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  #1  
Old 07-01-2005, 10:33 AM
GoWolfpack
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VERY Sluggish on 2nd half of Tank

Hi All,
About 2 months ago, I bought a 1985 300TD that had been sitting in NC for sometime. Everything is fine with this car until I get to about 1/2 tank of fuel.

Then she hesitates and runs so sluggishly it's actually dangerous to be in traffice. Thinking I may have bad fuel or water/algae, etc. I manager to limp to a service station and filled her up with diesel. After idling for a while, all seems well.

Now this morning she did it again. Valves have been adjusted and when everything's kosher, she runs like a little swiss watch.

Does it sound as if I have some gunk in the tank that needs to be removed and then clean the tank?

Any ideas/suggestions greatly appreciated!

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  #2  
Old 07-01-2005, 10:36 AM
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Join Date: May 2002
Location: Blue Point, NY
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The SDL just did this on the last tank. It lost about 50% of the available power when I got down to the last three gallons.

Funny thing about it was that it took about 100 miles of running, after the tank was filled for the power to completely return.

In fact, I can't be certain that it has fully returned because I typically measure its performance against a specific grade in CT. It should be able to hold 70 mph on the grade if it is providing the proper horsepower.

We'll see........

It's a strange deal, I'll say that for it. Can't be fuel filters, AFAIK, because they are not self-cleaning as the vehicle is driven.
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  #3  
Old 07-01-2005, 10:51 AM
Old Deis
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First thing I would check is the ruber, or fabric fuel line that is attached to the steel fuel line on one end and to your fuel filter on the other end. Take it off and check it for leaks. They can leak air into the fuel, and still not leak fuel out. If it sucks air in, will cause a big time power drop.
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  #4  
Old 07-01-2005, 11:16 AM
GoWolfpack
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Quote:
First thing I would check is the ruber, or fabric fuel line that is attached to the steel fuel line on one end and to your fuel filter on the other end. Take it off and check it for leaks.
Thanks for the info--but wouldn't I experience a power loss that is not constant?

This firt happened to me a couple of weeks ago (when I was down to about 1/2 a tank) and once I filled it back up, she would motor down the highway at 75mph with the best of them! But this morning--same old thing.
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  #5  
Old 07-01-2005, 11:32 AM
LarryBible
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I would start by putting some bio gard in the tank.

Good luck,
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  #6  
Old 07-01-2005, 12:22 PM
GoWolfpack
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Thanks Larry,
Where should I be able to buy biogard?
Thanks in advance.
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  #7  
Old 07-01-2005, 12:45 PM
Old Deis
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I had a signigicant power loss with my 78 last year, it was intermittant. After treating the fuel, running diesel purge, and checking the timing, it noticed the fuel line there was moist. Ran my hand over it and it smelled of fuel.
Took it off and looked ok, but could blow through one end with the other plugged and it would leak air easily.
Just replaced and the problem went away quickly. I am guessing that it was intermittant with low fuel in the tank, and with different temps. With a full tank fuel will usually pour out the line, not so when running on empty.
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  #8  
Old 07-01-2005, 12:48 PM
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Quote:
Originally Posted by GoWolfpack
Thanks Larry,
Where should I be able to buy biogard?
Thanks in advance.
Are there any boating supply places nearby? THats where I got Biobor from.
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  #9  
Old 07-01-2005, 12:52 PM
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Remove the big ring nut holding the fitting in the tank base....it should have a tall screen inside...need nearly empty tank to do this or a large container for the fuel..



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  #10  
Old 07-01-2005, 12:53 PM
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rusty fuel lines

this same thing started to happen to me about a year ago and after looking in both the engine compartment and the fuel tank I gave up for a while and just kept my tank as full as I could. but it steadily started to get worse until i could barely drive anywhere, regardless of the level in my tank. I ended up finding out the fuel lines from the tank to the engine were rusting out. with a full tank there was enough pressure in the lines from gravity to not allow any air to suck in, but they sucked air at lower levels of fuel.
I did not have to replace the entire length of the fuel lines, I just cut out the rusted part and replaced it with some flexible fuel hose (aprox three feet total). this did the trick. the most common place for this rust is in the rear end above the sub frame where salt and debris hangs out, you can check this by looking around the driver's rear tire for fuel drips- these drips started very slowly on mine so they were hard to find. it helps to clean the fuel line off with a rag so it will encourage the fuel to glide down the line and drip on the ground just infront of the rear tire. if this ends up being the problem check your sub frame for rust too-very dangerous situation if they start to rust through.
as I have been writing this I have also been thinking that you should check your overflow tank in the spare tire compartment and make sure that is not leaking any fuel there or any of the hoses from the overflow tank to the main tank. I could see this sucking air at certain levels of fuel while not sucking air at others.
to test if your system is sucking air, the next time you lose power pop the hood and inspect your fuel filter if it is not very full that could be an indication it is sucking air. with the engine running vigourously pump your primer pump and quickly drive a mile or two to see if it fixes the problem temporarily, if it is really idling hard pumping the primer pump should immediately smooth out the idle as well.
After I diagnosed my problem and drove to the shop to buy parts I ended up having to pump the primer pump every couple of miles just to get down the road (they are back roads, so it was o.k. to drive 10 miles an hour with the pedal floored!)
when I was checking my fuel filter it had little black flecks in it, which I found out were tiny rust flakes coming off of the inside of the fuel line. this was fixed when I replaced the bad section of fuel line so that might also be an indicator
anyway hope this helps, if it is not caused by sucking in air I don't know what the problem could be.
cheers
Scott
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  #11  
Old 07-01-2005, 01:25 PM
GoWolfpack
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Hi and thanks all for your posts.
I checked the prefilter and there is quite a bit of algae looking crud in there. I just put a new prefilter and filter on a few weeks ago, so there must be quite a garden in my tank!

I have the new style primer pump and pumped it a few times. Noticed there were little air bubbles coming up from the forward end of the prefilter. Does ths suggest air in the line?

Looks like so much gunk in the prefilter that it is prohibiting a good flow of fuel.
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  #12  
Old 07-01-2005, 01:35 PM
LarryBible
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From what you describe, you do need to kill the algae, but there are others here with some experiences that I have not dealt with. It makes all the sense in the world that a leaking line could be the culprit.

Look at all the lines under the hood and all the way back to the tank. A leaking line should have wet fuel around it. You might even be able to smell the culprit.

Good luck,
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  #13  
Old 07-02-2005, 08:40 AM
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GO,

Remove the rubber fuel line from the fuel tank where it connects to the steel fuel line.

The fuel should come out in a steady stream about 1/4 inch in diameter. If it doesn't, the strainer in the tank is plugged, probably by fungus. You then have to remove the strainer and clean it.

If the strainer has a brown silicone rubber like substance on it, you have fungus in your fuel system. Only a fungicide like Biobor will kill the fungus. You can clean the strainer with compressed air but if you don't kill the fungus, it will plug the strainer and filters again.

P E H
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  #14  
Old 07-02-2005, 10:59 AM
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Quote:
Originally Posted by GoWolfpack
Hi and thanks all for your posts.
I checked the prefilter and there is quite a bit of algae looking crud in there. I just put a new prefilter and filter on a few weeks ago, so there must be quite a garden in my tank!

I have the new style primer pump and pumped it a few times. Noticed there were little air bubbles coming up from the forward end of the prefilter. Does ths suggest air in the line?

Looks like so much gunk in the prefilter that it is prohibiting a good flow of fuel.
The little bubbles DO indicate a severe flow restriction. It also indicates that your filter - hose connection is poor and is allowing air into the fuel system.
I recommend that you replace the prefilter and the short hose between the prefilter and the lift pump and treat your fuel tank to counteract the infection. You may find that you can get cheap chinese fuel filters for 50c or so. Adding one of these before the MB prefilter will allow you to replace these filters cheaply, while retaining the protection of the MB prefilter.
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  #15  
Old 07-02-2005, 11:47 PM
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GO,

If the MB engineers thought you needed cheap Chinese fuel filters in your car, they would have added some when building the car.

I had a fungus contaminated fuel system. After treating the fuel sustem with Biobor, I had to only change one inline filter when it plugged up. I suggest you check the fuel strainer and treat your fuel system with a fungicide if you find fungus on the strainer. But you dn't need to add extra fuel filters.

Replace any fuel lines you find to have leaks. Putting a small amount of pressure in the fuel tank (you have to block the tank vent), not to exceed 1 PSI, will show where any leaks are in your fuel lines.

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