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.

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

__________________
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.

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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

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"

Is there a lift pump in that tank had a car one time where the rubber tube that holds the fuel pump on had a split in it that drove me nuts

This car doesn't have a pump at the tank, but he found the problem, it was a small crack in a hose.

I have posted this elsewhere on a thread I started months ago. I have an 84 TD and have the same air in the fuel problem but I have replaced everything between the tank and the fuel pump. I have replace the rubber lines at least twice and checked for interior condition etc. I even used the expensive nitril stuff. I replaced the metallic line even though I could not find a leak in the original one. My fuel tank is dented right at the fuel outlet and I am wondering if any internal damage could cause a leak? What about the vent lines to the expansion tank? My car can run all day as long as I stop for periods of at least 5 minutes but continuous driving results is sever power starving and usually stalling. When the car stops the fuel filter is dry and some times, even vigorous pumping with the new primer pump draws nothing. Waiting for 5 to 10 minutes allows fuel to be drawn again. I have put a hole in the fuel cap to make sure it is not vacuum lock. The problem can happen with a full tank or an almost empty one. I have checked the vent valve and it opens at just the factory spec values. The strainer has been checked several times. The tank was steam cleaned. All lines blown out. Cracks in overflow tank fixed and lines to it replaced but I did not replace the rubber between the tank and the hard lines to the expansion tank thinking that air could not get in there and it will require removing the tank a third time.

Could internal damage in the tank allow air to get into the " false bottom" that feeds the supply to the fuel pump? The car runs fine with a tank on the roof. I have replaced the rubber lines from the tank to the fuel pump 3 times. Is it possible that 1/4" line will just not seal and that I need to get the right metric size? I am using worm clamps and they seem to make a good physical connection that can not be twisted.

I have spent something like 40 hours trying to fix this and had to buy a new car because I could not depend on the good old TD. I love that car and want to fix her. What else can I try?

Test fuel volume from the return hose, use a gallon jug.
Ten seconds engine cranking.
Post the results for further diagnosis.

Added this thread to ShopForum > Do It Yourself Links & Resources > DIY Links by Parts Category
Fuel Delivery:
Diesel Fuel Delivery:




This may save another owner from massive frustration.

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Where is or are the DIY Links by Parts Category .....
I tried the "DIY Links" Tab for the site but did not find this thread relocated.
:EDIT whunter: Corrected post# 18 and added a link to it.
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I did not get notification of new posts so I had no idea there were additional suggestions.

Removing the cap does nothing. I have run without it and had the same problem. I have drilled a small hole in the cap to prevent vacuum lock although the vent valve works fine. Might be some problems with mush ylines between the tank and the expansion tank so I drilled the hole in the cap.

I checked the strainer at the same time that I installed a completely new hard fuel line. The old one looked fine when Icut it in half and ran a fish tape through it. No crud came out. Strainer was quite clean. No fungus.

Running with a tank on the roof it runs great. Ihad posted the results of a crank speed fuel output test at the request of one reader but never heard back whether it suggests that the fuel pump is bad. I had replaced it with one from my parts car early on. At cranking speed with the FIP shut off, it puts out 70 ml in 10 seconds, 140 if the car is allowed to sort of run for 10 seconds while cranking.

I doubt that rubber lines are collapsing because they are all new. I thought of the idea of crud building up at a high spot and falling down in the 5 minute rest period that restores operation but there was no crud in the thank, the lines or the filter.

I also put a suction pump on the line right after the primary filter with a 1 quart trap bottle to watch the flow while I pulled real hard on the pump. I could produce a fast flow without bubbles or any problems so nothing is preventing flow or letting in air until whatever happens when the problem occurs. I had replaced the two lines at the primary filter before doing this so maybe the fact that they were 5/16" instead of 1/4" was the problem all along and it may be solved. Will not know until I drive it 100 miles or so but I still have no confidence that this was the problem.

Again, does anyone think that the expansion tank and the rubber lines to it could be the problem? I don't understand how the expansion tank works. The pcitures in the shop manual do not show where the lines go in the fuel tank or the expansion tank. Can air get into the fuel from the fuel tank to the pump via the expansion tank?

I had a primary filter that had a crack in it along the injection mold line. I did not leak, and the car idled fine. It was running down the road that the issue of fuel starvation made itself known. It was a Purolator filter bought at Pep Boys, and it lasted about a week.

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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