What model is the Furuno? If it's what i think it is it's one of the best units out there. You could have a weak transducer, or your trying to run them all at the same time. That won't work usually. Give furuno a call and tell them your issues & if you don't have one down load a manual on there site for the model you have. Might save ya alot of $ for a good unit you already have.