Help! C3 Fuel Gauge Woes. . .

[Bolisk]

I'm mentioned this in the past, got some advise, and then never tackled the problem. I'm planning on trying to fix my issue this weekend, and I now have some more details to provide to the experts here. Any feedback would be greatly appreciated.

Here is the problem I'm witnessing with my new rebuilt fuel gauge. When the tank is full, the gauge reads 1/4 full. When the tank is empty, the gauge reads empty. So the entire operation of the gauge is compressed into one quarter of the gauges capability. Note, that the gauge reads accurately within that 1/4 space. A 1/8th reading is exactly 1/2 tank. I did NOT have this problem with my old incorrect fuel gauge with the same new sending unit.

Before you provide feedback, please read the background below, as it may contain valuable information.


Background:
When I bought my car, the fuel gauge worked and read perfectly. Only problem was the gauge was wrong for the year. It had white printings and not the correct green printings. It also had the light blue color behind the dial, as opposed to that aqua-marine color for the 1970 year. The next issue was the sending unit was leaking. . .so it had to be replaced. Not wanting to change too much at once, I decided to change the sending unit first. I did this, and was able to verify that the existing gauge still read correctly. I kept it this way for a year after changing the sending unit.

After that year, I finally got around to restoring my gauges, and ordered a rebuilt correct fuel gauge from the local corvette restoration shop.

First potential cause: I suppose the new rebuilt gauge could be bad. . .

Second potential cause: When I removed the existing incorrect gauge, I kept the resistor that was on the back of that gauge, and re-used it with the new rebuilt gauge.

I have since been told that some rebuilt gauges do not need the resistor. . .or the resistor is not compatible with this correct gauge.

Thanks for your feedback!
-Jon
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[LLC5]

From your post it sounds like the resistor could be the problem, but if I were you I would contact the business that rebuilt the gauge and ask them if it should be there or not, as they would be the only people who would know for sure, they could also advise you on the correct sending unit for that gauge. If the resistor is supposed to be there after the rebuild then you could damage the gauge by removing it, again only the rebuilder knows for sure how they refurbished it. Make sure you have a good solid ground source to the sending unit also.

 

[bagger]

I replaced the entire instrument cluster in my 68 a few years back with new gauges. When I re-installed them the gas and the temp gauges were way off like yours. I took them out and replaced them and they still were screwy. Long story short, I put the resistor back on them. That was the problem. The new gauges were built with the resistor in them and the external resistor wasn't needed. Tore my dash apart for a third time and removed them. The gauges worked like they should. If you still have the external resistor on them, I'd take it off. Hope this helps you out.

 

[Bolisk]

Ok, good info. That at least proves that theory. The only concern i have is that my gauges are not "new" they are reconditioned origionals. So I'm not sure if the same applies. Maybe.

 

[6880 Mike]

I read that if you put six volts across the back of the fuel gauge, it should read half full.