transmission: fuel evaporation

hey its my first post here and i have a few questions. Well ill start off by saying back in june my transmission was shifting hard intermittently through eery gear, had the valve body replaced about $900. then about 2 weeks ago my car stopped getting power to the wheels. the torque convertor was totally destroyed as well as the rest of the transmission another $2500. the only good part in it was the valve body. 2 days after i picked my car up the "service engine soon" light came on so i took it back in, they said it was the gas cap and reset the light. The following day it came back on again i took it back and they said i need a new gas cap. I bought one and the light has yet to go off, 3 days later. I dont know the code number but the code stated "fuel evaporation" and the tech mentioned something about a vent in the gas cap. Does anyone know if it is necessary to take down fuel lines and vacuum lines in order to drop the transmission? It seems very weird to me that before it went in the gas cap was fine and now after they worked on it they say i need a new one. Please help, im going back tomorrow to get them to reset the light to see if it was the gas cap.

Well, it's possible that it is your gas cap; it is supposed to be turned at least three clicks when replacing. This is the cheapest possible solution to your problem. It could also be that they knocked something loose in the evaporative emission control system, of which the gas cap is considered a part. There is a canister behind the driver's side rear wheel that traps evaporated fuel and recirculates it to the engine via tubing and a solenoid that is in the engine compartment. Yours is a '98; my '98's solenoid had to be replaced after it was manhandled during an upper intake manifold replacement. I suggest requesting another gas cap first - GM replacement parts are notorious for being defective, since they frequently are defective assembly line parts repackaged for sale as replacement parts. And check the solenoid and associated lines for integrity. If there is a crack/break of any sort you will also get a code light set. As I recall, the solenoid is sold as an assembly along with a portion of the tubing - but not all the way back to the canister. Good luck and sorry to hear about your transmission troubles. Welcome to Oldmobile ownership!! :banghead: