and how important is it? How much difference does it make in the idle and is it worth getting one? Not sure where it goes but I know mine doesn't have one. Just all regular fuel hose. Thanks, JEFF

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1981 240d aka "The rust bucket"

It acts as a damper on the return fuel line. You'll note it pulses, only if you have one, of course, but while the engine is running feel that line highlighted in the pic.
It's expensive, and some folks just use regular line. If you don't have an idle problem, should be OK.

Attached Thumbnails

 

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83 SD

84 CD

That is a nice looking engine compartment. I like the idea of a filter on the washer line.

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Jimmy L.
'05 Acura TL 6MT
2001 ML430 My Spare

Gone:
'95 E300 188K "Batmobile" Texas Unfriendly Black
'85 300TD 235K "The Wagon" Texas Friendly White
'80 240D 154K "China" Scar engine installed
'81 300TD 240K "Smash"
'80 240D 230K "The Squash"
'81 240D 293K"Scar" Rear ended harder than Elton John

It give Jimmy something to smoke...

It's a fuel pulse damper like TooMany said.

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RRGrassi


70's Southern Pacific #5608 Fairmont A-4 MOW car

13 VW JSW 2.0 TDI 193K, Tuned with DPF and EGR Delete.

99 W210 E300 Turbo Diesel, chipped, DPF/Converter Delete. Still needs EGR Delete, 232K

90 Dodge D250 5.9 Cummins/5 speed. 400K

Gone and still missed...1982 w123 300D, 1991 w124 300D

Thanks. Not sure I need that filter there, but I was replacing the entire washer system, (didn't need to, I was bored) and thought what the heck.

Edit, my sprayers were clogged, that's why.
I remember now.

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83 SD

84 CD

My idle is fine sometimes, but rough sometimes. I replaced all fuel hoses including the "cigar" hose, with regular hose. May I ask why this would effect idle quality? I think I still have the cigar hose, perhaps I'll put it back on and see if there is a differance. I must say dampining the return seems a bit odd to me. Perhaps I have worked on Detroits to long..... So any insight to why the return needs it would be apprieciated.

I believe it's to reduce back pressure, but only the MB engineers know for sure. Maybe they needed to justify their existence.

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83 SD

84 CD

There was some talk on some threads about the hose reducing the (chatter noise & vibrations ) of the IP plunger/barrels unloading at the end of the injection strokes.....

Some posts say the European cars do not use the cigar hose and it was used to reduce unwanted vibration feel for American buyers.....

Still kind of a strange, murky, story......I have used several kinds of hoses on the 240D & have not noticed any difference.....

Maybe on a brand new tight diesel Benz the vibrations could be noticed because everything else was smooth with the vehicle being new....
With my now well seasoned and aged 240D the other shakes and vibes probably smother the petty IP unloading pulses....cigar hose or regular fuel line...

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1978 Yellow 300D (The Mustard Toad)
1980 Blue 240D (The Iron Toad)
1989 Grey Mitsu.4WD Mighty Max Pickup (Needs a Diesel transplant bad)

(Open the pod bay doors HAL)

Purpose is to prevent the equivalent of water hammer in metal piping.
The transfer pump is a positive displacement pump and pumps in jerks and is therefore like starting and stopping the flow of water from a faucet perhaps 20 times per second. The result is hammering in the fuel supply and return pipes. This can be objectionable in the noise realm and can do damage to check valves. This damage coming from cavitation erosion.

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Retired Marine Engineer
2005 E320 CDI
1987 300 Turbo Diesel @ 300,000 kM going
1974 240 D 300,K Miles when given away gone
1970 200 D gone
1969 190 D gone

>>The transfer pump is a positive displacement pump

Actually, it isn't a positive displacement pump.

when i changed all of my rubber lines out to synthetic viton lines the cigar hose was replace with the viton 3/8 line and it made no noticeable difference in my idle or vibration.

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• 1993 Mercedes-Benz 400E *146,000 Miles*
• 1985 Mercedes-Benz 300SD Turbo Diesel Biodiesel *SOLD @ 346,000 Miles*
• 1984 Mercedes-Benz 300D Turbo Diesel Biodiesel *SOLD @ 284,000 Miles*

I suspect if your car originally came with one you should have it. I will not go into all the reasons but even mercedes states not to replace it with fuel line. It does serve a valid function in my opinion.

Please explain why the Fuel Supply Pump it is not a positive displacment pump.

The spring in the Fuel Supply Pump is there to return the Pump Piston (which creates the negative pressure and brings in the fuel).
A cam lobe on the IP Camshaft by way of a Roller Tappet and a Thrust Rod Pushes the Piston the piston ejecting the Fuel from the Fuel Supply Pump. The same amount of fuel is ejected every time. Afterwhich, the spring retuns the Piston.
How is this not a Positive desplacment pump?

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84 300D, 82 Volvo 244Gl Diesel

It is a positive displacment pump.

It really isn't a positive displacement pump.

The pumping stroke is when the piston is on its inbound stroke, heading towards the IP. It is being pushed, not by the rod, but by the spring.

The rod only serves to draw the piston back, and draw fuel into the pump body.

Look at the layout of the pipes.

If the lift pump truly were a positive displacement pump, as many incorrectly seem to think, the inlet would be the union closest to the pump, and the discharge would be at the end of the lift pump barrel.

In fact, the pump is more closely described as a (near) constant pressure pump, the pressure being a balance between the weaker [expressed in fuel pressure terms] of the IP check valve and the spring in the lift pump.

The actual volume of fluid displaced by the pump will vary, and the effective stroke of the pump will vary. As more fuel is used by the IP, or more fuel leaks by the check valve, the piston in the lift pump will be pushed further by the spring, and the rod will contact the IP cam sooner, pushing the piston back to the starting position, drawing in new fuel.