Author Topic: 280S fuel sender unit before and after fuel tank removal  (Read 469 times)

Wessel Badenhorst

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280S fuel sender unit before and after fuel tank removal
« on: 21 January 2019, 05:00 AM »
Gents

My Fuel gauge was working fine prior to cleaning out my fuel tank.

I also dismantled and cleaned out rust out of the sender unit. I refitted it and connected the wires going to the gauge as I found them.

Now my gauge is jumping back and forth erratically.

Question 1: When refitting the fuel sender must one emerse it in fuel first?

Question 2: What could be the problem here is it connections between sender and gauge or internals of the sender unit?

Thanks.
1979 280S Silver Green Metallic
1991 500SE Astral Silver Metallic

stillmatic

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Re: 280S fuel sender unit before and after fuel tank removal
« Reply #1 on: 21 January 2019, 09:26 AM »
Question 1: When refitting the fuel sender must one emerse it in fuel first?

This is not necessary to my knowledge but someone else can chip in. It can be cleaned with diesel fuel though.

Question 2: What could be the problem here is it connections between sender and gauge or internals of the sender unit?
 
If you dismantled the sending unit, chances are you have an issue with the wiring plugs, either corrosion or bad contacts. Try to remove it again and tip it upside-down a couple of times to see if the float is moving properly and if it's hitting the contacts as it goes up and down. The wiring inside the fuel unit is very delicate and prone to breaking if you don't handle it with care, if you take it apart you risk damaging it.

There's an on-demand video from mercedessource site here going into details on how to restore fuel sending units if you want to part with 12 bucks:

https://mercedessource.com/store/1970s-and-1980s-fuel-tank-gauge-sending-unit-removal-and-repair-demand-video

If you already took it out though and you get how it works, I would recommend you start by taking it out again and analysing the wiring + contacts.
Michael

1978 280SE Euro Astral Silver/Blue MB Tex
1970 250C W114

Wessel Badenhorst

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Re: 280S fuel sender unit before and after fuel tank removal
« Reply #2 on: 22 January 2019, 04:24 AM »
thanks Michael
1979 280S Silver Green Metallic
1991 500SE Astral Silver Metallic

stillmatic

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Re: 280S fuel sender unit before and after fuel tank removal
« Reply #3 on: 22 January 2019, 08:36 AM »
No worries, let us know how it went!
Michael

1978 280SE Euro Astral Silver/Blue MB Tex
1970 250C W114

Justin280s

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Re: 280S fuel sender unit before and after fuel tank removal
« Reply #4 on: 22 January 2019, 05:07 PM »
I had to take mine out 3times to get it to work.   On the last removal I wiped the thin wires with p2000 sand paper.  And removes the instrument cluster and clean  the multi plug contacts.  It now works fine.. I think it was the cluster connections were the issue..

Wessel Badenhorst

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Re: 280S fuel sender unit before and after fuel tank removal
« Reply #5 on: 28 January 2019, 12:45 AM »
No worries, let us know how it went!
My woes continue, my cables arent in a sealed connector there are three loose connectors - brown wire, black and blue and green and blue.

I had a picture of which went were - L/G/W are the three options on the sender but now I cant find my picture.

I assume brown is L/live like with houeshold electrical wires.

If I put the brown anywhere but on the L connector the guage shows full which is incorrect.

Currently I have brown on L, black and blue on W and green and blue on G.

Not sure if this is correct, the guage has at least stopped jumping around, if you turn ignition on the needle lifts a bit, the car is farily empty so it makes sense. Will go put some fuel and see if it lifts further.

Can anyone maybe confirm if I have the wires in the right place?

thanks.

1979 280S Silver Green Metallic
1991 500SE Astral Silver Metallic

rumb

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Re: 280S fuel sender unit before and after fuel tank removal
« Reply #6 on: 28 January 2019, 07:43 AM »
Brown is always ground.
'68 250S, '77 6.9 euro, '91 300SE, '98 SL500 '14 CLS550

Wessel Badenhorst

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Re: 280S fuel sender unit before and after fuel tank removal
« Reply #7 on: 05 February 2019, 11:01 PM »
My guage is sitting ate a constant 3/4 full.

Will have to pull out the sender again.
1979 280S Silver Green Metallic
1991 500SE Astral Silver Metallic

stillmatic

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Re: 280S fuel sender unit before and after fuel tank removal
« Reply #8 on: 06 February 2019, 05:07 AM »
You can try testing the sender while it's out, try turning it upside down to hear if the floater moves and if the needle oscillates.
Michael

1978 280SE Euro Astral Silver/Blue MB Tex
1970 250C W114