FAC-2 Fuel Control Unit Carerra

onefstm · 02-20-2005, 06:29 PM

I found this unit wired into the computer of my 85 Euro 911. Does anyone have any experience with it? The car now has a cat on it so I wonder if this was developed to help with emissions or if it some early version of a performance chip.

Wil Ferch · 02-21-2005, 06:00 PM

Why not call the number and ask ?

Wil

onefstm · 02-22-2005, 07:18 AM

The number on the unit is no longer in service. I did a further examination of the wiring and determined that there is one wire going to power, one to ground, and two wires in the unit that are spliced into the wire which is black with a red stripe ( I think --- I need to double check my pictures). From what I can gather this unit was added to the stock European unit to add an oxygen sensor that was needed to work with the added cat. Last night, I disconnected the unit and found that the car now seems to idle lower and run rich at idle. I have a Euro premuffler on order and should have that installed by this weekend.

Does anyone have any thoughts on why the car now runs rich? Should I check the adjustment settings on the ECU? Also, I read that there are an idle adjustment setting on the AFM and also a CO adjustment. Should these be adjusted. I would like to get the car back to Euro specs so I would prefer to remove this unit.

RickM · RickM's Garage

Found it here: http://bimmer.roadfly.org/bmw/forums/e23/900880-3.html

Allegedly it's "Fluff for the Feds"

EDIT: spelling

onefstm · 02-22-2005, 10:08 AM

Rick,

Thanks for the research. The box did appear to do something as the car seems to idle richer. However, I plan on leaving the unit out and readjusting the idle mixture. Any advice on this procedure?

Rot 911 · 02-22-2005, 10:13 AM

One, if that unit is actually acting as an O2 sensor, you probably should leave it hooked up. On a U.S. version of the 3.2 the DME goes into a default "limp home" mode when the O2 sensor is disconnected and the fuel mixture becomes extremely rich. There is no HP gain by disconnecting the O2 sensor on a 3.2.

ausdilecce · ausdilecce's Garage

Also note that hving an o2 sensor on a car actually makes it run *better* since it can adjust the AFM based on real data ( from the O2 sensor) rather than adjusting the AFM based on air/fuel maps.

Air/fuel maps are great UNLESS you have climactic conditions that the air/fuel maps cannot compensate for ( high humidity, low humidity, smog )

AFAIK, the motronic unit takes these variables into account
altitude ( with a simple on/off switch ) - higher altitude = lower oxy content
temperature ( with a probe in the air meter box ) higher temp = lower oxy content
air *volume* ( with the air meter )

onefstm · 02-22-2005, 12:51 PM

Guys, dont get me wrong. I am a big fan of o2 sensors. However, this computer does not support an O2 sensor as this car is a Euro model and did not come with a sensor or a cat. This unit appears to be a band aid to make the car comply with EPA emissions. I also emailed Steve Wong who thinks that it may be best to remove this unit and return the car to Euro specs.

KobaltBlau · 02-22-2005, 02:06 PM

I wouldn't be surprised if it modifies some other input to the ECU based on the O2 sensor reading. I considered an 86 for purchase with this setup (definitely an 02 sensor control, installed in the federalization process.) but didn't research its function in detail.