Fuel sending unit - Team Camaro Tech
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post #1 of 11 (permalink) Old Jan 23rd, 07, 08:12 PM Thread Starter
 
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Fuel sending unit

I have searched the other posts but could not find my answer...I bought a new sending unit and before I install it I am checking the ohms. I am getting like 1 ohm with the lever down and 99 ohms with the lever in the up position. I have seen where it should be 0 for empty and 90 for full. My question is do I have a defective sending unit if it is showing 99 ohms with the arm up? Does this have to be at 90 ohms max or within an ohm or two?

Thanks...
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post #2 of 11 (permalink) Old Jan 23rd, 07, 11:12 PM
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Re: Fuel sending unit

Try a different meter and see what reading you get. I might just be your ohm meter is off.......otherwise the sending unit still should be okay.

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post #3 of 11 (permalink) Old Jan 24th, 07, 05:07 AM Thread Starter
 
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Re: Fuel sending unit

I will try a different ohm meter.

In the meantime, is there an easy way to test the guage while it is out of the car? I am thinking that if I connect the positive stud to a 12 volt source with the sending unit attached, and ground the other stud, i should be able to move the arm on the sending unit to produce the same effect as if the unit was in the car. would the sending unit be attached to the positive or ground? Or is there an easier way to test the guage out of the car?
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post #4 of 11 (permalink) Old Jan 24th, 07, 01:10 PM
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Re: Fuel sending unit

Hi! I just received my sender from C.I. and measured it 0.6 ohms @ min and 97 ohms @ full using 2 short pieces of jumper wire to connect my test leads to the terminals. I still havn't installed it yet.
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post #5 of 11 (permalink) Old Jan 24th, 07, 05:29 PM
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Re: Fuel sending unit

I have found that 9ohms wont matter on your fuel gauge. Just as long as you have more than 74ohms, because thats where the gauge will actually fall UNDER the 'F' full mark.

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post #6 of 11 (permalink) Old Jan 24th, 07, 05:53 PM
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Re: Fuel sending unit

the sender sounds fine.





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post #7 of 11 (permalink) Old Jan 24th, 07, 06:31 PM
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Re: Fuel sending unit

I agree too. The sender sounds fine.

I guess they need to add a silver or gold band on the unit to allow us to know how much tolerance it can have like 5% or 10% .

If it was reading like 30 ohms to 200 ohms or 1 ohm to 30 then there would be a problem with a 0-90 gauge.

Try this too next time you have a meter out. Touch both leads together and on the low ohm scale the meter should read 0.00 ohms. If it reads 1.2 or some other number subtract this from the number when the meter is across a resistor to get a better final figure. Old analog meters used to have a zeroing adjustment to compensate for the internal battery state and test lead resistances.
I just got a flyer from Fluke and they now have 4 wire ohm meters for very accurately checking resistances. The other two leads compensate for things.

Yep, the sender sounds good to go.

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post #8 of 11 (permalink) Old Jan 24th, 07, 06:55 PM Thread Starter
 
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Re: Fuel sending unit

What about a way to check the guage while it is out of the car? I am thinking of taking it in to a speedo shop and have them check it out, but I thought there would be or is a simple way to test the guage itself...
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post #9 of 11 (permalink) Old Jan 24th, 07, 07:17 PM
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Re: Fuel sending unit

yes, you can wire it as you described and bench test it. Are you uncertain on the guage itself?
Best way to check out the whole system would be to connect the sender without putting it in the tank. Use the normal ground wire too. Push the float up and down, gauge should move.





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post #10 of 11 (permalink) Old Jan 24th, 07, 07:53 PM Thread Starter
 
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Re: Fuel sending unit

I would like to rule out a wiring problem, so I thought the best way would be to bypass the existing wires. The rear harness has a wire that was burned down to the bare wire throughout most of the harness. Now that I have the guages out I can see that the wire that was burned up had something to do with the lights since the new wire someone put in is connected to the light switch. I would assume that there must have been a short with one of the wires for the tail lights. I checked into a new wire harness and found out that since they spliced the wires to the switch, I would need to get a new under dash harness and also the rear wire harness which together is about $520. I have never seen the guage go down past 1/2 tank even with the gas tank empty. Since I have to upgrade my fuel lines from 5/16 to 3/8 and this required a new sending unit, I thought this is the perfect time to figure out why my guage isnt reading correctly.
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post #11 of 11 (permalink) Old Jan 26th, 07, 04:01 PM
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Re: Fuel sending unit

Quote:
Originally Posted by Liveinaz View Post
What about a way to check the guage while it is out of the car? I am thinking of taking it in to a speedo shop and have them check it out, but I thought there would be or is a simple way to test the guage itself...
I use a 0-100 ohm variable potentiometer (volume control) from Radio Shack (about five bucks) to check fuel gauges. Connect the center tap to either outer tap as shown, connect the leads to a VOM (ohms scale) and mark the shaft for 0, 45, and 90 ohm positions. Then use a jumper wire from the (+) post on a battery to the "I" (ignition) terminal on the gauge, and connect the tool from the "S" (sender) terminal on the gauge to the (-) post on the battery. With the shaft at the "0" mark, the gauge should read empty; with the shaft at the 45-ohm mark, the gauge should read about half-full; with the shaft at the 90-ohm mark, the gauge should read "full".

DO NOT connect +12V to the "S" (sender) terminal on the gauge, or you'll fry the windings.




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