Fuel sender or guage problem? - Team Camaro Tech
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post #1 of 21 (permalink) Old Mar 13th, 11, 07:06 AM Thread Starter
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Fuel sender or guage problem?

Installed a new sender unit in the tank,when i fill the tank with gas it will go a little past the full mark,but i run out of fuel when the guage still reads 1/4 tank? I do have a sump welded in the tank and fuel lines come out of that, could this be the reason or is something wrong with sender or guage? Any help appreciated


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post #2 of 21 (permalink) Old Mar 13th, 11, 11:04 PM
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Re: Fuel sender or guage problem?

I believe the resistance of the sender should vary between 0 and 100 (90 something?). You may want to start there. Also, is it a stock gauge? Dash or console location? Some people have added resistance to make their gauges read more accurately.


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post #3 of 21 (permalink) Old Mar 14th, 11, 04:59 AM Thread Starter
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Re: Fuel sender or guage problem?

Stock guage in the dash


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post #4 of 21 (permalink) Old Mar 14th, 11, 09:31 PM
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Re: Fuel sender or guage problem?

I'd start by making sure all the connections are clean and solid. Check all grounds. The circuit board on the back of the instruments may needs some attention, too. While you are back there, measure the resistance between the tan wire and ground with the connector unplugged from the instruments. Make sure it is in a range you would like it to be based on the fuel level in the tank.


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post #5 of 21 (permalink) Old Mar 15th, 11, 06:34 PM
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Re: Fuel sender or guage problem?

I would remove the tank and then remove the sending unit. Check the resistance on the sending unit with a ohm meter. Down should be 0 ohms and up should be 90 ohms or somewhere close. That right there will tell you if the sending unit is right.

Hookup up the sending unit with the 2 required wires while you hold it in your hand. One from the wiring harness and one for ground. Turn the key on and have someone inside the car watching the guage. With the float all the way down should be empty, all the way up should be full. If that all works out then start doing some measuring to figure the relationship of the float to the inside on the tank. You might have to bend the float down so when the tank is on empty it reads right. Then check the full setting.

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post #6 of 21 (permalink) Old Mar 15th, 11, 07:15 PM Thread Starter
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Re: Fuel sender or guage problem?

Checked the sender tonight with the brown wire disconnected and key in the off position was reading 34.5 ohms, my guage is reading just a little over 1/4 tank.


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post #7 of 21 (permalink) Old Mar 15th, 11, 11:13 PM
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Re: Fuel sender or guage problem?

Hmmm. As you know, that's about 10% or more too high if there is really 1/4 tank. But it's not off by a ton. It may stink, but dropping the tank may be the best solution. Then, you can bend the float arm up a bit and remeasure the resistance. While it's out, you can test full scale readings, too. Then, calculate something closer to the 1/4 tank value and shoot for that. Or empty the tank (better when dropping it out of car anyway) and go from there...

I think I've also read of other members actually taking their gauge appart and repositioning the pointer, too? Another not so fun job...


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post #8 of 21 (permalink) Old Mar 16th, 11, 05:23 AM Thread Starter
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Re: Fuel sender or guage problem?

Quote:
Originally Posted by flyingskibiker View Post
Hmmm. As you know, that's about 10% or more too high if there is really 1/4 tank. But it's not off by a ton. It may stink, but dropping the tank may be the best solution. Then, you can bend the float arm up a bit and remeasure the resistance. While it's out, you can test full scale readings, too. Then, calculate something closer to the 1/4 tank value and shoot for that. Or empty the tank (better when dropping it out of car anyway) and go from there...

I think I've also read of other members actually taking their gauge appart and repositioning the pointer, too? Another not so fun job...
What should ohms be at 1/4 tank i thought it would be around 22.5 if 1/2 tank is 45ohms,so if im a little over 1/4 tank 34.5 ohms would sound about close????


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post #9 of 21 (permalink) Old Mar 16th, 11, 07:02 AM
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Re: Fuel sender or guage problem?

Welp, I figure out of 100, 1/4 would be 25. So, again out of 100, 34.5 - 25 = ~10 which is ~10%. But if the max resistance is more like 95 or 90, that would make 1/4 somewhere below 25. That is where I got the 10% or more from...

34.5 - 22.5 = 12
12 / 90 = .13333

That is more than 1/8 scale and 13.3% off.

It's all meaningless, actually. It is either bad wires or connections adding extra resistance or the sender needs to be adjusted...

Just thinking out loud. :-)


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post #10 of 21 (permalink) Old Mar 16th, 11, 07:47 AM
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Re: Fuel sender or guage problem?

You really need the sender out of the tank and use a ohm meter to see the full range of the sender. I mentioned this above.

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post #11 of 21 (permalink) Old Mar 16th, 11, 10:02 AM Thread Starter
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Re: Fuel sender or guage problem?

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Originally Posted by prostreet69camaro View Post
You really need the sender out of the tank and use a ohm meter to see the full range of the sender. I mentioned this above.
Will do, but if i need to bend the rod which way am i bending it down or up and how do i do know how much too bend??


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post #12 of 21 (permalink) Old Mar 16th, 11, 12:46 PM
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Re: Fuel sender or guage problem?

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Will do, but if i need to bend the rod which way am i bending it down or up and how do i do know how much too bend??

Do you have a DMV / ohm meter?

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post #13 of 21 (permalink) Old Mar 16th, 11, 01:17 PM
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Re: Fuel sender or guage problem?

A buddy of mine had an issue with a 69 dash mounted factory gauge reporting over full and over empty. We pulled the tank and I tested for him the ohms for full half and empty positions on the sender and everything was dead on. In asking around for solutions an old-timer at the local speed shop said the simple fix is to just reset the pointer. Process is to remove the screws for the bezel and expose the pointer. Then gently pull the pointer out and you will feel and hear a click and all resistance on the pointer will ease. Make sure you have a full or an empty tank to use as the set point. We used the empty tank and reset to the true empty position. Then all we had to do is gently push back in the pointer until it clicks and re-attach the bezel. Filled the tank with half and it reported half. Filled the tank, read full, over filled to the top of the filler neck, over full. Maybe yours is the same situation?


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post #14 of 21 (permalink) Old Mar 16th, 11, 02:50 PM Thread Starter
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Re: Fuel sender or guage problem?

Quote:
Originally Posted by prostreet69camaro View Post
Do you have a DMV / ohm meter?
Iam using a fluke tester that has ohm meter as well as voltage and amperage


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post #15 of 21 (permalink) Old Mar 16th, 11, 02:51 PM
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Re: Fuel sender or guage problem?

You can also take the tan wire for the sending unit and ground it. Use the one going to the guage in the trunk. If the tank is out then use the wire to the tank. Then turn the key on and see if it goes to empty.

Also if you do a search there is all kinds of info on sending units and fuel guages.

Mike
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