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1978 450SL--117K
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1,374 Posts
Discussion Starter #1
Below is a pic of my 450SL's fuel gage as the red light has come on. It took 17 gallons to fill it at this point. When I had the dash out, I re did the cluster--fixed the speedo, cleaned the hell out of everything and I made the secondary ground connection from the gage to the steel supports that the dash bolts to. I used the (now) miscellaneous bolt that was used for the becker radio bracket to the left of the center vents. I double checked the ground with a DMM. SO, one can see that my needle is still quite a way from the reserve indicator mark. Is this correct? because it isn't that way on the 560. So, could my gage be off? Could the float in the tank be fuxed? can I reset the needle?
 

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Outstanding Contributor
450slc5.0cab 280sl5sp 280se4.5 500se+500slAMG +250seStkW108 350sl4spdX3 500secEuro
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22,546 Posts
Perhaps this has nothing to do with the answer to your question, but someone posted their very reliable results of their fuel gauge based on lots of fill-ups at various points on the gauge.

I will search for the thread when I get some time. GleukAuf ? MBGraham? I can't remember who it was. It looked like some research worthy of the EGv107 though. Maybe it is even in there.
 

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W221 & Audio Moderator
2013 S550
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10,978 Posts
The fuel gauge "rating" post is here - http://www.benzworld.org/forums/r-c107-sl-slc-class/1570935-rating-fuel-gauge.html#post4583857

Some of the factors that throw a fuel gauge off are 1) a bad sending unit; there is a repair thread at http://www.benzworld.org/forums/r-c107-sl-slc-class/1385559-fuel-sender-repair.html but I found it inexpensive enough just to replace mine (plus I damaged my old one when I disassembled it after replacing :eek:). 2) A bad gauge. There are resistance tests for the gauge and for the sending unit at Model 107 (listed in the EGv107).

I also found that running Techron fuel system cleaner through the tank several times helped the old sending unit somewhat, before I replaced it - but it never got back to fully accurate.
 

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1978 450SL--117K
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1,374 Posts
Discussion Starter #4
Thanks guys for the input. It is very stable now with the added ground--no flakiness. Since a new gage is out (can't be made anymore?) then I should look into the sending unit.
 
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