AFM Question - High Comp Engine with Motronic 1.3

Post Mon Jan 19, 2015 10:31 am

Just wondering if someone could clarify something about the fitments and compatibility of AFMs across the range.

Are early high comp 325i AFMs and later low comp 325i AFMs the same?
Does it depend on whether it's Motronic 1.3 or not?

I think that my AFM has been "adjusted" in the past and messed around with so I'm looking to get a good used repalcement which hasn't been messed around with, but not sure what one to go for.

My engine is an Early High Comp M20B25, but with the later Motronic 1.3 fitted to it.

What AFM do I need?

Thanks!

Post Mon Jan 19, 2015 11:34 am

Same part number.

Post Mon Jan 19, 2015 11:58 am

bss325i wrote:Same part number.

Perfect, so any AFM off a 325i will be a perfect replacement right?

I'm guessing that 320i AFMs are different?

Post Mon Jan 19, 2015 12:53 pm

Yes 320 Afm is different

Post Mon Jan 19, 2015 1:06 pm

Assuming your turd does not have an o2 sensor, and there are no vacuum leaks and the tappets / throttle switch are all set up correctly, just get your mixture checked and adjusted to 1% ish.
Most if not all AFMs will have been tinkered with and replacing one that is working but not optimized for your engine is just going to get you another that is not correctly set.
Nothing wrong with tweaking the mixture screw , unless it is done to in an attempt to mask / fix another issue.

Post Mon Jan 19, 2015 1:46 pm

pacerpete wrote:Nothing wrong with tweaking the mixture screw , unless it is done to in an attempt to mask / fix another issue.

Don't let Brian hear you say that!

Post Mon Jan 19, 2015 2:54 pm

Mitchen wrote:
pacerpete wrote:Nothing wrong with tweaking the mixture screw , unless it is done to in an attempt to mask / fix another issue.
Don't let Brian hear you say that!

Too late!
That's the problem; it is "done to in an attempt to mask / fix another issue". Why else would anyone adjust it?

Post Mon Jan 19, 2015 3:31 pm

Is there a way of resetting the AFM back to factory settings?

Post Mon Jan 19, 2015 3:46 pm

German-Whips wrote:Is there a way of resetting the AFM back to factory settings?

Get the car 100 % and then get it hooked up to a CO meter and adjust to spec, I;E 1% ish at idle. ASSUMING no o2 sensor is fitted.

The joyz of cobbled up turdz !

Post Mon Jan 19, 2015 4:35 pm

pacerpete wrote:
German-Whips wrote:Is there a way of resetting the AFM back to factory settings?

Get the car 100 % and then get it hooked up to a CO meter and adjust to spec, I;E 1% ish at idle. ASSUMING no o2 sensor is fitted.

The joyz of cobbled up turdz !

Apparently can be done by applying voltage to two of the pins and checking for resistance at certain points in the sweep of the needle.

The "mixture adjustment" is simply a gross adjustment of the resistance of the AFM if I remember right.

There is a web site about doing this on the 944 as they used the same/similar AFM.

Post Mon Jan 19, 2015 4:45 pm

Any quick way of checking if my car has an o2 sensor fitted or not?

Post Mon Jan 19, 2015 5:00 pm

German-Whips wrote:Any quick way of checking if my car has an o2 sensor fitted or not?

A car with a factory fitted M20 has the plug underneath the battery tray. If an o2 sensor is fitted, it will be connected to this plug and the loom will run down to where the sensor is screwed in to the downpipe.