this is from techinfo
ON TO THE EVILS OF BOSCH!
Bosch acknowledges a problem with using their Bosch Platinum spark plugs
in engines with ignition systems that employ 1 coil for each pair of spark
plugs (also known as a "waste spark ignition system"). Our GM 3800 engines use such a system.
The problem that Bosch has acknowledged when using their Platinum plugs
in engines with waste spark ignition systems stems from the tendency of
electrode metal to get transferred depending upon the polarity (direction
of current flow) of the spark. In waste spark ignition systems, 1/2 of the
plugs always see reverse polarity sparks. Given the very narrow platinum
center electrode of the Bosch Platinums, performance will be degraded more
significantly when reverse polarity sparks will cause material to be
transferred from the large ground/outer electrode onto the narrow platinum
center electrode'* exposed end surface.
Many of our members have had the same problem when Bosch plugs were chosen without prior knowledge of these issues. Our experience backs up the findings above.
If you want to research this further for yourself, try a simple google or Yahoo search on the terms BOSCH WASTE SPARK.