I recently bought a 1998 750iL. The MIL was on, I checked OBD2 and it gave the codes for "cylinder misfires" on cylinder #7 & #9 . I replaced the spark plugs, and if you have ever replaced the plugs on a M73 you KNOW my pain. :-) The code for misfire on #9 cleared and the engine ran better, BUT #7 still shows a misfire. I removed plug wire and tested operation, Plenty of spark from both wire and new spark plug. Ran compression test on cylinder, tested around 30 psi. Hard for me to believe this is correct due to how well car runs. I'm going to try a different compression tester to double check my results. Another problem is I can't register the car in NC if it can't get the MIL light off! :-(
My questions are: Is this a common issue on the M73? If so what is usually involved in the repair? I've read that cleaning the intake or piston rings with Seafoam or K1 can help this problem, is this true? Is there a way to get the MIL light to stay off long enough to pass a state inspection?
This is my first BMW, I love the car and want to fix it properly, my background is in Japanese Industrial Equipment and American muscle cars. As I said... Please Help.