Re: misfireing and rough acceleration (archive)

I doubt the rotors are causing the burning smell, but here is the problem with a worn cap and rotor. The distance the spark has to travel from the rotor to the cap is longer. Therefore it takes more time. The more time it takes, the more it retards the ignition. The computer will compensate for this up to a certian point, but after that, you keep getting later and later timing, which deacreases power and could cause the burning smell because you have passed TDC of the firing stroke, so now you are loosing compression while trying to burn the mixture. When doing this, it does strange things to the burn paterns and what you may be smelling is incomplete combustion, or improper combustion. I had this same problem when it rained the second day I had my car. The cap was cracked and let a little moisture in and then it was all over. The car had the same symptoms as you are describing, but it was so bad that I couldn't even drive the car to my mechanic.(Didn't have the knowledge then that I have now). Anyway, try it, it is always good to replace them every 60k as they go bad right around there. You should see a marked improvement in the performance and drivability. If the cap and rotor you take out is REALLY worn, I suggest unpluggin the motronic unit for 10 seconds to reset it, so that it doesn't have a shock when you have the new cap and rotor in and it fires off the mixture really early.
Hope this helps

Rob A
M535i SIG Technical Advisor
www.M535i.web.com

http://www.geocities.com/bmwhartge

Follow Ups:

[ Follow Ups ] [ 5-series (E28) Message Board ] [ Msg. Board FAQ ]

Questions, comments, or problems, please visit the Roadfly help desk.