Frank Carbone Posted September 17, 2004 Report Share Posted September 17, 2004 Hi all I had to replace the fuel tank a little while ago and I got a used one put in with the sending unit that was in the original tank installed. The problem that has sprung up is that the gas guage now reads 3/4 full when the tank is full. If I put the car into diagnostics when it's running and I'm driving the gas guage goes to full then back to 3/4 and then back to full. If I exit the diagnostics when the guage reads full it stays there but as soon as I restart the car it goes back to 3/4. My question is does the fuel gage have to be recalibrated somehow or is it on it's way out. Thanks for any help Frank Link to comment Share on other sites More sharing options...
Regis Posted September 17, 2004 Report Share Posted September 17, 2004 That's a really good question and I would certainly like to know. I'll bump this back up to the front page and hope someone knowledgeable can answer this one. "Burns" rubber " I've never considered myself to be all that conservative, but it seems the more liberal some people get the more conservative I become. " Link to comment Share on other sites More sharing options...
JohnnyG Posted September 17, 2004 Report Share Posted September 17, 2004 Most fuel guages are actually a wire wound resistor, with a float and a wiper. As the float moves up (as in a full tank) less resistance is in the circuit. The gauge actually ony gets more current due to less resistance in the circuit and reads full. Over time, several things can happen to a fuel guage wire. Corrosion due to chemicals in the fuel can affect the amount of oxidation on the wire surface, giving erroneous resistance readings and a false reading of the dash gauge. The wire that is the main resistor is usually silver plated to be as corrosion resistant as possible. The "wiping" action of the arm tends to keep the surface of the wire clean as the car travels over uneven roads and the fuel sloshes around in the tank. But, alas, over time the corrosion becomes too great or the resistance wire breaks somewhere in the middle and you get saome wierd readings. Keep in mind that the amount of current going through this wire is very small to prevent sparks from igniting the fuel in the tank, therefore only a slight amount of corrosion can affect the guages operation greatly. I suppose you could try to clean it...maybe even with some "Tarnex" once it is removed from the tank, but I'm sure you won't see that on any official GM repair manual. The best fix is to replace the sending unit. Throw in the On Board Diagnostics and who knows what things you might see from the gauge. Time to replace it. I didn't catch what year this car is. Never underestimate the amount of a persons greed. Link to comment Share on other sites More sharing options...
Frank Carbone Posted September 18, 2004 Author Report Share Posted September 18, 2004 Thanks for the replies. The car is a 1992 Seville SLS. One good thing is that I won't run out of fuel as when the gauge reads "E" there is still 25L of fuel in the tank. Thanks again Frank Link to comment Share on other sites More sharing options...
Rickster Posted January 22, 2005 Report Share Posted January 22, 2005 Did you ever replace your sending unit? 2001 STS Mettalic Otter Grey, Black Leather, 213,000 kilometers - miles - ? Still running strong! Link to comment Share on other sites More sharing options...
jhall Posted January 23, 2005 Report Share Posted January 23, 2005 That sounds like a classic case of a bad fuel sensor. Drop the tank, pull the pump, and replace the sensor. Note that if you ask for a "fuel sender" at the parts counter, you'll get a big $$ part that contains the sensor, but if the pump is working, all you need is the fuel sensor only - cost is about $100 if I remember correctly. Link to comment Share on other sites More sharing options...
jhall Posted January 23, 2005 Report Share Posted January 23, 2005 That sounds like a classic case of a bad fuel sensor. Drop the tank, pull the pump, and replace the sensor. Note that if you ask for a "fuel sender" at the parts counter, you'll get a big $$ part that contains the sensor, but if the pump is working, all you need is the fuel sensor only - cost is about $100 if I remember correctly. Link to comment Share on other sites More sharing options...
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