Fuel gauge with wrong ohm sender

Rulebreaker · Oct 18, 2013

My truck runs on propane and i was wanting to hook up the stock fuel gauge but they no longer make the Ford 15-150 ohm sending unit they only have the GM 0-90 ohm sending unit or you can buy the sending unit and gauge together. What would happen if i bought the GM sender and hooked it up to my stock gauge? Would it read about 1/2 full when full but then go down to empty like normal? My thought was to give it a try and if it did not work then buy the gauge to go with it. I really only need to know when I'm getting close to empty I dont care if it reads full. RB

RonD · Oct 18, 2013

If you added a 15ohm resistor to the sending unit wire it will read 15 ohms when empty instead of 0 ohms, and 105 ohms when full.

So empty would be correct for '89 and up Ford Fuel gauge
105 ohms would show about 2/3s full on Ford Gauge.

Rulebreaker · Oct 19, 2013

RonD said:
If you added a 15ohm resistor to the sending unit wire it will read 15 ohms when empty instead of 0 ohms, and 105 ohms when full.

So empty would be correct for '89 and up Ford Fuel gauge
105 ohms would show about 2/3s full on Ford Gauge.

Thats a good idea, I'm guessing I can get one from Radio shack? Thanks RB

RonD · Oct 19, 2013

I would use a 20watt 15 OHM resistor, radio shack may have it but you may have to source it on-line.

14volts(engine running) at 15 ohms will max out at 13 watts

kimcrwbr1 · Oct 19, 2013

I`m just wondering how that would work? The lower the resistance the higher the guage will register. If you want to read empty wouldnt you need to have 150 ohms at the sender. Maybe get a 60 ohm resistor to give you 150 ohms empty and 60 ohms full. Just a thought.

RonD · Oct 19, 2013

kimcrwbr1 said:
I`m just wondering how that would work? The lower the resistance the higher the guage will register. If you want to read empty wouldn't you need to have 150 ohms at the sender. Maybe get a 60 ohm resistor to give you 150 ohms empty and 60 ohms full. Just a thought.

Pre-'89 Ford gauges did read that way, 73(empty)-10(full) Ohms, from what I understood he has a '93

'89 and up gauges use 16(empty) - 158(full) Ohms

Pre-'89 gauge couldn't be used at all with the GM 0-90 Ohms sender, well I guess you could build a circuit board to reverse ohms at the gauge but unless it was a vintage collectable vehicle just swapping the gauge would make more sense.

Rulebreaker · Oct 21, 2013

http://www.amazon.com/Amico-Watt-Wirewound-Cement-Resistors/dp/B0087ZDBW4

This work?

Rulebreaker · Oct 21, 2013

http://www.amazon.com/Amico-Watt-Wirewound-Cement-Resistors/dp/B0087ZDBW4

This work?

RonD · Oct 21, 2013

Yes, that should show 15 ohms at gauge when GM sender is at 0 ohms

sheltonfilms · Oct 28, 2013

RonD said:
I would use a 20watt 15 OHM resistor, radio shack may have it but you may have to source it on-line.

14volts(engine running) at 15 ohms will max out at 13 watts

Yeah but the voltage is usually supplied by the ECU's internal 5V regulator with a pull up resistor built in (I've seen them as low as 600 ohms to 1 or 2k). So the fuel sending unit is only having milliamps of current flowing through it.

Which truck is this on?

Rulebreaker · Oct 28, 2013

sheltonfilms said:
Yeah but the voltage is usually supplied by the ECU's internal 5V regulator with a pull up resistor built in (I've seen them as low as 600 ohms to 1 or 2k). So the fuel sending unit is only having milliamps of current flowing through it.

Which truck is this on?

99 Ranger

RonD · Oct 29, 2013

sheltonfilms said:
Yeah but the voltage is usually supplied by the ECU's internal 5V regulator with a pull up resistor built in (I've seen them as low as 600 ohms to 1 or 2k). So the fuel sending unit is only having milliamps of current flowing through it.

Which truck is this on?

Yes, fuel gauge systems often uses a 5v or 5v pulse system.
This doesn't change the required resistance needed for this adaptation for the 0-90ohm GM sender.
i.e. a 20watt or 2 watt 15ohm resistor would work the same on a 5v system, a 20watt would be safer to use since 14v is the highest voltage the system is ever likely to see, baring lightning strikes

sheltonfilms · Oct 29, 2013

Rulebreaker said:
99 Ranger

You change the fuel tank? The 98-up Rangers are 22-148 Ohms, earlier ones were 15-165.

Dorman makes ford sending units. Cost about 70-80 bucks.

Fuel gauge with wrong ohm sender

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