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  #1  
Old 05-22-2007, 12:07 AM
KAdams4458's Avatar
Mmm! Diesel!
 
Join Date: Apr 2007
Location: Snohomish, WA
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Fuel Sender Nichrome wire

After much fussing, I've not only managed to measure the diameter of the junk wire from the fuel sender of my 300D, I've also measured the resistance per foot.

Diameter: 0.0045 Inches

Resistance/Ft: 29.5 Ohms.

Can anyone else verify this, or am I in relatively unexplored territory?

I'm thinking I can use wire with a slightly lower resistance per foot, because I could easily adjust resistance higher with a series or series-parallel resistor circuit.

I can't be the only one crazy enough to try this.
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'77 300D Euro Delivery
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404 Milanbraun Metallic / 134 Dattel MB-Tex

Current status:
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  #2  
Old 05-22-2007, 12:42 AM
pawoSD's Avatar
Dieselsüchtiger
 
Join Date: Oct 2004
Location: Grand Rapids, MI
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Quote:
Originally Posted by KAdams4458 View Post
After much fussing, I've not only managed to measure the diameter of the junk wire from the fuel sender of my 300D, I've also measured the resistance per foot.

Diameter: 0.0045 Inches

Resistance/Ft: 29.5 Ohms.

Can anyone else verify this, or am I in relatively unexplored territory?

I'm thinking I can use wire with a slightly lower resistance per foot, because I could easily adjust resistance higher with a series or series-parallel resistor circuit.

I can't be the only one crazy enough to try this.

You may not be the only one crazy enough to try it, but you are likely the first! My sender doesn't work very well either....I just have been too lazy to remove it. I just go by miles per fill-up. Every 350-400 miles I fill up.
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  #3  
Old 05-22-2007, 01:07 AM
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Join Date: May 2004
Location: Flowood Mississippi
Posts: 438
Wire

Will throw the total range reading off some.... but any port in a storm.....depending on how much difference the new wire is per foot....Could put in an external trim pot instead of fixed resistance to loosely calibrate...best bet would be to get the right wire....but still fun things to do with fuel quantity measurement....give it a go .....post back with results....cheers!
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1980 Blue 240D (The Iron Toad)
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Last edited by yellit; 05-22-2007 at 03:15 AM. Reason: missing info
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  #4  
Old 05-22-2007, 01:32 AM
KAdams4458's Avatar
Mmm! Diesel!
 
Join Date: Apr 2007
Location: Snohomish, WA
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Well, my concern is that the wire may be a bit stretched, and thus may have different specs than it should. My best bet, as near as I can tell, will be to stick to a 29 - 29.5 ohm per foot wire. It should get me close enough. Fuel gauges aren't exactly meant to be precise.

The original wire is about a 37 AWG, but as long as resistance stays as close to original as possible, diameter won't matter too much.

I'll keep you all posted.
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- K.C.Adams

'77 300D Euro Delivery
OM617 turbo / 4-speed swap
404 Milanbraun Metallic / 134 Dattel MB-Tex

Current status:
* Undergoing body work


My '77 300D progress thread

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  #5  
Old 05-22-2007, 03:14 AM
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Join Date: May 2004
Location: Flowood Mississippi
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Wire...

I may have missed the original problem....Is the wire broken...?
I have a sender out of the car...... I could measure the ohms for you ...from a 1978 300D..
I have rebuilt 3 or 4 of these things....mainly just cleaning and removing the corrosion from the bottom attachment points around the low fuel level float contacts....All of these old senders seem to gunk up pretty quick down here in the South........
Just have to be careful if you remove the wire....it is very difficult to handle without kinking...the floats little copper slider arms are delicate also.....good idea to replace the rubber o-ring that seals the unit to the tank....kb
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1978 Yellow 300D (The Mustard Toad)
1980 Blue 240D (The Iron Toad)
1989 Grey Mitsu.4WD Mighty Max Pickup (Needs a Diesel transplant bad)

(Open the pod bay doors HAL)
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  #6  
Old 05-22-2007, 03:33 AM
KAdams4458's Avatar
Mmm! Diesel!
 
Join Date: Apr 2007
Location: Snohomish, WA
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Quote:
Originally Posted by yellit View Post
I may have missed the original problem....Is the wire broken...?
I have a sender out of the car...... I could measure the ohms for you ...from a 1978 300D..
I have rebuilt 3 or 4 of these things....mainly just cleaning and removing the corrosion from the bottom attachment points around the low fuel level float contacts....All of these old senders seem to gunk up pretty quick down here in the South........
Just have to be careful if you remove the wire....it is very difficult to handle without kinking...the floats little copper slider arms are delicate also.....good idea to replace the rubber o-ring that seals the unit to the tank....kb
Oh, yeah. It's broken.

I soldered one connection back together, but had intermittent conductivity issues, so I shook it to try cleaning the contacts. I guess I shook it a little too hard, because every connection failed in the process except for the one I soldered back together. I ended up with a number of kinks in the wire.

I do have a new o-ring on hand. Good thing, since the original practically fell apart. That's a common theme so far with this car. If it's rubber, it falls apart. If it's plastic, it falls apart. Heck, if it's metal, it falls apart!
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- K.C.Adams

'77 300D Euro Delivery
OM617 turbo / 4-speed swap
404 Milanbraun Metallic / 134 Dattel MB-Tex

Current status:
* Undergoing body work


My '77 300D progress thread

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  #7  
Old 05-22-2007, 07:52 AM
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Join Date: Jun 2006
Location: NY
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You would be better to go with a wire that is a little HIGHER in resistance rather than one that is a little low. With a higher resistance, you can shunt your sender with a resistor for calibrating Reserve withour messing up Full.
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  #8  
Old 05-22-2007, 09:24 PM
Palangi's Avatar
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Why not just get a fuel sending unit from someone parting out a 123?
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