this problem has been very consistant with the chevrolet blazers and s10s as well.. my 88 s10 had the same problem with a standard, had the problem whenever i put the clutch in. fuel gauge then did not even work or jump with the clutch in. drove around for a year with no fuel gauge and only ran out of gas once or twice.. then the speedo went so i had no speedometer or odometer. never ran out of gas then . and just knew my speed by the rpm of the tach i put in and the gear i was in. never ran out and never got a speeding ticket.
sold the truck and bought a 2000 blazer and shortly the same problem began to happen. jumping around in park. but seeming to be fine otherwise. sometimes its a lil wierd with the brake on.

watch out because the fuel gauge seems to be normal in drive, it may sometimes read accurate from full to half a tank. and then not go below that, sometimes until you have 2litres left.
the problem lies in the fuel tank although you would think it to be a short. the metal contact plates on the sensors are made of to thin of metal and begin to corrode, making the connection vary and sometimes not work.. drop the fuel tank. take a look at the fuel pump as well because the fuel gauge going is usually an early indicator of a fuel pump to soon go. many lose their fuel pump within 6 months. and some go on forever, me i have been at a year. my s10 went a year and a half until the fuel pump died as well.
so if you want to spare the labour of doing both at seprate times just do them at the same time. or take a close inspection of the fuel pump.
talking with a guy that owns a repair shop in the city says it is very common with blazers. they usually come in for fuel pumps within6 months of a dead gauge.
if you are on the road and your fuel pump dies it will usually kick out, some early indicators are hesitatiton in acelleration as the poor connections do not allow full fuel pressure.
if you are on the road and it does die, get a friend to kick the gas tank while you turn the key, this sometimes can spark the connections and allow you to make it home or to a shop.

my blazer goes in to the shop next week to get the pump and sender done. i would normaly do this but i do not have the time. and the shop is very reasonable on labour rates.
rear springs for example cost me 220 cad for parts and installation.


as for fuel mileage ive maxed out at 600km highway. and am on average 350-400 city.
oddly when in the mountains i got better fuel economy than praries. and i have discoverd 105kmh to be more efficient than 100km or 110. but then again anything under 100km is usually better.

as for any of you wondering about the cheep chips that you can purchase on ebay that claim to give you more power and better fuel. they are simply a 6 ohm resistor that you plug into your air sensor. i found that i did not notice any more power, and it actually increased my fuel consumption an extra litre per 100km on average.

 

alright, gonna reply to this one, I recently replaced the sending unit/pump assembly. Job is a B(*())&& took me 13 hours in one day, FYI you will NOT be able to siphon ANY gas out, ther is a green plastic ball in the fill pipe. The job is doable tho.

 

Its not that hard unless the fastners are rusted in place. Then you gotta strip the threads or break the bolt in half. Takes a lot of torque. Prior to onwing an air gun this required a 3' long pry bar on my 1/2 rachet and lots of extensions so I could get the rachet below the axle. Plus a good breakfast of Wheeties. This is how I bent a 1/2 rachet. I got the gas tank out though. After wards I had an epifany. Next time I peel the carpet back and cut a hole in the floor.

 

Make sure you mark where the hole you cut is, and if there's any wires near by... For reference when my pump goes, lol.

This is where I envy the S10 guys, lol, they can just take the bed off.

 

Well, I'll be damned. My wife's '01 Jimmy does exactly the same thing. In Park, it says "E," no matter how much gas is in it. But once you put it in gear, it goes to where it's supposed to be. That does make me wonder if it was "normal" on that year of the GMC versions.

On the other hand, the gauge on my '96 Blazer wavers back and forth no matter what gear it's in, although I notice it goes more toward "E" when I'm on an upward slope. I don't believe my sending unit is gone yet, and I'm definitely not pulling off the tank any time soon. I'll worry about it when the fuel pump dies. LOL

Thanks to those who gave the advice...

 

exact same issue here. 01 blazer.

 

I have a 99 blazer and for about a year my fuel gauge has gone on the fritz i have to use the trip meter every time its very annoying. I especally hate the fact that i have neither the time nor the money to replace it. And yall who get over 300 miles to a tank thats crazy all i did was put a 2 inch lift and 31 x 10.5 mud tirers i only 12.5 mpg it really sucks cause i would hate to have to get rid of my blazer after all ive done to it just cause of gas.

 

Adjust your speedometer so it reads accurately... You'll probably get better mileage...

 

I have a 1996 4 door 4X4, I have had to replace the fuel pump twice in the last 5 years. prior to the first change everything was good. Since the first change the fuel gauge floats around depending on if you accelerating, going uphill or downhill. I thought that the second change would fix it, but it didn't. the first change was done with a GM part the second was from autozone I believe. could this be a problem in the tank with the baffle system, or perhaps a ground somewhere by the tank?

 

Quite possible it is a problem with the electrical connection to the vehicle. Did you have to splice in a new wiring connector when you replaced the pump?