ive had all this with mine lol..... been there done that and bought the fukin t-shirt!! low oil pressure can be a whole load of things....... the main thing that will really make it low on tick over will be worn main bearings/crank - any thing over about 0.076mm clearance in the bearings and you will get it (low oil pressure that is), could be blocked oil ways in your head? in a cosworth yb you should be using a thickish oil (ford in there manuls say 20w50!) mobil 1 15w50 you should be using or something equivelent unless you warrant a reason to run thin oil? how old are the followers? and you want to be using genuine ford ina's or equivelent as you can get cheap shite one for about £40 odd quid and they rattle and tap.... also you idealy want to run a high pressure oil pump weather its a std engine or not as imo i know the std 2wd pump runs quite low on tick over... what is the turbo like as if the bearings are worn in that you can lose a lot on tick over......