The check engine light came on in our pretty burgundy red 1989 244, and from tailpipe odors, I could tell she was running rich. Gas mileage had dropped to about 14 mpg.

Armed with lots of BrickBoard knowledge and a little personal experience, I began trouble shooting. I read the OBD codes: 231 and 113, I believe (fuel trim/lambda control, too lean or rich at part load – duh, my nose narrowed it down farther than that!). Because of the lambda reference, I first checked the O2 sensor. I looked for wiring faults and even checked the sensor voltage as described in the BB archives. It seemed to be functioning properly. Still, the OBD codes seemed pretty certain, so I pulled the sensor from the cat, cleaned the tip using fine steel wool, and reinserted it. I then reset the fault codes and started the car. The light stayed off at idle, but as soon as I began driving and accelerated it came back on.

I considered just purchasing an O2 sensor, but instead, I put in a used one from my spare parts cache. No change; and I was finally ready to give up on the O2 sensor. I then checked for vacuum leaks, made sure all cylinders were firing by sequentially removing spark plug wires, replaced the plugs and distributor rotor/cap, checked the flame trap and associated plumbing. I even checked that little brass fitting that screws into the intake manifold. A year ago we got a check engine light on a 91 244 (different OBD codes, though) and I found that fitting almost completely clogged. I cleaned it and the problem went away.

Back to the problem with the ’89! I next cleaned the throttle body, including the little holes near the butterfly valve. It was rather dirty, but the problem did not go away. I changed the air mass meter, still no solution. Well, now I WAS getting concerned. I did not want to go to the dealer. As somebody who is supposed to do engine design research, I would have never lived it down if I had been defeated by an idiot light. My thoughts turned to the fuel system. I changed the fuel pressure regulator; again, no change. I considered the injectors. However, because the check engine light seemed to come on at both very low acceleration rates as well as normal rates, I decided the injectors were probably ok. My (probably spurious) reasoning: the CE light had just began coming on, so if bad, the injector(s) must have only just gone out of spec. They should still be able to properly meter the fuel at part load.

Finally, decided to change the ECU. The one in the car was a pink label 561. I replaced it with a 951 from the parts box. That finally fixed the problem! It has remained fixed for a month now.

The moral to the story is to be wary of those pink labels ECUs. Even if the car continues to run.

Happy bricking! Glen