Fuel Gauge Still Not Working? - Team Camaro Tech
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post #1 of 18 (permalink) Old Aug 25th, 12, 05:43 AM Thread Starter
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Fuel Gauge Still Not Working?

Hey everyone,
I just installed and all new fuel system and my fuel gauge still does not work.

Some backround, my fuel gauge has not worked since I bought the car over 5 years ago. When I fill up the tank with gas it only reads a 1/4 tank on the fuel gauge and goes down from there as I drive. I tried troubleshooting the old sender etc and never got a good reading so figured that was it. Last year my gas tank started to leak, so I decided I was going to replace everything, tank, sender, full 1 peice SS fuel line etc.. While I had the old fuel system removed I tested the wiring in the car from what I read on here. I hooked up the resister wire in the trunk that runs to the sender top. I then grounded and ungrounded the end of that connector that connects to the sender, and the fuel gauge in the car would sweep from Full to empty each time. So I was under the assumption all the wiring in the car was good. I tried testing the old sending unit from the old tank and could not get it to read the correct ohms, so i assumed this was my problem.

I ordered all new parts. Everything is new from the tank to the mech. fuel pump. I tested the new sender when I got it and the ohms consistently read around 90 and 0, so I thought I was good to go. I just recently got everything put back in the car. Before I installed the tank, I cleaned the resister wire connections with a wire brush and I even taped the top of the wire to the sender so I knew it was a good connection and would not come off when the tank went back in.

Put gas in it the other day and took it for its first ride and the fuel gauge is doing the same thing!!!!!!! When I filled it up with gas it is only reading a 1/4 tank full just like the old tank and sender. I am not sure where to go from here. I thought the wiring was good when I tested it with everyting removed, and the new sender was good when I tested that too. I sanded down the ground spot too on the strap mount to make sure it was clean and tested it to make sure it was.

Can anyone offer any comments or opinions on what i am missing here. I am not sure what else could be wrong. thanks for all the help!

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post #2 of 18 (permalink) Old Aug 25th, 12, 06:11 AM
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Re: Fuel Gauge Still Not Working?

Sean,
You will need to run through the troubleshooter once again to isolate the issue to either the sender, ground, gauge, or wiring.

Did you test the sender after you wire brushed it? What are the ohm's readings from the sender. Are you getting a full range 0 to 90 if you manipulate the float with a wooden or bamboo stick?

69 without console gauges and low fuel warning module - center or right hand dash pod gauge?
If so check the back for the wire resistor and test to make sure it is not broken.

69 with console gauges and low fuel warning module - if original AC Delco, or Classic Head Quarters reproduction check the resistor on the rear of the fuel gauge for ohms and condition (New Classic HQ version uses a ceramic resistor pack so don't be confused if you are seeing that on either original or reproductions as they are interchangeable)

Reproduction OER gauges do not have external resistors on the fuel or temp gauges.

Let us know what you find.

If you get the full range 0-90 from the sender, and can also read that at the gauge connection, then the gauge is bad, or was reset by a previous owner (only can do this with original right hand dash gauges) or the resistor is wrong, damaged or missing, or you have a dash ground issue.


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post #3 of 18 (permalink) Old Aug 26th, 12, 05:25 AM Thread Starter
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Re: Fuel Gauge Still Not Working?

Brian, thanks for the reply.

Yes I tested the new sender several times when I got it. It consistenly read 0 to around 90-100 with my ohm meter when testing it so it seemed to be working fine. The sender is in the tank which is now in the car so I can't manually test it right now. I have probably around 12 gallons in the tank right now but the gauge is reading right under a 1/4 tank.

The car has the 4 gauge pod on the center console. So the gas gauge is on the front left of that pod. I think it might be a repo that the previous owner bought, just not sure which one. When I get some time in the next week or two I will try to take the center console apart to take a look behind the gauges. How do I test the gauge or resister? Do I remove the resistor? I am still learning most electrical troubleshooting, its definitly not a strong point!

I will check the ground on the gauge while apart as well, but I thought from reading on here that by testing the wiring from the sender connector on the trunk harness like I did while the tank was out that that would tell you if there was a wiring problem somewhere. When I tested this way the fuel gauge would sweep from empty to full each time I grounded and ungrounded the connection with my ignition key on. I thought that I read that was an indication that the wiring including the ground etc. behind the gauge was in good working order.

thanks again for all your help!

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post #4 of 18 (permalink) Old Aug 26th, 12, 05:34 AM
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Re: Fuel Gauge Still Not Working?

You can measure sender resistance on the removed tan wire from the gauge, or harness connector, to the trunk.
You can get two 50 ohm resistors, or a 0-100 ohm potentiometer, and at the sending unit connector, attach the test resistors and check gauge position.
Two resistors in series = 100 ohms = full tank,
One resistor = 50 ohms = half tank
Two resistors in parallel = 25 ohms = quarter tank.

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post #5 of 18 (permalink) Old Aug 26th, 12, 06:43 AM
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Re: Fuel Gauge Still Not Working?

And as for testing once in the tank, the sending unit may have been happy when you bench tested but now in the tank there maybe an issue. Reading Ohms as Everett describes. Use a bamboo or wooden dowel to manipulate the float and see if you are getting a live reaction in Ohm's read.

The gauge sounds fine if you get past full past empty reactions to the tests outlined in the troubleshooter. But you will need to remove the sawtooth gauge pac top cover to read the ohms off the connector, then across the resistor card if present, or the ceramic chip if in use. If it is an OER replacement gauge the resistor is built into the gauge and can not be tested.

So if you are getting a full range of Ohm's as you test the float, and for this posting lets say you are getting 50-ish Ohms from the true level of 1/2 - tank of fuel at the trunk connection and about the same at the gauge connector, and then you connect the gauge again and you get something other then 1/2 a tank you have a gauge, or resistor, or incorrectly wired Low Fuel Warning Module.

So at that point again break it down to isolate the issue. 50 ohms at the connector, test the resistor alone if it is broken you will get a zero reading since it has no full path for your probes. If it checks out to have resistance, then try the gauge with out it. If you get 1/2 tank you have internal resistance. Problem solved.

If the LFWM is incorrectly installed, or it is dead this could be your issue.
If connected correctly, disconnect it and then reconnect the gauge 1/2 tank then the module was scrambling signal. Replace the module.

If the wires are incorrectly connected, remove the unit, check the gauge reading and if correct 1/2 tank readings then install the module getting the wires on the correct posts and yellow lead connected to the harness, and bulb in the low fuel warning. If it is an original OEM module there is a light bulb socket at the top - DO NOT USE WITH A BULB IN PLACE. If once connected you go back to incorrect gauge readings the module is bad. Replace and problem solved.


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post #6 of 18 (permalink) Old Aug 29th, 12, 05:10 PM Thread Starter
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Re: Fuel Gauge Still Not Working?

Thanks guys for the replys. I am going to stop at radio Shack and see if i can pick up a few resistors to test the wiring with again.

Brian, where is the is the Low Fuel Warning Module located? This is the first I have heard of this module, so i want to try to find it to see if your above advice might work.

thanks again

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Front - 15x6 with 215/65
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post #7 of 18 (permalink) Old Aug 29th, 12, 11:22 PM
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Re: Fuel Gauge Still Not Working?

Sean
The Low Fuel Warning Light Module is a round unit with four wires similar to this reproduction - minus the light socket at the top which was only used to mount the unit.

Classic Head Quarters reproduces an almost exact OEM style with the socket clips for mounting - note that the light socket was not used other then to mount the unit in the back of the plate.


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post #8 of 18 (permalink) Old Aug 30th, 12, 09:31 AM Thread Starter
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Re: Fuel Gauge Still Not Working?

Thanks Brian for the pics. Very helpful!

I assume this is located inside the console under the gauges or is this under the dash somewhere? I'll have to take a look for this when I get time to take the console apart.

thanks again for the help

1969 Camaro - LeMans Blue
383ci Stroker ~ M22 4-speed ~ 12-Bolt Posi-3.73
AR Torq Thrust D Wheels:
Front - 15x6 with 215/65
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post #9 of 18 (permalink) Old Aug 30th, 12, 10:26 AM
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Re: Fuel Gauge Still Not Working?

Quote:
Originally Posted by SR77 View Post
Thanks Brian for the pics. Very helpful!

I assume this is located inside the console under the gauges or is this under the dash somewhere? I'll have to take a look for this when I get time to take the console apart.

thanks again for the help
Yes. Here is a picture from another post here yesterday. It looks like a quarter roll of quarters in these pictures with the exposed circuit board.

The module if original has clips on the top circling a bulb socket. The clips push into the back of the mounting plate between the fuel and the oil gauge. If it is aftermarket reproduction without clips then it just hangs under the pac.
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post #10 of 18 (permalink) Old Aug 30th, 12, 03:03 PM
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Re: Fuel Gauge Still Not Working?

Do you have a good ground on the fuel tank? Tank needs to be grounded to the Frame

That's my guess based on what you've go through so far.

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post #11 of 18 (permalink) Old Aug 31st, 12, 08:00 AM Thread Starter
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Re: Fuel Gauge Still Not Working?

Brian, thanks again for the good pics. I will take a look when I get this console apart. I am working on a battery/charing problem right now as I am not sure if my ammeter is working right either.

John, I have the sending unit grounded to the stock location at the strap mount. Was the gas tank grounded too by the factory? I don't remember reading about a sepaerate tank ground. I can run a quick test ground strap to see if that changes anything.

1969 Camaro - LeMans Blue
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AR Torq Thrust D Wheels:
Front - 15x6 with 215/65
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post #12 of 18 (permalink) Old Aug 31st, 12, 09:49 AM
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Re: Fuel Gauge Still Not Working?

Tank was not grounded, just the sending unit.
You can disconnect the LFM from the gauge and check to see if the gauge reads the level suspected in the tank.

OE ammeter is hooked on the horn relay buss bar and the battery junction block.
Turn on headlamps and ammeter should go tot he left if engine is not running.
With Vr warm after running engine for about 20 minutes at 2000 rpm, voltage across battery with no accessories on, should read about 13.8 volts.
You might be just better to replace the mechanical VR, identified by a tall cover, with an electronic VR, short cover. Better electrical system voltage closer to 13.8 volts at idle will make for a fuller charged battery.

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post #13 of 18 (permalink) Old Aug 31st, 12, 05:15 PM
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Re: Fuel Gauge Still Not Working?

Quote:
Originally Posted by Everett#2390 View Post
Tank was not grounded, just the sending unit.
The Fuel Sender itself has to be grounded (Black wire C310) C310A Tan wire runs to gauge.

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post #14 of 18 (permalink) Old Aug 31st, 12, 07:59 PM
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Re: Fuel Gauge Still Not Working?

Quote:
Originally Posted by Vega$69 View Post
The Fuel Sender itself has to be grounded (Black wire C310) C310A Tan wire runs to gauge.
Correct.

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post #15 of 18 (permalink) Old Nov 25th, 12, 04:01 PM Thread Starter
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Re: Fuel Gauge Still Not Working?

I know it been a while but I finally got around to taking things apart last month and wanted to post back in case any else has an issue. I took the console gauges apart, (repos with no low fuel module), bought some resistors from radio shack and ran all kinds of test leads. Tried the resistors, tested grounds and still was having problems with it not reading. Weird thing is gauge works when connecting and disconnecting the trunk harness. Tried all weekend playing with this and got no where. Right before I was about to put the gauges back in the console i decided to tighten the nuts on the back of the fuel gauge and voila, it finally worked. So for anyone else having issues with the fuel gauge and a resistor does not work, check the connection on the back of the gauge as well. I assume is had something to do with the resistance wire connection on mine.

1969 Camaro - LeMans Blue
383ci Stroker ~ M22 4-speed ~ 12-Bolt Posi-3.73
AR Torq Thrust D Wheels:
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