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Automotive Fuel Level Sending Unit

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Fluffy

New Member
This is my first time posting so I hope I put this in the right place. I'm very electronically inclined and have had some experience with rudimentary circuit design for my own projects but I am in no way an expert. I'm in the process of fixing up a 1988 Camaro and I have a question about the feasability of a 'resistance converter.'

For some context, new vehicles are very sophisticated in how the gauges operate, the needles are steady, very accurate, and rarely fail. This has not always been the case. With these old cars the gauges are notoriously inaccurate, in particular, the fuel gauges.

The gauge is fed a resistance level from the fuel gauge 'sending unit' located in the fuel tank which is basically a float that moves up and down with the volume of fuel in the tank. Since the float moves with any slosh of fuel when driving, the gauge picks up on it and as a result the fuel gauge moves erratically displaying false information.

Ford came up with a fix for this called a 'slosh module' which simply dampens and lags the resistance values from the sender to the gauge. My plan is to take one of these slosh modules from an older Ford vehicle and put it into my Camaro.

Here's my problem. The Ford fuel sending units read from a range of 16-158 Ohms (16 being empty, and 158 being full) while the older GM style sending unit reads from 0-90 Ohms. The Ford slosh module won't be compatible with my sending unit because the resistance values don't match. Is there a way I can make a circuit that will convert the Ford resistance values to that of GM? Effectively convert the signal range from 16-158 ohms to 0-90 ohms?

That way I can use the Ford slosh module with my sending unit without having to make or buy a slosh module myself.

Can anyone offer some advice here? It would be much appreciated!
 

shortbus=

Well-Known Member
Most Helpful Member
Lets see if i have this right, you want to make or adapt a Ford part that has page after page of Google hits on how to disable them in a Ford? Makes me wonder why?
 

Colin

Active Member
First you will have to fit the 0-90 ohms to the input that previously read 16 to 158 ohms because both are simply a reading of a low value to a high value.
It may depend on the resistance inside the module that makes up the other leg of the voltage divider.
We don't know the value of this resistance.
That's why you have to fit the gauge externally and provide us with: LOW HALF and FULL readings.
Then we can work out the conversion.
 

Reloadron

Well-Known Member
Most Helpful Member
I would just go with an after market fuel sending unit. Something like maybe a Dorman distributed by Summit Racing and other retailers. Also you need to give consideration as to if the unit you replace factory with has or uses a vapor return line? As to the fuel sloshing around and causing gauge bounce I have not seen that problem in decades going back to 1966. I just see the problems with changing form, fit and function as a larger problem than the one you are trying to cure. By 1988 most if not all fuel syatems had gauge dampening down pretty well.

Just My Take
Ron
 

alec_t

Well-Known Member
Most Helpful Member
Try this, which makes a 0-90 Ohm sender look like a 0-158 Ohm sender :-
FuelSenderAdapter(increase).PNG
The circuit inside the rectangle is the adapter itself. The other components, and the attached asc file, are for simulation purposes only.
V+ is the supply voltage to the gauge (if at least 5V), or the car's Accessory (i.e switched 12V) supply.
R1 and R2 could be replaced by a 50k trimpot to allow adjustment of the adapter's resistance 'amplification factor'.
This circuit does not provide any 'anti-slosh' function, but could easily be modified to do so with the addition of a resistor and capacitor.

Edit:
To make the 0-90 Ohm sender look like a 16-158 Ohm sender instead, connect a 9.1 Ohm resistor in series with the sender input to Q1 emitter.
 

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