Problem with my 126. Can you help?

[revray]

Aloha from Hawaii,

I have two 300SD's... a 1980 (W116) and a 1982 (W126). I have run both cars with no modifications on 100% biodiesel (my own home brew) for just over 3 years. The 116 has performed without incident (have changed fuel filters a few times). The 126 has also run pretty well, until recently.

It idles and drives well for about 15 minutes, and then sputters and dies. Thinking that there was an obstruction in the fuel line, I disconnected the fuel line coming from the fuel tank at the engine compartment, blew it out with compressed air, and reconnected the fuel line. The car would start right up, but then sputter 15 minutes later and die.

Believeing that maybe some of my fuel hoses were deteriorating from the inside, I emptied the fuel tank and changed everything... both hoses at the tank (including a new tank screen), both hoses in the engine compartment, new fuel filter, and all of the injector return lines. I primed the engine, started it right up, and let it idle. About 15 minutes later... it sputtered and died.

Does anyone have a diagnosis?

Thanks in advance

[kerry]

Try running it on a separate container of fuel hooked up to the feed and return lines in the engine compartment. Those symptoms are typical of a plugged tank vent stopping the flow of fuel and possibly a plugged tank screen. Running it on a separate fuel supply could confirm or deny a tank problem.

[bustedbenz]

Tank screen has already been replaced. Just to rule out all possibilities, run it with the fuel cap off the tank just for grins. If it doesn't die, then it's pulling a vacuum on the fuel tank and the vent line is plugged.

[TX76513]

Well what's left, IP and Injectors

[Diesel911]

Originally Posted by kerry

Try running it on a separate container of fuel hooked up to the feed and return lines in the engine compartment. Those symptoms are typical of a plugged tank vent stopping the flow of fuel and possibly a plugged tank screen. Running it on a separate fuel supply could confirm or deny a tank problem.

You can also just remove the fuel tank cap allowing the fuel fill pipe to act as the tank vent.

[daw_two]

Originally Posted by kerry

Try running it on a separate container of fuel hooked up to the feed and return lines in the engine compartment. Those symptoms are typical of a plugged tank vent stopping the flow of fuel and possibly a plugged tank screen. Running it on a separate fuel supply could confirm or deny a tank problem.

tank vent????
Could this explain why my tank always has pressure built up in it?
Where might the vent be???
I'm guessing "Elegant Madame's vent" might be plugged.

[toomany MBZ]

Originally Posted by daw_two

tank vent???? There is one.
Could this explain why my tank always has pressure built up in it? Correct, not supposed to.
Where might the vent be??? Located under car near drivers side rear wheel, a bell looking thing, connected to a vent hose.
I'm guessing "Elegant Madame's vent" might be plugged.

I ran a coat hanger wire as far as I could, I did not have any obstruction. When you open the fuel tank lid, there should not be any sound. I have an exploded view of the vent line, yet it shows only from the bell thing to the tank, has got to lead to metal line in the tank, somewhere.

[revray]

Would a faulty/inoperative primer pump explain the problem?

Thanks

[daw_two]

Originally Posted by toomany MBZ

I ran a coat hanger wire as far as I could, I did not have any obstruction. When you open the fuel tank lid, there should not be any sound. I have an exploded view of the vent line, yet it shows only from the bell thing to the tank, has got to lead to metal line in the tank, somewhere.

Okay....so WHERE is the vent???

sorry for hijacking the thread.....

[vstech]

Originally Posted by daw_two

Okay....so WHERE is the vent???

sorry for hijacking the thread.....

the red text in the quoted response tells you where to look. drivers rear wheelwell, bell shaped contraption. probably covered with gook...

[daw_two]

Thanks for pointing that out.....see what happens when the answers are intermingled with the questions? I completely missed it. Going to do that tomorrow night as soon as the kids are in bed.

Thanks!!!

[Diesel911]

You can remove the fuel tank fuel (gas) cap to test if the tank vent is plugged. If it runs OK without the cap on you will know that the fuel tank vent has a problem.

[charmalu]

I had this same problem with my 123. I came home late one night, and when I got out of the car I could hear this real faint air sucking sound near the L/R tire. looked under the car, and little bell shaped vent was making the noise.
The next day got under the car and cleaned out the dirt etc... has woked fine ever since. I think there is also a check valve between it and the metal line.

Had the same problem with my 82 Datsun Diesel pu. the tank would be pressurised when I removed the cap. removed the check valve and all fixed.

Charlie

[dougk]

Originally Posted by revray

Would a faulty/inoperative primer pump explain the problem?

Thanks

It might account for the problem. Also, you have been running b100, check to make sure all you lines are okay and none of them are sucking air because the engine sputtering and dying is a good indication of either the vacuum issue above or air getting into the system. Also, check lines for buildups inside as I had some junk that didnt get trapped in the filters and partially plugged a line that continually gave me problems.

Good Luck

DK

[toomany MBZ]

Originally Posted by charmalu

I think there is also a check valve between it and the metal line. One did not show up on my exploded view.


Charlie

I try to remember to use a different color type and bold also, the better to stick out you understand.