Fuel Sending Unit Ohms

VetteDude

Newbie
Joined
Aug 21, 2019
Messages
6
Folks,
Does anyone know the ohms range for the sending units on our cars? Putting in a Holley dash in the track car and want to wire the sending unit in so I can see fuel on the dash but there does not seem to be any info online that reliably show the range. Thanks in advance!
 

NZ00Z3

Zorg Guru (III)
Supporter
New Zealand Zeds
Joined
Dec 9, 2014
Messages
909
Location
Timaru, New Zealand
Model of Z
3.0L, 2.0L Z3 Roadsters
Fuel Sender card.JPG


The above is a picture of a good used Fuel Sender Card. There are only two connections to the card and they are both swipe arm connections.

The inner swipe has no resistance, its just a common connection.

The outer swipe is resistive. By memory, the left end is a full tank and the right end is an empty tank. It is not a linear relationship due to the shape of the Z3 fuel tank.

- Full = 500 Ohms
- 3/4 = 300 Ohms approx.
- 1/2 = 85 Ohms approx.
- 1/4 = 50 Ohms approx.
- Empty = 20 Ohms

The above resistances where measured from the inner swipe to the outer swipe.
 

VetteDude

Newbie
Joined
Aug 21, 2019
Messages
6
Perfect thanks. I ohmd out the end points this evening and it came out to 500 but when I talked to Holly they thought I was nuts. Thanks for confirming.
 

Pingu

Zorg Guru (III)
3rd Party Trader
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Dec 8, 2011
Messages
1,114
I assume that your gauge has three wires (12v, earth and sensor). There may also be a wire for a light.

If so, it's easy enough to match the full scale deflection of the sender to your gauge by using a variable resistor. Then replace the variable resistor with a fixed value resistor.

The OEM sender wires both go to the instrument cluster. You will need to wire the sender so one wire goes to the gauge's sensor terminal and the other goes to earth. The resistor bridges these two wires.

You can go straight for a known resistor if you know the resistance at FSD of your gauge.

I have a non-OEM gauge (FSD = approx 180ohms) and I'm using a 300ohm parallel resistor, but yours will need to be matched to your gauge.


For parallel resistors...

1/(total resistance) = (1/resistor 1) + (1/resistor 2) + ...

1/180 = 1/500 + 1/R

1/R = 1/180 - 1/500

R = 281.25 - I'm using 300 as it's close enough.
 
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