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#1
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W126 - Normal hissing or tank purge issue?
I'm just curious - I'm getting a lot of hissing (pressure not vacuum) from the fuel cap when I remove it and the tank is near empty. This is on my 560SEL.
I'm just wondering at what point do I suspect something is amiss? Should I suspect some sort of purge/evap valve? Never really dug to far into the W126 vapor recovery system. How normal is this, and does anybody know of a decent way to test it? Thanks much!
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-tp 1990 300SE "Corinne"- 145k daily driver - street modified differential - PARTING OUT OR SELLING SOON - PORTLAND OR. AREA - PM ME FOR DETAILS 1988 560SEL "Gunther"- 190K passes anything except a gas station 1997 S420 - 265k just bought it with a rebuilt trans. Lovely condition |
#2
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I dont think it has a canister evap or purge valve. you see it on newer cars that had to meet stricter emission standards. It has the cis fuel injection. I get hissing when i open the fuel cap on any gas car. you are releasing the pressure in the tank. Whenever you do a fuel system service on a car you remove the gas cap so the pressure in the tank doesnt bulge the tank
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1986 300SDL, 211K,Dealership serviced its whole life 1991 190E 2.6(120k) 1983 300D(300k) 1977 300D(211k) |
#3
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Hissing!
I think your ride is just pissed at you! LOL!
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1989 300E 2005 Acura TL 2011 Hyundai Elantra Limited Swing hard! Take chances! |
#4
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Hissing!
Seriously, mine does that too on occasion! I was wondering about that too!
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1989 300E 2005 Acura TL 2011 Hyundai Elantra Limited Swing hard! Take chances! |
#5
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The W126 cars have internal vent valves at the top of the fuel tank that control venting to the charcoal canister. Over time these valves jam in the closed position due to deposits from the fuel or condensation in the tank which prevents the proper venting of the tank. On a warm day the pressure can get quite high. To my knowledge there is no way to remedy this short of replacing the tank or somehow adding a vent line to the tank and installing the external vacuum/pressure valve. I had my 380SE tank professionally cleaned with no resolution of the overpressure issue. No bad effects to the car yet. Mark
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#6
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Quote:
this pressure is the reason why you dont overfill a gas tank. the owners manual listed capacity isnt 100% its a 90% to compensate for the pressure
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1986 300SDL, 211K,Dealership serviced its whole life 1991 190E 2.6(120k) 1983 300D(300k) 1977 300D(211k) |
#7
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It's not overfilling that is the problem---it's gummed up/corroded internal vent valves. Mark
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#8
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So the valve is inside the tank and no way to replace it short of getting a new tank or bodging on a secondary vent?
That sux. Hmmmmm........
__________________
-tp 1990 300SE "Corinne"- 145k daily driver - street modified differential - PARTING OUT OR SELLING SOON - PORTLAND OR. AREA - PM ME FOR DETAILS 1988 560SEL "Gunther"- 190K passes anything except a gas station 1997 S420 - 265k just bought it with a rebuilt trans. Lovely condition |
#9
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Quote:
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#10
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Quote:
I was wrong in my initial post about not having a charcoal canister, its located in the engine compartment
__________________
1986 300SDL, 211K,Dealership serviced its whole life 1991 190E 2.6(120k) 1983 300D(300k) 1977 300D(211k) |
#11
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You are correct---there is a vent valve on the exterior of the tank. However, there is also a "vent system, comprising a collecting tray and a tube system" together with "additional check vessels" located inside the tank. See page 47.7 IV-030/3 of the M116.96 and M117.96 engine service manual for a diagram (I don't have WIS so I have to refer to the paper manual). In my experience it is this internal contraption that suffers blockage due to corrosion/gunk and can't, to my knowledge, be cleaned. Mark
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#12
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Quote:
__________________
1986 300SDL, 211K,Dealership serviced its whole life 1991 190E 2.6(120k) 1983 300D(300k) 1977 300D(211k) |
#13
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Here's the picture of what I'm referring to. Does WIS show this system or its elimination? Mark
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#14
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thats for the early w126's but for the orginal poster the file i posted is correct. they made changes to the change over the years
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1986 300SDL, 211K,Dealership serviced its whole life 1991 190E 2.6(120k) 1983 300D(300k) 1977 300D(211k) |
#15
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I hope you are correct for the poster's sake. The change that your picture described was the addition of an additional separating chamber in the splash bowl located in in the sump of the tank to stop gurgling as a result of vapor being returned with return fuel. The original tanks also had a splash bowl in the sump to provide a steady fuel flow when cornering with low fuel. The piping located at the inside top of the fuel tank is to provide a method to separate the fuel in the tank from the fuel vapors that had to be vented above the design pressure. All MB tanks from other models of the era had external expansion tanks to catch overflow and separate the liquid from the vapor. I seriously doubt that pipe 71 in the later fuel tank diagram exits the tank from the top without some mechanism to separate liquid from vapor. Of course this could be definitively demonstrated if tinypanzer would cut his tank apart for us Mark
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