Need An E36 Master: 1995 E36 318is Air Flow Meter (afm) Function

[Boosted318is]

I have supercharged 1995 BMW 318is, M42 engine DME M1.7.2. I need to find out how the AFM processes the signal to the ECU.

I attached an electrical diagram.

My AFM is a 5 pin meter with the following pinout:

PIN 1 – 5V input reference signal from pin 59 of the DME

PIN 2 – Part throttle signal output (0-5V) to the DME pin 41

PIN 3 – WOT Signal output to DME pin 76

PIN 4 – IAT input to DMW Pin 77

PIN 5 – Signal GND, PIN 14 on DME

I am converting the car to a Mass Air Flow (MAF) System. Here is the dilemma, the AFM has a 5 pin harness with the following pinout. A MAF has a 4 pin harness with a single 0-5v signal regardless of throttle position.

I currently have the MAF conversion hooked up, but I cannot get WOT to engage. So how do I get the independant WOT signal into the ECU?? Can I just run the same 0-5V line from the MAF to both PIN 41 and 76 of the ECU??


I need to know how the AFM communicates partial load and WOT on Pins 2 and 3 given its 5V signal input. Any help would be awesome.

[Hammdy]

Well I'm not quite sure that I understand you perfectly here, but the normal setup is that there's a 'switch' that detects partial throttle, and above 66% throttle (or so, can't remember exactly) it hits another switch telling the ECU 'full throttle'. On the setup you want there's no one point in which it changes the fuel injection map to 'full throttle', it just uses a potentiometer to read the exact position of the throttle butterfly. In otherwords, it shouldn't "get WOT to engage". What should be happening is that as you open the throttle more, your multimeter should linearly show an increase in voltage. Hope that helps a little.

[Boosted318is]

Based on the above diagram,
The problem is that Pin 3 of the AFM does not output a signal that varies with the door position. Pin 2 produces that signal. Actually I cannot get an output from pin 3 at all. I am trying to figure out what pin 3 is used for.

[Hammdy]

Hmm...well what I was saying early mostly applied to the throttle position sensor, so ignore that.

Pin 3 should produce a voltage once the door/flap thing inside the AFM opens almost all the way.

[bmwman91]

Pin three is the LLCO (Low-Level Carbon Monoxide) sensor. It is only used on non-catalyst equipped cars. The E30 and E36 M42's use the same AFM's, and it happens that E30 wiring diagrams are a bit more informative abotu what is what (they don't however show any of the input signal circuitry for the Motronic...I had to find the voltage divider resistors myself with a multimeter!).

Anyway the AFM has nothing to do with the throttle position input to the ECU. That is determined, as you may guess, by the throttle potentiometer on our throttle bodies. The AFM gives out a continuous logarithmic (or exponential, I cannot remember offhand) voltage vs. airflow transfer function. Reconnecting pin 3 would not do anything good for you (if th US Motronic's even have the pin connected at all).

The AFM is just a potentiometer with a sprung actuator that is moved by passing air. The 5V reference put out by the MCU passes through a 1KOhm resistor as the first half of a voltage divider, and the variable temp/flow resisrtors are the divider's other half. The ECU's MCU reads the divider-midpoint sensor output voltage through its ADC (channel 6 I think it was for air flow). As my senior engineering project in college I made a MAF conversion, and I can tell you anything you need to know about how the ECU takes/uses the AFM signal, and how the sensor works.

Heck I would assume you are asking about the input system because you want to use a MAF. To answer the likely following question: No, you cannot just wire in a MAF and go. The ECU will not 'learn' to use it, and will just be extremely confused, causing either detonation, or ignoring it and running the 'limp-home' maps. Some MAF's don't even put out analog signals like the AFM/most MAF's, making it completely useless without signal conditioning. If you are interested in a MAF conversion PM me. Anyway, any questions you have I will gladly answer here!

[ironH]

Do anyone have some details for changing the intake from a m44 on a m42?
i wanna do it with da ECU update...

For the future i want to install this


Kind regards

[guygti22]

i would love to be able to trash the afm and just replace it with a honda civic maf. any way to do this ?cheaper than buying a new afm for 300? lol

[Robi čepin]

Pin three is the LLCO (Low-Level Carbon Monoxide) sensor. It is only used on non-catalyst equipped cars. The E30 and E36 M42's use the same AFM's, and it happens that E30 wiring diagrams are a bit more informative abotu what is what (they don't however show any of the input signal circuitry for the Motronic...I had to find the voltage divider resistors myself with a multimeter!).

Anyway the AFM has nothing to do with the throttle position input to the ECU. That is determined, as you may guess, by the throttle potentiometer on our throttle bodies. The AFM gives out a continuous logarithmic (or exponential, I cannot remember offhand) voltage vs. airflow transfer function. Reconnecting pin 3 would not do anything good for you (if th US Motronic's even have the pin connected at all).

The AFM is just a potentiometer with a sprung actuator that is moved by passing air. The 5V reference put out by the MCU passes through a 1KOhm resistor as the first half of a voltage divider, and the variable temp/flow resisrtors are the divider's other half. The ECU's MCU reads the divider-midpoint sensor output voltage through its ADC (channel 6 I think it was for air flow). As my senior engineering project in college I made a MAF conversion, and I can tell you anything you need to know about how the ECU takes/uses the AFM signal, and how the sensor works.

Heck I would assume you are asking about the input system because you want to use a MAF. To answer the likely following question: No, you cannot just wire in a MAF and go. The ECU will not 'learn' to use it, and will just be extremely confused, causing either detonation, or ignoring it and running the 'limp-home' maps. Some MAF's don't even put out analog signals like the AFM/most MAF's, making it completely useless without signal conditioning. If you are interested in a MAF conversion PM me. Anyway, any questions you have I will gladly answer here!

Hi..i know this is an old thread ....i cant send you pm..i am wery interesting in maf conversion on my e36 316i..can you helo me?