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Most GM cars I have owned have had this problem, but not to the extreme my 94 Roadmaster does:

I get about 20mpg in boulevard driving. I have a 23 gal gas tank. At around 230-250 miles the needle is still above 7/8 full. Then from 230-250 miles to 530-550 miles it drops like a stone to Empty. So when it reads 7/8 full, I only have 1/2 a tank. left Is there an adjustment for this? My trip odometer is a far more reliable fuel gauge than my actual fuel gauge.

Oh, when I fill my tank the gauge goes way to the right of the full mark (something all GM cars I have ever seen do).

Whenever I fill my tank when the gauge reads 1/8 tank, I can get 22+ gallons in. Sometimes it is so close to 23, I am amazed I did not run out of gas. One time I made a sharp right turn under those conditions and it actually stalled. The gas must have sloshed away from the pickup tube temporarily.
 

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Thanks, if I ever have to replace my fuel pump, I will keep that procedure in mind! My 94 Fleetwood has a similar but less severe problem. I personally think they come from the factory with a degree of this problem. My late father had owned GM all his life, probably 100 or so cars, and he has told me that ALL the cars he has owned do this.

When I was restoring cars for fun, I have replaced several mid 60s to early 70s A body sending units with new ones, and even they display this problem.
 

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My 92 tank is empty when the pointer is on the last bar on the gauge. I fill mine when the pointer is at 1/2 on the gauge. The pointer stays pegged until I am down to about a half tank. My low fuel light and chime never activate. If it goes below the last bar, the pointer will reverse direction and show there is more fuel in the tank than actual.

I did a mod on my 91, and it has about 4 gallons left when the pointer is on the last bar. The low fuel light comes on and the chime sounds at about that same point.
 

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I've had a couple GM cars and 2 of them have had problems with the fuel gauge. I only have the 95 now but these are its symptoms; When I fill the tank it will take the needle about 15-20 miles to actually get to "Full," then it will stay at full until I reach about 70 miles, which then it will start to decline rapidly to just above the hash mark before "empty." It will stay exactly there until about 200 miles driven, then at 200 it will go down to empty and the low fuel light will come on. If I don't fill up before 300 miles the needle starts to climb back up away from empty. I usually fill up around 280 miles and it will put anywhere from 16 to 18 gallons back in. Definitely the weirdest acting one I've seen. :p
 

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Most GM cars I have owned have had this problem, but not to the extreme my 94 Roadmaster does:

I get about 20mpg in boulevard driving. I have a 23 gal gas tank. At around 230-250 miles the needle is still above 7/8 full. Then from 230-250 miles to 530-550 miles it drops like a stone to Empty. So when it reads 7/8 full, I only have 1/2 a tank. left Is there an adjustment for this? My trip odometer is a far more reliable fuel gauge than my actual fuel gauge.

Oh, when I fill my tank the gauge goes way to the right of the full mark (something all GM cars I have ever seen do).

Whenever I fill my tank when the gauge reads 1/8 tank, I can get 22+ gallons in. Sometimes it is so close to 23, I am amazed I did not run out of gas. One time I made a sharp right turn under those conditions and it actually stalled. The gas must have sloshed away from the pickup tube temporarily.
Driving around with that little gas is a recipe for frying the fuel pump. I never let it get below 1/4 tank. There is no point to trying to get X-miles out of a tank before filling it again. You can calculate your gas mileage without letting the tank get low.
 
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