Thread: DIY: SAP Sim
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Old 02-22-2013, 06:27 PM   #49
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Join Date: Jan 2011
Location: Littleton, MA
Posts: 6
My Ride: 2003,325i
M56 Sim....


I measured the Secondary Air - Mass Air Meter output using a shop vac to simulate the moving air. This a crude test. The secondary Mass Air meter w/o air flow had 60mV output. When the shop vac was pushing air through I got 3V output.
So, for now I made a voltage divider at the plug to keep the voltage at 2.5V.
The power pin supplied 5V so I used two 10k resistors tied together. One end going to the ground pin one end to 5V pin and the signal pin went to the junction of the voltage divider. Right now I still get the P1418 code with the sim alone. P1418 is Secondary Air Hose Clamped. I am assuming the air mass meter thinks there is no air flow so it thinks the air hose is blocked ( manifold valve closed).

The O2 sensors are the 5 wire type.
Combined Narrow Band and Pump Cells (5-wire).
Red wire = Ip
Yel wire = Vs/Ip
Blk wire = Vs
Wht wire = Heater-
Gry wire = Heater+
(All on the O2 sensor side of the plug.)

The formula for the O2 sensor is:
Vs = (RT/4F)*In(pO2atm/pO2test)
so the voltage range for the sensor is 0.9V for low oxygen and 0.1V for high oxygen. Wow, this is non-linear. The most linear part of the range is between 0.7V and 0.2V
Stoich is close to 0.45V (mid-range) so 0.2V is on the Oxygen rich side.

Sorry for the rambling but, just trying to get a grip on this as I write....
jbielefeld is offline   Reply With Quote