Vauxhall Vectra engine management light :-(

I baught this car a while ago local to my area , it was already fitted with the duel fuel system (petrol/LPG) but this will not work at min as it needs a changeover valve fitting and god knows where to get that from , belive me ive tried all over !!! the problem i do have tho is that the engine managment light is on and stays on , the engine cuts revs at about 4250 rpm and holds back or bounces. i would imadgin that this will be a failsafe mode or limp mode shall we say and it takes 3-4 times as long as long as normal to reach the speeds required , i have tried the pedal test and the paperclip test to fault find the code myselfe but unfortunatley i today have been told that my engine opperating system OB1 or something 1 and the tests only opperate OB2 or whatever 2 system or summatt??? . without having to pay rediculase prices at a garage to have it just looked at what can u recommend ??? oh i even tried pulling the ABS fuse out to drive it and see if it could of been the wheel sensors as this fuse also opperates the traction control too but it still limited at 4250rpm with no change so obviousley not that ! BUT traction cntrl dousent seem to work on or off but not to bothe3rde about that! HELP !!!!!