Link" disengaged) and closed loop ("Link" engaged) are same. They must be same - this way the map margins are adjusted with margins of operation of oxygen sensor.

Without such multimeter one should simply note on the position of the screw at the point of getting the mixture lean and at the point of getting the mixture rich after the adjustment. The middle position of the screw between those points is assumed optimal.

As soon as I am able to invest in one of such multimeters I am planning to provide an update on "fine tuning". Alas the results are satisfactory already. If you feel that the engine still consumes too much gas or too hot try to turn the screw within the limits of optimal operation (while the voltage fluctuates the screw is still given some freedom).

[Rustam]

Yea I like that write-up. It will be hard for some to follow but the good thing is its suitably technical for others...

I have been loking for a definate procedure to 'baseline' my AFM but had resolved to wait until I get a modern MAP sensor and ECU to replace the whole thing. Mine is good, but I suspect that many as they age suffer from spring deterioration which will affect the whole curve as well as shift the baseline air flow measurement. The point being; is the curve affected uniformly or is different depending on the Air Flap position... I mean by the time the AFM adjustment is out of whack the whole spring might be so out that the rest of the flap range may be way out of whack, thus it may be worth replacing the spring.

Does anyone have a way to buy some of those springs and the PCB for Bosch for BMW AFMs? The AFM rebuilders have to get them from someone... given that this definately affects our gas mileage a lot, we really need to find a good fix for this friends...

Absolutely great write-up Rustam!

Thank you Gen I am glad that you have enjoyed my website. I recall you also were able to use some info on shifter switch.

regarding the question about affecting the curve by the spring - from practical standpoint I don't think that the spring deteriorates to the point of being unable to provide matching response to the curve.

It is fairly long - the longer is the spring the more uniform is the force it provides to countract compression within given limit. If the spring was short then we would expect it to provide progressively increasing resistance. But resistance in this case increases at uniform rate since the spring is long.

Bottom line - it can become less resilient, but the laxing effect would still be uniform through turning space making us able to simply tighten the spring and experience conforming operation again...

[genphreak]

This is a great help. Thanks Rustam.
One question, please. Is what you call the "Link" a switch and does it disconnect the wire #2 to O2 sensor? Do all the readings/udjustments to be taken with this wire #2 disconnected from O2 sensor?
Thanks

Yep, you need this to be able to control the ECU behaviour whilst testing... the Bently explains it, perhaps Rustam will embellish more around it at some point.