# 1974 GTO Fuel Sending Unit Replacement



## Red74Goat (Jul 31, 2015)

*1974 GTO Fuel Sending Unit Repair*

Fuel gauge stuck at full, even when tank is empty. Did diagnostics to find out if it was the gauge or the fuel sending unit using ohmmeter. Seems to be the sending unit. 

I can't find a replacement fuel sending unit for it. Seems there are fuel sending units available for X-body GM fuel tanks through 1972, but can't find one for 1974. Any suggestions on where to find one would be welcome. I don't want to replace the entire gas tank, want to keep as much original and oem as possible.

Thanks


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## Goat Roper (Oct 28, 2014)

Call CARiD they have them listed for LeMans, you may want to pull yours out to compare.

1974 Pontiac LeMans Replacement Fuel System Parts - CARiD.com

If they don't have it they may be able to tell you who does.


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## Red74Goat (Jul 31, 2015)

Goat Roper said:


> Call CARiD they have them listed for LeMans, you may want to pull yours out to compare.
> 
> 1974 Pontiac LeMans Replacement Fuel System Parts - CARiD.com
> 
> If they don't have it they may be able to tell you who does.


Thanks Goat Roper, I'll check them out and see if I can get a lead from them.


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## Red74Goat (Jul 31, 2015)

Red74Goat said:


> Thanks Goat Roper, I'll check them out and see if I can get a lead from them.


I checked with them and unfortunately they don't carry the part. Only suggested checking e-bay and amazon (which I have done for months).

I may have found the fuel sending unit at Auto City Classic. 

I will check them out and see if they have one available.


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## BRasi (Aug 20, 2015)

I would compare to a 74 Nova to see if they interchanged.


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## 05GTO (Oct 6, 2004)

Here is a website that offers one for 1972 (FG104C) and another for 1976 (FG103C), Give them a call and see which is the correct to use for 1974,


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## Red74Goat (Jul 31, 2015)

05GTO said:


> Here is a website that offers one for 1972 (FG104C) and another for 1976 (FG103C), Give them a call and see which is the correct to use for 1974,


BRasi and 05GTO thanks for the suggestions. I checked out a vette forum where there were multiple problems with sending units and there was some success with adding Techron to the tank to remediate sulfur deposits on the sending unit. I added full tank of gas and added Techron, drove around, gauge working now. It had been registering completely full, even with only a couple of gallons of gas in the tank. Not sure if this will last, but sure beats dropping tank and removing sending unit for now! May have been problems with old gas left in tank initially causing the problems with the fuel sending unit.

Thanks.


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## 68GTO4004Spd (Jun 19, 2008)

Have you checked to see if the sending unit ground wire is connected? That will cause the gage to read full.


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## Red74Goat (Jul 31, 2015)

68GTO4004Spd said:


> Have you checked to see if the sending unit ground wire is connected? That will cause the gage to read full.


68GTO I did check the ground wire and it is/was connected. Thanks.


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## Red74Goat (Jul 31, 2015)

Bought a fuel sending unit for a 1974 Nova about a year ago, didn't have a chance to drop the gas tank until a few days ago. Unfortunately the Chevy replacement part only has a single fuel line coming out of it, but my Pontiac unit has two lines: one for the fuel and one for the fuel vapor return hose from the fuel pump back to the tank. The fuel vapor return hose connects to the fuel pump, so not having a fuel return line on the Chevy replacement part I bought would have started me down a whole different trail of mods, which I don't have any interest in doing at this time. So I decided to pull the original sending unit, disassemble it, and clean the rheostat contacts to see if that would fix it. 

My unit is a 0-90 ohm unit, with 0 ohms for empty and 90 ohms for full. I reassembled the sending unit rheostat this evening and checked it out of the car with an ohmmeter across the full movement of the float, from empty to full, and it has a 90 ohm variance. Next I will check it by connecting it to the fuel gauge in the car before installing it back into the tank and reinstalling the tank. 

I'll post few pics of the unit from my GTO in the following post.


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## Red74Goat (Jul 31, 2015)

Pic of the two lines into the sending unit. Notice the two different diameters of the lines.


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## Red74Goat (Jul 31, 2015)

Pic showing the half circle arc of the resistive element of the rheostat with the windings visible.


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## Red74Goat (Jul 31, 2015)

Pic showing the wiper (sliding contact) of the rheostat.


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## Red74Goat (Jul 31, 2015)

Pic of the rheostat reassembled after being cleaned. Also shows the float for the rheostat and the sock on the end of the fuel line.


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## Red74Goat (Jul 31, 2015)

Got the fuel sending unit rebuild completed, installed back into the gas tank, and the tank installed back into the car. The fuel sending unit seems to be working perfectly! Had a chance to replace the segments of rubber hose for the fuel line, the return line, and the vent line that connect to the tank when everything was removed. Also had a chance to get gas tank straps, area under the tank, and diff cover painted while the tank was out.


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## PontiacJim (Dec 29, 2012)

Great posting with the pics and what you did to get everything working again. Hopefully good for another 40 plus years of ownership! :thumbsup:


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## Red74Goat (Jul 31, 2015)

Thanks Jim! I hope it helps someone facing the same problem, seems like a lot of views on the topic.


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## Red74Goat (Jul 31, 2015)

When cleaning the rheostat on the fuel sending unit, I used a lint free wipe with a few drops of carb cleaner on it to clean the varnish from old gasoline off of the windings. I followed that with a wiping of the surface with some isopropyl alcohol.


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