1991 420sel. Can someone explain to me the functions of of both of these items and how are they related? I know where the pressure regulator is located, but where is the accumulator?

The Fuel Accumulator is located next to the Fuel Pump and Fuel Filter.

From another site:

"Often times the noise you hear can be a droan or a moan which is caused by a faulty fuel accumulator. It's a component that maintains constant pressure in the lines. It can either be leaking fuel or the inner diaphragm spring could be broken".

Fuel accumulator
The fuel accumulator maintains the pressure in the fuel system for a certain time after the engine has been switched off. When the engine is running it serves to deaden the noise of the electric fuel pump. After the engine has been switched off, the fuel accumulator maintains the pressure in the fuel system in order to facilitate re-starting, particularly when the engine is hot. The design of the accumulator housing is such that it deadens the noise from the fuel pump when the engine is running. The interior of the fuel accumulator is divided into two chambers by means of a diaphragm. One chamber serves as the accumulator volume for the fuel, the other chamber contains a spring. During operation the accumulator chamber is filled with fuel. This causes the diaphragm to bend back against the force of the spring until it is halted by the stops in the spring chamber. The diaphragm remains in this position, which corresponds to the maximum accumulator volume, as long as the engine is running.


1. Spring chamber
2. Spring
3. Stop
4. Diaphragm
5. Accumulator column
6. Fuel inlet/outlet
7. Connection to the atmosphere
a) Empty b) Full

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1993 190E 2.3
2001 SLK230
1971 LS5 (454) Corvette Convertible

Thanks and great info.
One of the things that I noticed is that after my car has sat for a time, normally overnite, it may not be pressurized any longer. I had gone to a Pull a Part several times to get spare parts and when I loosened the supply line to the CSV, it was still pressurized even after sitting for months and squirted gas out. Another car did the same thing. I had done this to my own car several times and that line is not. I have pressure when I turn the ignition to on and the CSV hose sprays like crazy. So my question is "Could this be a faulty accumulator. I don't have gauges to do any pressure testing. Other than a hard start (a few engine spins), the car runs fine. Warm starts are no problem at all.

The problem that I'm having is that sometimes during warm starts I get a moaning, gurgling sound in the Fuel Pump area. It starts up fast, but it sounds like fuel is going into the gas tank and the fuel pressure is low for a couple of seconds, then it smooths out. I need to do the 'hose pinch' test at the rear of the Fuel Accumulator to verify my theory when the engine is warm and it does what I stated.

I'll bet your start problem isn't fuel related.

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1993 190E 2.3
2001 SLK230
1971 LS5 (454) Corvette Convertible