Dead fuel gage - PeachParts Mercedes-Benz Forum

#1 04-07-2003, 11:50 AM

My '82 CD's fuel gage is totally dead. Would replacing the fuel gage sending unit located on the top of the fuel tank be a logical first choice?

#2 04-07-2003, 12:27 PM

The fuel gauge was dead when I bought my 1979 300CD, and I dumped some diesel purge into the tank, and that fixed the problem. You might want to try this, and if it doesn't work after a few tanks it might be the sending unit. You might just need to pull it out and clean it up, and if that doesn't work then you might have a bad sending unit. You might also have a bad ground connection for the gauge, which is causing it to not work.

rivermasternc · #3 04-07-2003, 12:51 PM

I just removed my fuel sending unit last weekend, cleaned it up, and replaced it. Working like a charm now.

The float had about 1/4" sludge on top of it causing a really slow response when refilled. The bottom had about 3/8" of sludge in it, causing the reserve contacts on the bottom of the float to not touch the concact points at the bottom.

The sending unit is removed with a 46mm or 1-13/16 socket. The assembly comes apart from a nut on the bottom. The resistor wires are very fine. Be careful not to break them if you try the cleaning route.

lrg · #4 04-07-2003, 09:25 PM

Before you mess with the sending unit double check to see if the circuit from the sending unit to the gauge is good. There are two wires on the top of the tank where the sending unit is located. Shorting (grounding) one wire should cause the reserve light to go on, grounding the other should pin your fuel gauge (I believe on full). If that is not happening then start checking the circuit for problems. If you do get the reserve light and gauge to work by grounding then it is probably the sending unit that's bad.

#5 04-08-2003, 09:59 AM

Thanks for all your suggestions.......I'll post my results following my weekend repair efforts.

One more bit of info....in addition to the dead fuel gage the clock is dead and so is the tach. I saw a post on replacing the capasitors on the clock, I plan on doing that. I imagine the tach is related to the cable. Speedo works.

I tend to discount any electrical grounding issues since the temp. gage functions properly. So too does the oil pressure gage but I realize that works directly off of an oil line to the gage.

rivermasternc · #6 04-08-2003, 10:30 AM

These two problems are most likely not related. The clock problem is probably related to the capacitors, the tach to the TDC amplifier (trash can on top of the left front wheel well in engine compartment). Here's all you need to know to handle the clock issue:

http://business.baylor.edu/Richard_Easley//autofaqs/clock.htm

#7 04-08-2003, 11:48 AM

Thank You very much. You wouldn't happen to have a photo of the TDC Amplifier would you? The tach used to function sporadically.....might work one day then not the next. Is this a symptom associated with the amplifier?

rivermasternc · #8 04-08-2003, 12:01 PM

Mine does the same thing. I currently have the amp on my work bench at home. Let me see if I have a pic. I'll reply again after lunch, or probably just edit this post.

-Scott

Here you go:

#9 04-08-2003, 12:58 PM

Once again, thanks to all.....this forum is amazing.

rivermasternc · #10 04-08-2003, 01:38 PM

Zat:

Here's a thread in this forum regarding the Tach Amp:

http://www.peachparts.com/shopforum/showthread.php?threadid=6051&highlight=TDC+amplifier

I believe the original poster for that thread was a 300CD 1982 also, but the problem covers several models and years.

Best of luck.

-Scott

BoostnBenz · #11 04-08-2003, 10:53 PM

Wow, it is nice that my mysterious tachometer problem will be solved. Thanks for the info, I'll try that out tomorrow, sounds like that is it. I actually added another wire to the back of my cluster today so I know it is grounded real well. I also have a twitching fuel gauge, gets a lot worse under a half tank, but still twitches somewhat over. I'm hoping my Redline DFC and enough fresh diesel will help clean the float off.