Posted by Don Daynes on March 07, 2001 at 02:24:59:
For those keeping track. My 81 528i failure to pass NOX was due to a bad ECU. Besides not passing the NOX component of the test, the car ran fine. The AFM could be adjusted for proper DVM readings at the O2 sensor and my CO meter had good readings. Using the Split Second Air Fuel ratio meter told the story. The dog weren't hunt'n. The LEDs would hold steady, abruptly reading lean at some speed, that varied with how the AFM was adjusted. I had swapped out the ECU on a number of occasions but the DVM and CO meter read the same. Remember throughout the car ran fine. Swapped the ECU out once more with the A/F ratio meter wired in and.... bingo. This dog hunts. LEDs cycle back and forth never really stopping in the center. The fact that it was not hunting was easy to overlook with the DVM as the voltage was fluctuating somewhat.
BTW the spare ECU is the 0-280-001-118 unit (79 5281). There was some discusion back in Sept. about the differences between it and the 0-280-001-122 (80 - 81 528i) unit. The -118 works fine in my 81. For comparison I also pulled a -122 out of my 81 3.5L car and and tried it. The car drove the same and the A/F ratio meter gave the same readings with either one in the car.