Fuel Tank Sender - 62161352617

mwds

New Member
Messages
9
Reaction score
2
Location
Lawson, NSW
Hi All,
I am have a problem with re-wiring the sender unit. That is to say the wires inside.
One is clearly ground (BR)
One is for the gauge (BR-GE)
One is for the telltail (BR-SW)
I am using the same thickness wire (copper) - 0.09mm
I am getting a dead short between BR & BR-GE no matter where the float goes and I have checked that all the wires are running only where they are supposed to.

Any suggestion and many thanks in advance.
M
 

mwds

New Member
Messages
9
Reaction score
2
Location
Lawson, NSW
...I should say, the issues are within the sender unit itself. The wiring from the unit to the dash is very simple and barring cut or damaged wiring, the only other issues will be with the gauge itself.
 

eriknetherlands

Well-Known Member
Site Donor
Messages
710
Reaction score
268
Location
Netherlands, Eindhoven area
i have 2 thoughts
1. Did you remove the sender from the fuel tank and inspect it? Sometimes there is a lot of debris floating in the tank, rust particles etc. They also rust sometimes heavily inside, possibly creating a short where the wires are soldered on.

2. You mention the copper wire thickness (0,09mm). Am I right to conclude from it, that you replaced the wire of the sender itself, over which the float slides? If so, this wire is a very special wire. it has an exact resistance ohm / length. You may have replaced it with an incorrect wire giving an always low resistance. ( which, in my limited electrical knowledge is like a short)

Specs were previously discussed on this forum:
- (from 2002 forum, but should be equal for E9) Per the old BMWCCA Tech Tips book (circa 1976) the resistance wire on the gas gauge sender is approximately 6 ohms per inch
- low fuel reading should be 73,8 ohms, full tank 3,4 ohms. I measured a quite fresh NOS part I had a year ago, and empty it read 60,9 Ohms.
20170214_224554.jpg


2002 forum link: https://www.bmw2002faq.com/forums/topic/237622-fuel-tank-sending-unit-now-rebuilt/
 
Last edited:

mwds

New Member
Messages
9
Reaction score
2
Location
Lawson, NSW
Thanks Eric,
yes, we are talking about the sender rebuild. I have done this before about 8 years ago. I used a single strand of copper wire. In this case 0.09mm thick. I was getting the following resistance:
Full - 4.8ohm Empty - 62-64ohm
This registered fine on the gauge. It's just that I'm getting a short now. It's a very delicate job and the pickups on the float / wire connection is like crossing your legs with the rope passing between them. I'd like to keep the 'old girl' original, but a lever type setup would be less problematic. The thickness is in the ballpark (recommended 40 gauge) where as 0.09mm is closer to 39 guage. All in all, over 470mm of total length this is as close as it gets. The issue really is the dead short.

Ps... What really helps is that yours is the same colour as mine. ;)
 

JamesE30

Active Member
Messages
142
Reaction score
123
Location
Germany
Not to thread jack this but just while on the topic, I would like to dismantle my sender to have the filthy old top re zinc plated.

Is it a difficult process to disassemble without damaging anything, and is it possible to reuse the original wires?

Thanks for the help
 

mwds

New Member
Messages
9
Reaction score
2
Location
Lawson, NSW
Not to thread jack this but just while on the topic, I would like to dismantle my sender to have the filthy old top re zinc plated.

Is it a difficult process to disassemble without damaging anything, and is it possible to reuse the original wires?

Thanks for the help
Hi James. I very much doubt if you could do this without damaging the wires. That said, and basing my replacement wire on info above, I have ordered some NiCR (80/20) wire from the link below (40gauge).

I think my issue stems from using the wrong wire (correct resistance is everything). It's a very fiddly job and note carefully just how the wire runs on the float.
 

JayWltrs

Well-Known Member
Site Donor
Messages
706
Reaction score
356
Location
Oklahoma City
Hi James. I very much doubt if you could do this without damaging the wires. That said, and basing my replacement wire on info above, I have ordered some NiCR (80/20) wire from the link below (40gauge).

I think my issue stems from using the wrong wire (correct resistance is everything). It's a very fiddly job and note carefully just how the wire runs on the float.
I think @Tony.dreamer has done a few that work perfectly and also had them re-finished, b/c he's awesome like that. I'm not awesome like that, and tried a number of different types & gauges of wire, but the 38g-40g were the only ones that were even close. The internal terminals flex enough that it can affect the length & => resistance. My numbers:

40g Ni80 = 95-100 (e) 5-7 (f)
38g Ni80 = 58-60 2.5-4

40g KA-1 = 125-127 8-14
38g KA-1 = 78-79 4.5-4.9

40g SS 316L = 65-67 5.5-6.5 (I got 74 at the wire but could never get the SS consistent at the terminal to wire where I got closer with others)

Other things I learned; some the hard way:
--when you think you have everything clean, clean some more
--use the lightest duty soldering iron you can--25W was too much for my clumsy hands & the internal connections are super delicate
--if you doubt your skills at all, use desoldering braids to remove the old solder--the internal connections are super delicate
--"note carefully just how the wire runs on the float" Amen. Check and recheck the floating terminals & lacing through the bottom--if you kink a wire at all, start over
--different brands of wire give you different results--wire is cheap b/c it's used in vaping, & like most cheap stuff ...
-- I had a 3-5 ohm difference w the 3 ohm meters I used, and whether I used clips or probes at the top terminals-- micro-clips more consistent, but only use flat ones on the internal connections to get good contact. Also using other parts of the sender top as ground helped check readings--I had trouble getting consistent grounds.
-- The flex and bend in the internal terminals can affect the resistance more than I thought--the internal connections are super delicate .
-- Female spade connectors required cleaning further back into the wire than I thought.
-- Flat wire is easier to manage in some respects, but it seemed easier to kink and hard to keep consistently straight for the float terminals
-- arts & crafts stores have small tools for beading etc & cost a fraction of identical-looking tools sold for electronics, etc.

In the end, mine worked, but the gauge was a bit jumpier than I wanted, b/c I'm not good at small, fiddly stuff. So, I have it as a spare & bought a new one through Paul W at Max, and it works perfectly--only very small difference in the markings from original -- can't remember difference, maybe Chech instead of Germany stamp? Look under "instruments" and not "fuel tank" at W&N & Real OEM to find number.
 

mwds

New Member
Messages
9
Reaction score
2
Location
Lawson, NSW
Thanks jay,
I'm waiting with bated breath for the NiCR wire to arrive. It's a shame there isn't a lever type retro on this. All for keeping it std but here it would matter.
 

JayWltrs

Well-Known Member
Site Donor
Messages
706
Reaction score
356
Location
Oklahoma City
Thanks jay,
I'm waiting with bated breath for the NiCR wire to arrive. It's a shame there isn't a lever type retro on this. All for keeping it std but here it would matter.
When I did this in January, a few OE in Europe popped up. They were much more expensive, even before shipping, than the later Czech-marked one I bought, which was still spendy but cheaper than Paul & I expected.
 
Top