You can get various smoke effects 'out there' which you can then edit using Notepad. If you follow the Effects SDK it'll tell you all you need to know.

The figures are the longitudinal, vertical and lateral coordinates in that order - changing them moves where the effect emitter is located on the plane model - normally behind the engines. EXCEPT that in FS2002 (don't know about 2004) the vertical coordinate has no effect (it's a 'feature') so you have to change the vertical location by changing the Y-offset value in the .fx file - which you'll have learned how to vary by reading the SDK!

Thanks for the help.

When i do it, Í just need to reselect the aircraft and start smoke again.