Does your Ski-Doo 600 SDI foul spark plugs during warm-up? Or, does it surge excessively when the pipe is cold during acceleration? Ski-Doo has made available a revised ECM program for those 2004 600 SDI models and 2005 MX Z 600 SDI Renegade models that exhibit these symptoms (other 2005 600 SDIs are not affected). The new calibration is said to reduce the possibility of plug fouling, provide more consistent performance at higher elevations, better maintain a consistent pipe temperature to reduce â€œcold pipeâ€ surging, and to reduce backfiring when you cut the throttle. Weâ€™re told that only those machines which exhibit these symptoms should have the update installed.