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Pete, Re: Ford Fuel Gauge


Mike kZ

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It really depends on what your Datsun sender reads at Full and Empty. I have three, and they all read a bit differently.

 

Taking the average of the resistance values for Empty for the senders I get about 88 ohms. The average value for full is about 8 ohms.

 

The stock Ford sender (according to Autometer) is 73 ohms Empty, and 8-12 ohms full.

 

So to use the stock Datsun sender and have the gage for the Ford fuel level to read Full when the Datsun sender is at full, and the gage to read Empty when the Datsun sender is at empty, you need to add some resistors to the circuit. Here's the circuit that will make the gage read full and empty with the Datsun sender:

 

Fuelgagecircuit.gif

 

You need to hook a 2 ohm resistor to the fuel sender output at the tank, then hook the sender wire that went to the stock gage to the Ford type gage sensor terminal (I used the Autometer Pro-Comp, PN 5416). Then hook a 380 ohm resistor to the sensor terminal and the other side of the resistor to ground. These two resistors will change the sensitivity and offset of the Ford gage to match the Full and Empty signal from the Datsun sender.

 

No telling if it will be correct between empty and full! The Ford movement appears to be more non-linear than the Datsun gage, so it may read 1/4 tank when you have 1/2 tank.

 

You might need to experiment with different values of resistors to get it to work right at E and F. If somebody wants the equations to solve for the resistors, let me know.

 

Hope that helps,

 

------------------

Pete Paraska - 73 540Z - Marathon Z Project

pparaska@home.com

Pete's V8 Datsun 240Z Pages

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Sorry, I was away on work/travel and then a (shortened) vacation.

 

The 380 ohm adjusts the "range" of the meter. The 2 ohm adjusts the "offset of the meter, mostly affecting the Full reading.

 

I tried it with one of the senders I had out of the tank and it was good with these values. I need to get my tank full to mak the final resistor selection, since I can't find the notes I made for the full and empty outputs of the new sender in the tank.

 

The problem with a variable resistor is that they wander a bit, especially the cheaper carbon based ones. A wire wound potentiometer would be better. I tend to just keep trying different resistors and combinations of parallel and series resistors to the the effective resistance that works best. I also have a resistance "decade box" that I can adjust from 1 ohm to 10Megohm with rotary switches for each decade - makes it real easy! You still have to find a resistor or parallel/series set of resistors that will actually give the resistance you need. They have a tolerance and for this type of small resistance, it can really add up and screw you.

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