More than you probaly wanted to know but an accumulator as used in this sense is, by definition, a hydraulic term. Commonly used in hydraulic systems (your fuel system is a hydraulic system), accumulators are devices used to store (or accumulate) pressure when the main pressure pump is off. They do this in many ways but are usually a spring loaded volume that pressurizes the fluid in the system. The system requires chceck valving or other means to make it tight or the accumulator won't do it's job effectively Your fuel injection system needs to remain pressurized after the fuel pump stops to avoid vapor formation and hard starting. The accumulator does this for you. I'll leave it to others to describe exactly how it does that but suffice to say it works in conjuction with other check valving and seals in your fuel system to keep the fuel pressure at a certain value. There is a spec for this "rest" pressure in your service manual, along with the minimum time the system should hold it for. Btw, don't ever open any hydraulic accumulator up without restraining it, depending on the diameter of the diaphram or piston there is tremendous energy in the srping. The bigger the system pressure, the bigger the diameter of the unit or strength of the spring needs to be. (Force = Pressure x Area in fluid engineering.) I've seen a Bosch unit that, when cut open on a lathe, fired the internal parts and spring right through a wooden door. It has a serious spring in there, for those who've seen the inside of the Bosch unit you know what I mean. --- In dmcnews@xxxxxxxxxxxxxxx, id <ionicdesign@xxxx> wrote: > i have a stupid question and i should know this but what does a Fuel Accumulator do > exactly? > > mark