Thanks for all the replys. Yes the crank pully does remove the harmonic balancer, but think about this for a second. The flywheel is also used to reduce vibration in the crank shaft and their are some many people out there that are using light weight flywheels, with no problem. Also the pullies have been on the car for over a year now and belive me I drive it like it was made to be driven. The power gain from the pullies alone are worth the check engine light. One more food for thought, have you ever heard of knife edging your crankshaft, another racing trick, also messing with the balance of everything. The thing is I contacted Unorthodox Racing about the light and they said they had never heard of this problem before. So I'm woundering why mine is the first. The first time I was on this web site I read about a check engine light in 2000 GTS models that was for a misfire or random cylinder misfire code and it said that there was a ecu/fuel injector problem. The only way to get the code to go away was to replace the ecu with a 2001 GTS ecu and change out the injectors to the replacement ones. Has anyone had to do this yet? I have also had the car hooked up to an ODB2 scan tool and watched as it reported over 20 misfire at 2000 rpm within seconds, but the car doesn't miss a beat. The stupid light dosen't really have any effect on driveablity at all, it's just a pain in the ass to see every day. Other then the light the pullies have had no bad effects on the engine. They have proven to be one of the largest power gains for the money that I have installed so far.