Fuel sending unit - Team Camaro Tech
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post #1 of 6 (permalink) Old Nov 29th, 09, 11:13 AM Thread Starter
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Fuel sending unit

I have roughly 9 gallons of fuel in my gas tank, from the trunk connector. My ohm meter reads .01, shouldn't it read higher? I did all the testing for the guage and it works fine. I guess my question is roughly what should my ohm meter read with about 9 gallons of gas in tank???
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post #2 of 6 (permalink) Old Nov 29th, 09, 12:11 PM
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Jim
 
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Re: Fuel sending unit

I would think with 9 gallons in a tank the meter should read about 45 ohms (on an 18 gallon tank).
You should be able to figure what the meter reads by knowing what the range is of the sender (0-90 ohms) and the size of the tank.
If you have a 20 gallon tank and have 20 gallons of fuel in it the sender should read 90 ohms. If it only had 10 gallons then 45 ohms, and empty 0 ohms.
If you had a 16 gallon tank then 8 gallons in would be 45 ohms, 16 gallons 90 ohms, and empty, 0 ohms.
I would tend to think that even with 2 or 4 gallons in the tank you would want the sender to measure 0 ohms so that in your mind when you see the gauge on empty you still have some fuel to get to a gas station.

When I test 0-90 ohm GM fuel level systems I use some resistor values close to 22.5 ohms for checking the gauge to see if it reads 1/4 full tank. I then swap in a resistor close to 45 ohms to see if the gauge reads close to half full. I then tie the 45 ohm and 22.5 ohm resistors in series to give me 67.5 ohms to see if the gauge reads close to 3/4 full, and then either use two 45 ohm resistors in series or a resistor close to 90 ohms to see if the gauge reads full.

Jim

1974 Spirit Of America Nova (being restored), 1973 Nova Custom, 1968 Chevy II (Garage Find 2012)

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post #3 of 6 (permalink) Old Nov 29th, 09, 12:42 PM Thread Starter
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Re: Fuel sending unit

so the ground on the sending unit is no good, or the sending unit itself is no good right???
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post #4 of 6 (permalink) Old Nov 29th, 09, 12:49 PM
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Re: Fuel sending unit

Quote:
Originally Posted by railer3 View Post
so the ground on the sending unit is no good, or the sending unit itself is no good right???
That is correct.

Mike
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post #5 of 6 (permalink) Old Nov 29th, 09, 12:56 PM Thread Starter
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Re: Fuel sending unit

THANKS

Ron
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post #6 of 6 (permalink) Old Nov 30th, 09, 11:33 PM
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Steiner
 
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Re: Fuel sending unit

Sounds like you're testing it correctly without power on it. You're just unplugging it from the connector inside the trunk and checking from there to ground, right?

Perhaps the sender cable has just chafed through between the tank and trunk floor. Either way, it's all easy to change out and you get to find all sorts of other stuff that needs to be replaced at the same time....at least I did.

If you loosen the nuts on the tank straps all the way to the ends of the bolts, you may be able to get the tank to drop down enough so you can unplug the sending unit cable and probe right on the sending unit....if it's a '69 anyway.

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