No pressure in the gas tank anymore???
 

I switched out my fuel accumulator last month ('91 300E) and car started better for a about three weeks then started doing it's good 'ol long start cranks again (cold or hot). I have recently noticed that right after I drive, if I open the gas tank cap, there is no "phewww" sound air pressure release anymore. I have noticed it with an almost empty tank, half tank, and full tank...zero pressure. Is it possible my fuel pumps are leaking even though I can hear the buzzzz sound when turning the key? Anything else I should check? Just ordered a new fuel filter for the heck of it but didn't think that would have anything to do with it.

You do not want a pressurized tank where air sucks in when you open the fuel cap.

I keep reading that over and over and I am still confused.

How so? If you have this, it simply means your pressure relief valve is bad. :)

Well...sometimes I don't explain myself very well...sorry. When I typically take my gas cap off to fill up or put gas in, there is always a pressure release that sucks in air (vacuum?). Kind of like the pressure or noise that is created after the car runs and you take off the radiator fill cap although that is air pushing out. In the case of my gas tank, it is air sucking in as if the tank is pressurized. But lately, there is virtually no pressure or air suck noise when I take off the cap. I read on most posts that it should have somewhat of vacuum pressure taking place...hope that is more clear.

If the tank is pressurized, how can air suck in :)

Vacuum is negative pressure.

Touche.

I must have a fuel or air leak somewhere. Is it more possible that fuel pumps are old and leaking or could it be fuel injectors? I just put in a brand new fuel accumluator which I'm wondering may have caused pump(s) to rupture due to new front flow pressure? Do I even know what I'm talking about here? :) Am I in the weeds?

You are correct. There should be a "vacuum effect".
Check the fuel pump, filter accumulator array and make sure there is no leak anywhere. You will need to get under the car on a hoist or with it on ramps to check it with the engine running.
When you changed the fuel accumulator you possibly may have disturbed something else.
Did you change the filter at the same time? Did you use new copper crush washers on the filter connection?

Or as mentioned - your check pressure valve may have gone bad.

I just found and ordered two new Bosch fuel pumps off Ebay and a filter. I was wondering if I disturbed something too or did not reassemble properly on the fuel accumulator install (but it started great after that for a while!). I'll wait until I get those and then get under and check Again. Maybe I need some new fuel lines too?

Maybe it is just a bad-sealing gas cap. Replace it.

bobf

You got it ..... no need to look for the most expensive part to replace .... if you are smelling gas, especially when you fill up it is definitely the most logical choice...especially since that happened with our 560SEL ...old car...old cap....cheap fix... under $20.