1995 E300 W124-Om606 pressure in fuel tank - Page 3 - PeachParts Mercedes-Benz Forum

funola · #31 01-23-2017, 12:20 PM

Quote:

Originally Posted by packerfan

No I did not find it yet and yes I did open the link (thank you for that) I can't see much from laying on my back looking up. I may have to take it to a garage that has a car lift.
Last night I filled the tank with fuel and stopped before it started coming up the fill pipe then I put the fuel cap on and backed it off some which has solved the engine stalling problem. This morning I started the car and let it warm up for about five minutes and noticed a 24" diameter puddle of fuel on the driveway, I looked under the car and could see fuel dripping from a hose that I think is an over flow tube that runs up to and under the fill cap.
I can understand that a clogged vent would cause this because the pressure has to escape from somewhere and I do plan on inspecting the vent but sure am having a hard time figuring out what is causing the pressure.
I ordered a new lift/feed pump and I doubt that is the problem but I thought it might be worth a try.

The tank vent intake is at the very top of the tank where there is always an air pocket. Even with a full tank, the air pocket should still be there and fuel should not be coming out of the vent on the bottom of the car. I don't understand why the vent is so hard to find. Coming out of the bottom of the tank should be 3 lines, 1st one is fuel supply, 2nd is fuel return, both go up to the engine, 3rd is the vent. Per the diagram, it is somewhere between the 2 rear wheels.

This diagram says the vent system has been modified as of 10/88. Can't tell if the vent on the bottom of car has been eliminated or not.
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funola · #32 01-23-2017, 12:28 PM

When he says fuel spills all over him when the fuel cap is removed, we have to believe him, that he is not mistaken it is indeed pressure and not vacuum.

Diseasel300 · #33 01-23-2017, 01:21 PM

Quote:

Originally Posted by funola

When he says fuel spills all over him when the fuel cap is removed, we have to believe him, that he is not mistaken it is indeed pressure and not vacuum.

Fuel spraying out is indeed possible if pressure is built up in the system. My SDL did this with a clogged tank vent and a new gasket on the filler cap. I had 2 issues working against me: air in the system (leaking fuel thermostat) and excessive heat (fuel thermostat not going into bypass).

Together with the clogged tank vent, it would send out a healthy puff when the cap was removed and spray fuel all over my hand.

Fixing the air ingress, bypassing the fuel thermostat, and clearing the vent solved my problem.

funola · #34 01-23-2017, 05:42 PM

If the fuel heater is not shutting off, heated fuel is continuously sent back to the tank. With a clogged tank vent, pressure builds due to expansion of the heated fuel.

I'd suggest putting a test light across the fuel heater. If it's always on, that could very well be the cause of the pressure.

Diseasel300 · #35 01-23-2017, 09:04 PM

The fuel heater thermostat on an OM603 is mechanical, and the heater itself is just pipes running along the coolant lines. The 606 may be different. I was using my car as an example. In my case, it never gets that cold here, I just bypassed it (not interested in shelling out money for a part that won't see any real use).

But yes, the air ingress + expansion from excessive heat + clogged vent = pressure + fuel spray. Fixing the air ingress, bypassing the fuel heater, and fixing the tank vent = no drama when tank cap removed.

funola · #36 01-23-2017, 10:02 PM

If the fuel heater is coolant heated, try bypassing it and see if the pressure issue goes away. Do not ignore the clogged tank vent once you solve the pressure issue..... the tank will collapse from vacuum.

spark3542 · #37 01-24-2017, 12:34 PM

On my '97 606 years ago I had a clogged vent. Solved by simply blowing a burst of compressed air into the vent. This was after my tank collapsed however. My collapse was minor, but it took about 3 gallons of capacity out of the tank. Vacuum is powerful.

spock505 · #38 01-24-2017, 12:55 PM

This is not directly related to the OP issue, but has some overlap, thought funola would find it interesting too.

First post by Alan.

OM606 fuel supply issues

funola · #39 01-24-2017, 01:36 PM

Quote:

Originally Posted by spock505

This is not directly related to the OP issue, but has some overlap, thought funola would find it interesting too.

First post by Alan.

OM606 fuel supply issues

I have read that article and he (Alan) was astute in his observations. Fuel hoses must be appropriately sized throughout the system for the highest fuel demand. When they are too small, it causes restrictions. Dissolved air in the fuel (there is a small precentage of air) can be sucked out of it by a strong lift pump and bubbles in fuel is created along with fuel starvation.

spock505 · #40 01-24-2017, 01:42 PM

Quote:

Originally Posted by funola

I have read that article and he (Alan) was astute in his observations. Fuel hoses must be appropriately sized throughout the system for the highest fuel demand. When they are too small, it causes restrictions. Dissolved air in the fuel (there is a small precentage of air) can be sucked out of it by a strong lift pump and bubbles in fuel is created along with fuel starvation.

I'll have to measure the fuel supply on my OM606.962 (turbo), when you put the hammer down it really shifts, never seen any air bubbles at all.

funola · #41 01-24-2017, 01:48 PM

Quote:

Originally Posted by spock505

I'll have to measure the fuel supply on my OM606.962 (turbo), when you put the hammer down it really shifts, never seen any air bubbles at all.

How are you going to measure? One way to see if you have bubbles or not is rig a video camera on a clear return to tank line when you floor the throttle going up a steep hill.

spock505 · #42 01-25-2017, 02:00 AM

Quote:

Originally Posted by funola

How are you going to measure? One way to see if you have bubbles or not is rig a video camera on a clear return to tank line when you floor the throttle going up a steep hill.

Only a basic measurement (OD) of fuel/return pipes. Pretty sure they are the same though, as the other fittings fuel heater, plastic pipes ect. (which are the same) would cause a further restriction up the line.

packerfan · #43 01-28-2017, 10:05 PM

Quote:

Originally Posted by funola

Have you found it yet? As Alec said, it should be under the car. Did you open the link I posted? The diagram shows the tank vent routing clearly.

I finally got a chance to find what I think is the tank vent.If what I found is correct, it is much smaller than I expected. A small soft rubber bell shaped boot about the diameter of a penny and open at the bottom and about 1 inch long.
It appears to be clean, (no dirt whatsoever) kind of orange colored with a small silver hole in the center?
How do I remove it to check if it is clogged?

spock505 · #44 01-29-2017, 03:17 AM

Only real way is to remove the tank (weather permitting).

Sometimes it's the tank lining which falls away causing the blockage, there's also other bits in there which may benefit from a clean such as plenum chamber.

It's not uncommon for tank strainers to look something like this, my 210 was identical prompting tank removal and cleaning.

The other thing which can cause similar problems, is diesel bug, again best option to get everything cleaned properly with fresh fuel.

sloride · #45 01-31-2017, 11:35 AM

FYI while going through my 95 owners manual E300D page 124
(1) Fuel Supply To add fuel turn cap to the left and hold on to it until possible pressure in tank has been released, then remove the cap. Failure to do so could result in personal injury.
So positive pressure is not uncommon. I had thought that the vent was to let in air to replace the fuel that has been used.
Not any help for a stalling issue but figured i would throw that in.