Expert: Josh Fields - 8/14/2006

Question
Hi Josh

I have a 1987 BMW 325 with the basic Motronic fuel system and completely stock ignition.  My car has started to misfire under acceleration.  It doesn't do it all the time, but it does it more when its cold or when its working hard (climbing mountains).  It seems to miss just as the accelerator is depressed.  Idle is fine and cruise is fine.

If I make small throttle changes most of the time I can avoid the misfire.  If it misfires,  ususally just misfires once and then its fine.

I bought this car new in December 1986, and the plug wires may be original (I have 187K miles), and I am going to replace them.  I replaced rotor and cap approx 50K miles ago.  O2 sensor was replaced about 40K miles ago.

Would appreciate any advice or guidance you could give me.

thanks in advance

Doug Stewart

Answer
Doug,
 I'm 99.99999% sure that the plug wires are your problem.  They break down from the high voltage.  Your symptoms are EXACTLY what Ignition break-down symptoms are.  It happens to every car eventually, and I'm actually EXTREMELY suprised you've made it this far without replacing them (187k miles...WOW).  The wires are not cheap, but they should last a long time (if you buy the quality ones).  Give those things a change and I guarantee you will be running smooth again!

 Good luck,
 Josh