Examine the picture for me guys. Why would the line be bleeding back down after a day or two? Seems to me the lift pump would have some sort of anti drain back valve, but no clue. Lift pump is original to the vehicle to the best of my knowledge. I have never replaced it since my purchase in 2005. Just a few documents from the PO for a starter and glow plugs. It has had the head off before.

My car will not stay idling unless I keep the throttle down some. I have it running off a separate fuel can for testing to eliminate the fuel tank and screen. Spin on and inline are new. Fresh fuel too.

Recently replaced the delivery valve seals. Fuel comes out of all six IP lines when it does catch itself and idle...but when it does, the idle is galloping. Not correct.

I feel like I a missing something simple.

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I'm not a doctor, but I'll have a look.

'85 300SD 245k
'87 300SDL 251k
'90 300SEL 326k

Six others from BMW, GM, and Ford.

Liberty will not descend to a people; a people must raise themselves to liberty.[/IMG]

I would think you have a partial faulty lift pump. There is no check valve inside but a spring loaded disk. The spring may have broken or the disk broke. It is easy to remove and check. Remove the 2 10mm nut and pump it by hand and check suction on inlet and pressure on outlet. You can also open up the lift pump and check the valve.

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Not MBZ nor A/C trained professional but a die-hard DIY and green engineer. Use the info at your own peril. Picked up 2 Infractions because of disagreements. NOW reversed.

W124 Keyless remote, PM for details. http://www.peachparts.com/shopforum/mercedes-used-parts-sale-wanted/334620-fs-w124-chasis-keyless-remote-%2450-shipped.html

1 X 2006 CDI
1 x 87 300SDL
1 x 87 300D
1 x 87 300TDT wagon
1 x 83 300D
1 x 84 190D ( 5 sp ) - All R134 converted + keyless entry.

I had this issue earlier this year. Turned out to be heavily worn O-ring seals in the lift pump. You can read about it in the thread I made on the topic here:

OM603 602 601 Lift Pump Re-Seal (O-Rings)

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Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

The lift pump has two check valves and your lift pump is probably very old. A simple re kitting is cheap and easy. Both check valves face the direction that blocks reverse fuel flow. I expect that accumulated dirt over the years on the valves and seats. Is a contributor to increased leakage as well.

These may be the best fuel pumps ever designed in comparison to the majority of mechanical pumps. But at the same time nothing lasts forever. Thankfully they are cheap and pretty easy to rebuild yourself.

There is a reliability issue and other things to be gained by a general check and reconditioning. Where needed on these now older fuel systems. The better you get to know them the easier to solve any issues that arise.

Actually with them put in good condition there may also be fewer issues that arise as well. Remember the system cannot back drain either if truly tight and sealed going forward from the lift pump. Air has to get in somewhere.


A non sealing properly relief valve for example is a possible source. It for example could still function well enough for the intended purpose but still have some leakage existing. Again just dirt buildup over the years and yours is easily removed. Taken apart and cleaned. There is even a tool out there to clean up the seat the sealing ball rests on.


You can balance a full glass of water on any of my diesels. without spilling a drop. If you want to also do this when they are running it is best to freeze the glass of water first.

Newer Lift Pump Repair with Disc Valves
95 E300D (606.910) Fuel Lift Pump Rebuild Question - PeachParts Mercedes ShopForum
606 Fuel/Lift Pump Rebuild
OM606 Fuel Pump Rebuild - PeachParts Mercedes ShopForum

You need to find the repair kit for your particular Lift Pump.

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84 300D, 82 Volvo 244Gl Diesel

Killer!

Thank you for the responses and reaffirming my thoughts.

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I'm not a doctor, but I'll have a look.

'85 300SD 245k
'87 300SDL 251k
'90 300SEL 326k

Six others from BMW, GM, and Ford.

Liberty will not descend to a people; a people must raise themselves to liberty.[/IMG]

Fixing the Fuel Supply/Lift Pump is the best way to go because it fixes the other issues that might come up from not having it work correctly.

An alternative way to keep the Fuel from migrating back to the Fuel Tank is to put a one way check valve in the fuel inlet hose or tubing.

The ones in the attached picture came up when I searched eBay for "fuel line check valve".

Don't know if the ones shown will hold up if diesel fuel is used or not. Need to ask the seller for that info.


I would have posted be for but had no pics.

Attached Thumbnails

 

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84 300D, 82 Volvo 244Gl Diesel

New unit installed, manufactured in 2013... old was from 1986. Air in system seems gone, still will not idle. Did drain the oil, had fuel in it.

Off to pop test my injectors and go from there. Also, will replace the return line banjo fitting as the spring is probably dead hurting rack pressure.

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I'm not a doctor, but I'll have a look.

'85 300SD 245k
'87 300SDL 251k
'90 300SEL 326k

Six others from BMW, GM, and Ford.

Liberty will not descend to a people; a people must raise themselves to liberty.[/IMG]

Number one on the diagram is the O-ring that would cause the Fuel to leak into the Fuel Injection Pump and from there into the Oil.

Attached Thumbnails

 

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84 300D, 82 Volvo 244Gl Diesel

Gotcha. I also have a new, OEM oring for the fuel thermostat to toss in tomorrow.

__________________
I'm not a doctor, but I'll have a look.

'85 300SD 245k
'87 300SDL 251k
'90 300SEL 326k

Six others from BMW, GM, and Ford.

Liberty will not descend to a people; a people must raise themselves to liberty.[/IMG]