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  #1  
Old 10-24-2005, 03:27 PM
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Exclamation HELP! This fuel gage drives me insane!!!

Before the forum went down I posted this thread and got one response that help a lil bit. It is about the fuel gage on my 87 300D.
I replace the fuel sending unit about 3 weeks ago.
When I feel up the tank everything is fine until about half tank left. When the tank reaches about 1/4 sometimes, and I DO MEAN SOMETIMES only when I turn the key to the glow plug position before starting it shows me the right amount of fuel 1/4. Car starts and the fuel indicator needle moves very slowly towards the half tank, after about 10 minutes it shows half tank or just a lil bit below that, and doesn't move. Sometimes it moves, slowly towards the 1/4 mark again. Stop the car after 1 hour or so of driving turn the key to the on position, it shows me half tank. Start the car, it jumps to the 1/4 mark.
Someone here advise me to put 1 gallon of veggie oil in the tank. As a parenthesis it was very funny the way people in the gas station looked at me putting one gallon of pure veggie oil in the tank, since I have no emblems on the trunk indicating a diesel. Anyway... The gage improved a lil bit, it shows more accurate but now it moves very slowly between half tank and 1/4 marks for couple of minutes. I was happy since all day yesterday it showed me 1/4 fuel left. This morning I started the car and BOOM half tank again. I almost punch that gage out of this world, but indeed I didn't have any coffee.
I heard stuff from having algae in the tank, to shorts, to loose grounds or maybe even a defective sending unit. I got the unit from http://www.autopartsworld.com. is it new? rebuild? it was about 60 bucks and the MB dealer ask about 150 for it.
If anyone can help me fix this problem, it would be very much appreciated, and if you are in Sacramento CA, let me know and the beer is on me!
Thanks guys

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Old 10-24-2005, 03:39 PM
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If the temps where you are is warm enough, I would add more veggie oil since a little helped it. I also heard that running bio will loosen sticky sending units.
My jumpy guage fixed when I put in about 1/4 tank of veggie to a 3/4 tank of diesel.
If you are leary of putting more veggie in the tank, you may want to try lots of atf fluid.
Good luck.
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  #3  
Old 10-24-2005, 04:50 PM
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Update:

the fuel level needle is just below half tank, it didn't move since I started the car this morning. I drove about 25 miles or so and I know I have somewhere between R and 1/4 tank.
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Old 12-25-2005, 07:28 AM
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Do you have black specks in your prefilter if so you probably have algae which is actually bacteria. if not I suspect the gauge is faulty
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  #5  
Old 12-25-2005, 07:56 PM
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Diagnostic

Quote:
Originally Posted by baraboom
Before the forum went down I posted this thread and got one response that help a little bit.
It is about the fuel gage on my 87 300D.
I replaced the fuel sending unit about 3 weeks ago.
When I fill up the tank everything is fine until about one half tank is left.
When the tank reaches about 1/4 sometimes, only when the key is turned to the glow plug position, before starting it shows me the right amount of fuel 1/4.
Car starts and the fuel indicator needle moves very slowly toward the half tank, after about 10 minutes it shows half tank or just a little bit below that, and doesn't move.
Sometimes it moves, slowly toward the 1/4 mark again.
Stop the car after 1 hour or so of driving turn the key to the on position, it shows me half tank. Start the car, it jumps to the 1/4 mark.
Sacramento CA.
Thanks guys
First step:
You need to clean the grounds, behind the instrument cluster, battery to body, and sender to body.
Second step:
Replace every fuse in the vehicle with NEW ones.
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  #6  
Old 12-25-2005, 07:57 PM
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Quote:
Originally Posted by Tangent
Do you have black specks in your prefilter if so you probably have algae which is actually bacteria. if not I suspect the gauge is faulty

we have pressured this before ... Fungus.. not algea.. Fungus not algea
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  #7  
Old 12-25-2005, 09:01 PM
Craig
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Given that replacing the sending unit did not fix the issue, I doubt it is related to the sending unit "sticking" so I doubt adding veg. oil is going to help. My guess is the problem is at the gauge or the wiring. The gauges are very sensitive to grounding issues. I fixed a jumpy fuel gauge in my 240D by adding a new ground wire directly from the instrument cluster to a body ground. I agree, that you should check all the grounds to make sure they are making good contact.
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  #8  
Old 12-25-2005, 10:24 PM
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Quote:
Originally Posted by TheDon
we have pressured this before ... Fungus.. not algea.. Fungus not algea
I only said algae so he would not be confused,
I also said algae which is actually bacteria.
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  #9  
Old 12-25-2005, 10:45 PM
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I have a jumpy fuel guage as well. The #@!% thing wags like a dog's tail occasionally when it gets to 1/2 or less. Actually the only gauge that seems to work reliably is the temp gauge. The oil pressure gauge is the worst of the bunch because it works then it doesn't. The W124 gauges are crap compared to my W123. Stupid electronics. I've went through the grounds and they seemed fine. Changing the fuses was futile also. Helped NOTHING. Bosch was spying on Lucas when MB decided to design the 124's instruments. POS. The only thing I like is the engine in my 124. Everything else is garbage! FUI!

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