This is because Runescape runs on a server and Cheat Engine can only change client side values so you can only make it look like you have money that you don't actually have but it won't effect the money itself other than the appearance.
I don't suggest getting a bot or something like that because it will get you banned for a few days or maybe permanently.
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If you have completed the quest you cannot get another.
there is a master code cheat to use the cheats in the action replay with out it the codes wont work
Try putting in the money cheat or fill all motives
i think they acturaly made it so u cant cheat with cheat engine... Thats not true...entirely. Its worked for me a few times. Its difficult and it conflicts with Adobe Flashplayer, shutting down internet explorer. Their are only a few that wont conflict which is the lvling /exp cheat but u cant enter another fight if u leave the university and the infinate helth and energy cheats work well but the nov and credit hacks work but u cant buy anything I think a new edition of spookmq is out. Its like a mechquest browser with hacks
If this is for Monkey madness quest, the person you are looking for is Glough.