In follow up to the long saga regarding my fuel starved 84 300TD wagon....and after a stint in a local garage, which didn't fix the problem. I just cant figure it out. No need to go into the long details....at this point, the crux of the problem is that the car behaves as if fuel starved. Both filters are new. As the car is running, when viewing the fuel flow through the small initial filter (the little one just before the fuel pump) fuel flows through slowly, even when revving the engine. Then the filter will fill up as it should, with only a normal little bubble at the top, then again it will draw down, and bubbles come in from the fuel supply line.....this happens every several seconds.....the net result is a lot of air going into the secondary filter. If I drive it like this, it will start to stall, as if not able to get fuel.

This morning I drained the fuel tank and removed the strainer....no fungus buildup at all. With the tank empty, I used a compressor and blew out the fuel supply and return lines from the engine compartment. No apparrent blockage. Everything seemed fine.

Then, since I had every thing disconnected, I ran the engine with fuel from a jar in the engine compartment, with supply and return hoses in the jar....when running like this, the engine ran great, with fuel gushing through the little filter as it is supposed to do. I then ran a can of diesel purge full strength, since I had everything set up for it. The diesel purge ran very clean, just gushing through the lines, as it should.

So then I re-connected all fuel lines, put 5 gallons of fuel back into the tank, started her up, and the same old thing happens....air bubbles from the fuel supply line, and fuel barely coming in from the supply line. I haven't checked the tank vent, but the same thing happens when the fuel filler cap is off.

I will now go out and check the entire length of the fuel supply line for sources of air coming in....but there are no fuel leaks, and this is actually a New Mexico car with no rust, very clean, so I dont expect to find rusty fuel lines.

Any other suggestions????? I just cant figure it out.

Thanks

Mark

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1984 300TD Wagon, 407,800 mi (current daily driver)
1985 300DT Sedan, 330,000 mi (gone to that great autobahn in the sky)

There has to be air entering the fuel line someplace between the tank and the filter. The air has to be coming from someplace. IMHO, you need to double/tripple check and tighten every connection in that fuel line. I just can't imagine what else it could be.

There are two short hoses that run from the tank strainer to the hard lines. They are directly above the differential. Normally, they are neglected for the life of the vehicle.

This is the likely source of air entering the system.

Obtain two from the dealer and replace them.

And you are absolutatly sure the supply and return lines arnt switched? Have you tried it with the tank above 1/2, full?

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1985 Euro 240D 5 spd 140K
1979 240D 5 spd, 40K on engine rebuild
1994 Dodge/Cummins, 5 spd, 121K
1964 Allice Chalmers D15 tractor
2014 Kubota L3800 tractor
1964 VW bug

"Lifes too short to drive a boring car"

I would put low pressure/vacuum into the line connected to the small fuel filter and plug the other end near the tank and see if it holds.

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82 300D....went to MB heaven
90 350 SDL....excercising con rods

Brian,

I will replace both of those hoses, but wouldnt they be porous and wet if that is where air is coming in.

Added info. I just had the car for a drive...had it up to 90 mph...seemed ok, but then when at idle, same old thing...fuel starved, air bubbled into filter, etc. !?!?!?!?

This really stinks!!! Figuratively and literally with all the fuel everywhere11

Thanks,,
Mark

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1984 300TD Wagon, 407,800 mi (current daily driver)
1985 300DT Sedan, 330,000 mi (gone to that great autobahn in the sky)

Pull the clips that hold the hard line to the body....I bet you got a leak under one of them....a pinhole leak.

__________________
Proud owner of ....
1971 280SE W108
1979 300SD W116
1983 300D W123
1975 Ironhead Sportster chopper
1987 GMC 3/4 ton 4X4 Diesel
1989 Honda Civic (Heavily modified)
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Section 609 MVAC Certified
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"He who fights with monsters might take care lest he thereby become a monster. And if you gaze for long into an abyss, the abyss gazes also into you." - Friedrich Nietzsche

I was tempted to not follow up on this thread, because I am so embarrased...I am a bonehead idiot!!!!! Before I tell you what the problem was, let me just say that last week Sunday night, there was so much air in the system that it wouldnt start, and I just couldnt figure it out, so I brought the car to a mechanic (which cost me $190 to check compression, clean injection valves, check fuel pump, adjust valves, timing) , and rented a car fr the week to get back and forth to work (to the tune of $250). Not to mention, draining the tank, checking the tank strainer, blowing out lines, making a mess in the driveway, making a stinking mess of my clothes (twice), taking all day last sunday and all day today, etc. etc.


Well, I checked the fuel lines under the car and found no leaks. I borrowed a peristaltic pump from work to pump out tank, and at one point, attached both ends of the tubing to the supply and return lines from and to the tank. When I pumped fuel, the tubing was perfectly clear, no bubbles. But when I put everything back together, I still noticed air coming in.

WELL....just prior to going to the parts store to get some new fuel line, I looked at the filter again, and I noticed a little drip of fuel where the hose from the hard supply line connects to the little filter. I got the fuel line, and replaced that section in the parking lot of the parts store....and....as I said before, I am an idiot imbecile bonehead..... the car ran perfectly, with no air coming in.

That little section of hose, had cracks inside where it connects to the filter, and when the clamp was tighted, it deformed the cracks allowing air to come in!!!! Never any leaks though, as pressure is either negative or neutral...never positive on this line, and very little gravity head at that point!!!!!!

While I am in the middle of a real mess in my driveway, I am going out to change the supply and return hoses at the tank!!!

I would like to ask everyone to respond to this by thinking of a better name for me than bonehead idiot!!!!!


In retrospect, the reason why I love these cars is, as I have told many 123 owners, when something goes wrong with the car and you dont know what it is, and you start to think the worst, most often it is something very very simple. Sure enough!!!

Thanks,

Happy Idiot

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1984 300TD Wagon, 407,800 mi (current daily driver)
1985 300DT Sedan, 330,000 mi (gone to that great autobahn in the sky)

Don't beat yourself up. Sometimes fuel system issues, with reduced power are quite complex and difficult to find. With a clamp on the hose, you would not think that it would leak air. But, an old hose can do this.

Be thankful that you didn't chase such a problem for a month and change the IP in the process. Ask BHD about that. That was a breather problem that had nothing to do with the fuel supply.

Just congratulate yourself in finding the problem without spending a ton of money.

Don't beat yourself up, air in fuel problems are some of the most difficult and time consuming to track down.

__________________
1999 SL500
1969 280SE
2023 Ram 1500
2007 Tiara 3200

Proof positive why you should never discount anything because "you checked that already"

__________________
Proud owner of ....
1971 280SE W108
1979 300SD W116
1983 300D W123
1975 Ironhead Sportster chopper
1987 GMC 3/4 ton 4X4 Diesel
1989 Honda Civic (Heavily modified)
---------------------
Section 609 MVAC Certified
---------------------
"He who fights with monsters might take care lest he thereby become a monster. And if you gaze for long into an abyss, the abyss gazes also into you." - Friedrich Nietzsche

New Mexico (all the desert SW) may not get much rust. But it is hell on rubber, paint and plastic. Especially 20+ year old rubber. If it were me, I'd change every piece of rubber in the entire fuel system.
I don't even want to mention the rubber hoses between the fire wall/ engine compartment Did I mention brake lines

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1999 E300DT (131,800) 154,000 Black on Black SOLD

2006 CLK 500 coupe Capri Blue on Grey (zoom,zoom)
47,000mi

04 VW TDI Passat 80,000mi
(Techno)

How to eliminate oil dependency through market-driven approaches.
“We could cut oil use in half by 2025, and by 2040, oil use could be zero,”
The Sound of Diesel Speed
Ode to MB

I still have my original daily driver, now a parts car, with a lot of new/recent rubber (replaced within the last few years) such as all new cooling system hoses, rubber brake lines..etc. Now that you mention it, this stuff is probably in much better shape than the old rubber on my current driver. Good suggestion.
Thanks,
Mark

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1984 300TD Wagon, 407,800 mi (current daily driver)
1985 300DT Sedan, 330,000 mi (gone to that great autobahn in the sky)

WAY TO GO MARK!!!

Glad to hear you've got that behind you. Being an optomist I can add that now you are assured of the condition of several parts of your car (compression, clean injectors, no woes a the strainer, etc.) that you might not have been if you had replaced the offensive bit of rubber first off.

Marks wagon is sweet, not the ordinary rust mobile I see around these parts....

Hip Hip Hooray!

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Rob M
Norwich, VT USA
1980 240D Euro delivery 4 speed manual silver/blue
~160K miles

Rob,
It looks like given the recent snow and tonights forecast, we may be pulling the differential and axles with snow shoes on!!! Oh how I wish I made time for this a few months ago!!!
Mark

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1984 300TD Wagon, 407,800 mi (current daily driver)
1985 300DT Sedan, 330,000 mi (gone to that great autobahn in the sky)