ed ▁spark - ign ition ▁engines ▁have ▁int ake ▁manifold ▁" v acu um " ▁due ▁to ▁the ▁int ake ▁restriction ▁of ▁car b ure tor ▁vent ur is ▁and / or ▁thro tt le ▁" but ter f lies ". ▁And ▁" v acu um " ▁is ▁used ▁to ▁properly ▁t une ▁car b ure t ors ▁or ▁fuel ▁injection ▁systems ▁and ▁ign ition ▁timing ▁as ▁well ▁as ▁determine ▁engine ▁condition ▁and ▁diagn ose ▁engine ▁mal functions , ▁mis - ad just ments ▁and ▁fail ures . ▁engine ▁problems ▁result ▁in ▁" v acu um ▁le aks " ▁or ▁levels ▁and ▁the ▁intensity ▁and ▁timing ▁and ▁duration ▁of ▁constant ▁or ▁inter mitt ent ▁vac u um ▁level ▁depart ures ▁from ▁normal are ▁used ▁to ▁diagn ose ▁internal ▁engine ▁problems ▁without ▁engine ▁dis assembly ▁and ▁ins pection . ▁Such ▁depart ures ▁are ▁generally ▁far ▁too ▁small ▁to ▁make ▁infl ated ▁" absolute " ▁vac u um ▁pressure ▁use ▁practical ▁or ▁even ▁possible . ▁ ▁Therefore , ▁" g au ge ▁press ures " ▁independent ▁of ▁atmos pher ic ▁pressure - infl uen ced ▁" absolute " ▁press ures ▁are ▁preferred ▁for ▁monitoring , ▁tun ing ▁and ▁diagn osing ▁engine ▁operation ▁and ▁performance ▁when ▁mechanical ▁fuel ▁systems ▁and ▁gau ges ▁are ▁in ▁use . ▁Only ▁electronic ▁engine ▁control ▁and ▁monitoring ▁systems ▁used ▁in ▁conj unction ▁with ▁" man if old ▁absolute ▁pressure ▁sens ors " ▁capable ▁of ▁replacing ▁vac u um / boost ▁gau ges ▁and ▁tur bo charg ing ▁which ▁is ▁capable ▁of