Hi fellas,
I wrote a few weeks ago about my wife's '91 245 poor fuel economy and rough running. After replacing the AMM and the oxy sensor, the FPR, and the Coolant Temp Sensor, the car continued to run rich and rough and hard to start on hot days. I was at my wits end. All the tests checked out good with the OBD. What could be the problem? THEN, my wife said she heard a shart snapping sound while at the drive thru for fast food. I doubted her and said she was hearing things, the I heard it. I lifted the hood and saw a sporadic spark and snap off the coil's positive terminal. It was arcing and the engine would run rough when it did. Weird. Bad Coil??? Well, I went to the local parts store and bought a coil. Then, when I started taking the old coil off I noticed a rather large crack beside the positive terminal. I did not make the crack. The coil looked old. Anyway, after I replaced it with the new coil, the car runs wonderfully. No hesitation, no coughing, no difficult starts, great accelleration and response. How often does this happen? Why would it spark? And why would the sparking (short) cause the rough running? I am happy now and so is the little woman, but I want to understand the reason the bad coil would do all this.