So this guy tried to do a single tank veggie conversion on my friends 1982 MB 300SD and didn't do a good job. So we tore it out to start over again. When we got all the veggie stuff out to return to the guy and hooked the factory tank back up we couldn't even drive 1/2 mile without air getting in the fuel lines. It idles fine but dies on the road. So we did the following:

1) Tightened all the hose clamps on the tank and on the intake and return lines in the front and made sure all the hoses were hooked up correctly (i am sure of this)

2) Tighented the fuel filter and all the fittings.

3) Changed the primer pump.

4) Then we thought the factory tank was somehow screwed up since it was drilled into. So we pulled a tank off of a 300SD off of a car at the junkyard and installed it. Still the same problem, air in the lines.

This thing is driving us crazy. It ran fine before this guy got a hold of it. We were in the process of doing a 2 tank system but we have to figure this out first.

More question:

What is the hose on the other side of the bottom of the tank, not where the intake and return is but something that's hooked up to some plastic thing? Could this cause an air leak?

And what about the IP? If this is bad could it cause a leak?

okay...so we figured out that the benz will run well if you install longer fuel and return lines and run these into a 5 gallon jug of diesel in the trunk... we got it up to 80 on the highway with no hesitaion running on the 5 gallon jug... then took the factory tank up AGAIN and still had the same problem... What is going on here?!? Somebody has to be able to help me out on this on...

Try disconnecting the fuel line from the tank. Plug the hose and pressureize it from the IP lift pump supply side. Put a couple of pounds pressure on the fuel system and check all joints with soap. It doesn't take a very big leak to break the suction and get air in the system. The only place you can suck air is between the lift pump and the tank. All other parts of the fuel system are under pressure.

So then why does the car run GREAT on a 5 gallon plastic tank with hoses bypassing the factory tank...remember,,we switched out tanks on this car and it's on its second one with the same problem with both factory mercedes tanks...but on the 5 gallon tank from autozone the car runs like it's never missed a beat....i'm sure all the hoses are sealed tight, 100% sure...we have checked them and rechecked them over and over again....

and what is the mystery hose that runs on the other side of the tank opposite of the intake and return hoses? Does this have to have fuel in it to function properly?

this is a great car and i'd really like to see it on the road again,,,soon...thanks

oh yeah...and at this time the hoses are unhooked from the factory tank and just inserted in a cheap 5 gallon plastic gas can...the car runs great with this set up....

Sounds like your tank vent may be plugged. That is probably the other line you were asking about over on the other side. Something to check if you can, does the tank have pressure on it after running at idle for a while? Does the tank go wooosh when you remove the cap? This would be a sign the vent is plugged up. May be tough to determine though, as you say the car seems to not want to run at any speed on main tank.

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1961 190Db retired
1968 220D/8 325,000
1983 300D 164,150

the mystery hose on the tank is the vent i believe, just like on the 5 gallon gas tank, there is that little plug, which is the vent, so the as the fuel is used, air is brought into the tank so it doesn't create a suction

#1 Check the the strainer thats in the FUEL TANK.

#2 Install a rear mounted 12 volt fuel pump. Pretty much clears up the the common problem your having running WVO on single tank Benz's

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Matt (SD,CA)

1984 300SD.. White/Chrome Bunts..Green

1997 2500 Dodge Ram 5.9 Cummins 12 Valve 36 PSI of Boost = 400+hp & 800+tQ .. ..Greenspeed

2004 Dodge Ram 2500 4x4 Quad Cab Cummins 5.9 H.O "596hp/1225tq" 6 spd. Man. Leather Heated seats/Loaded..Flame Red....GREENSPEED

Global warming...Doing my part, Smokin da hippies..

Fight the good fight!......

When you hook back to the cars tank, are you using different braided lines? The cloth braided rubber lines are noutorious for leaking air especially on a suction line. If you haven't done so already, replace all the braided fuel lines. The one that goes right into the tank strainer could be your problem.

One thing that I have learned is to do one fix at a time so that when you fix the problem, you know where it was.

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My Truck.. 2007 DODGE, 5.9 Cummins, 6spd stick, 4X4. My car..1977 240D, OTHER WHEELS...1955 VW Oval window bug, European Delivery (Holland) with a 1700cc, 2 barrel, Porsche drum brakes. 1939 WILLYS Pick-up. 1967 Triumph 200cc Tiger Cub. 1976 Honda 550F 4cyl Motor Cycle.

replaced all the lines with new hose when the veg conversion was done... and these are not clogged...if the vent hose is clogged then will this cause air to be drawn into the intake?? and how do you unclog it,,,and what about the little vent valve, should that be replaced too?

also, why would hooking up another tank matter? especially a 5 gallon plastic tank. we are currently driving the car around on the 5 gallon tank with no problem. then when we hook up the replaced factory tank, same problem...

i understand fixing one thing at a time to eliminate things as probems, but it seems like we have replaced everything except the IP. Thanks for the input...

You are pulling air in somewhere between the tank and the lift pump. Even though you have thoroughly checked several areas, you still haven't found the leak. You may have a cracked steel line between the tank and lift pump. Those lines can rust from the outside so some spots are paper thin, they won't leak until someone bends them slightly for some reason and then CRACK.

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'82 300SD - 361K mi - "Blue"

"Good judgement comes from experience. Experience comes from bad judgement."

listen, look, .........and duck.

hooking the 5 gal tank where? in the back seat? let me have a description of the connections. and yeah, when the vent is plugged, the vehicle wants to suck fuel from a sealed bottle. IT WILL LEAK AIR no matter how good you think the lines are.
John

I believe I agree with Matt, sounds like the filter screen in the tank is plugged. But if you changed the tank to a "new" one then maybe not.

Yes, I believe the small plastic piece, on the opposite side, is a filter for the tank vent. I have never been able to confirm this, just deductive reasoning. Maybe some cold vegoil got into the vent and clogged it?

(I wouldn't trust any mod that required drilling into the main tank.)

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Sam

84 300SD 350K+ miles ( Blue Belle )

I had the tank out of my 240d Sunday, spent mother's day getting the fungi out of it. On the passenger side the fuel outlet screws into the strainer that screws into the tank. On the drivers side there are two connections. One is a barbed connection that is hard connected to the tank, that is the fuel return. One that feels loose, actually runs up to the top of the tank and is the fuel vent. The braided hose on mine was seeping, and since I was there I sloshed the tanks, and replaced all of the lines with a kit I got from Diesel Giant.

I had a problem on a TDI VW where I'd get air leaks after replacing the fuel filter. Turned out to be a weak hose clamp. It would drive fine until you parked it overnight, then air would enter the system, and the fuel would leak back to the tank causing a hard start. I put two worm gear clamps on each of the frequently disconnected hoses, no more leaks.

Good Luck, Chuck.

I recall reading somewhere that the newer style priming pump was giving problems on vegoil. Maybe cleaning it and popping on new fuel filters?

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Sam

84 300SD 350K+ miles ( Blue Belle )