gas gauge might be inaccurate pump measuring isnt giving me a consistent feel on the accuarcy of the gas gauge. what the gauge has done:
jumped 1/2 down or up the gauge [eg: full to 1/2, 1/4 to 3/4 etc] off and back on fixes that sometimes
jumped by 1/4 at extended load 80+mph 3500 rpm
i get 300 per 3/4 tank(i always fill up at 1/4 though i did once run out of gas and have occasionally pushed it to 1/8 of a tank left]
but it read 1/4 left at 262 miles and took 14.4 gallons 13.3 is when the pump shut off.

ive been reading a chiltons manual and cant find anyway to test the fuel sending unit with a multimeter without dropping the tank
ive added a bottle of cleaner and changed the air filter 2 days ago haven't driven much since then.
and still have a full tank at 26 miles readout [normal for me]

1996 bonneville 3800 series II engine with 182k miles on it

If they gauge has been jumping around, then it sounds like the sender might be bad.

In the 92-99, replacement involves dropping the gas tank I believe.

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-Car Guy Carl
"Penelope" - 2003 SLE - 247k Miles
"Sydney" - 2000 Honda S2000 - 98k miles

i suspected that and have researched whats involved in replacing the pump and sender unit but is there a way to test it without dropping the tank (to confirm my suspicions)

if it is failing at least ill know in advance

edit: for clarity

99% sure your sending unit is bad. There are little fingers on the actual sending unit that break, causing the unit to send the incorrect amount of fuel to the gauge. Mine has been bad for a long time, so every time I fill up to get a full tank my gas gauge goes from full to empty and back for roughly the first 15 miles of the tank. I just reset my trip odometer because I don't have a way to drop the tank at my place. Replace the sending unit and you should be good to go.

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Joseph

Current: 2013 Infiniti G37 Journey
1999 Infiniti G20T - Sold
1999 Buick Lesabre - Race Couch - gone but not forgotten

2 questions
1. is there a wire somewhere not in the tank (there has to be one going out of the tank somewhere) that i can test with a multimeter to get an ohms reading to make sure its not a wiring issue to eliminate all other possibilities because i too cant drop the tank (if its bad id have to figure out how to drop the tank where i am)

2. for a replacement. would this be all thats needed parts wise? any specialised tools required etc?

The only wires are the wires to and from the connector that goes to the fuel pump.
I suppose you could backprobe the wires at the harness and see if resistance changes as you wiggle the wires.
Changing the fuel pump/sending unit is a pain and so you might want to invest in AC Delco parts or at least something a bit better than Spectra.
You truly don't want to have to do it twice.
It's very often recommended that you buy an AC Delco gasket for the fuel tank.
The reason is that the aftermarket gaskets are just an o-ring which can slip out of place while you reinstall the retaining ring.
The AC Delco part is a ring with tabs sticking out, which fit inside notches in the fuel tank.
You would be wise to use a brass punch to back off and install the fuel pump retainer.
This is due to the fact that brass, when struck with a hammer, will not make any sparks.
It can be impossible to unscrew the bolts that hold the fuel tank straps up.
The GM factory used cheap, rustable clips with a "sort-of" nut built in. I say sort-of because it has threads inside but isn't hexagonal on the outside.
I ended up cutting the bolts to drop the tank on my '93 because of this.

Sorry to chime in on this but my gauge has been a little goofy too. My gauge will jump or drop a 1/4 tank when I'm stopping or driving. Im not sure if its just BC of gas sloshing or if something is wrong. I can have a full tank and when I accelerate and typically anything over 40mph it will go about a 1/4 over full.

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Speed has never killed anyone, suddenly becoming stationary… that’s what gets you.