only took 5.5gal.to fill tank to full bars-only got 205 miles & 'low gas warning light' came on?

This is a very common problem for the Gen 2 Prius. Do a search on this forum, and you will find your answer.

 

Well I'm going like 8.4 gallons for $345 mi something like that and when you say filling up to four bars or full bars what are you looking through the glass while you fill the car or are you filling it up till you till it shuts off or you filling it off till it shuts off and a few more squirts till you see the fuel at the top of the hole that you're putting the filler in? Generally I feel to the ladder all the way up until I can see the fuel right at that little hole I'm sticking the filler nozzle in and when the gas gets up to there everything is stopped that settles and it's right there about ready to fall out of where I put the cap on literally but I cap it off that's 8.4 gallons and I have driven about 345 355 miles and the display is telling me that I'm getting generally 40 mi to the gallon maybe 41.3. And now that's all changed it's jump back up 46 and a half after I change the fuel injectors like day before yesterday

 

Your gas gauge may need recalibrating or your bladder shrank and you're screwed outside of replacing it.

The gas guage reset chicken dance can be found on YouTube.

 

i read that there is a trick to fooling the full bladder, i will search for it

 

That does not "reset" the fuel gauge, it resets the inclination meters in the CM. The only real reason for doing that procedure is if you have just changed the CM.

No one ever mentions that the EVAP system might be messed up, which is the most likely reason. One way to do that is to top off the fuel so it is right at the top of the filler neck, thereby flooding the charcoal canister with fuel. Don't do that on these cars.

 

The Gen 2 Prius Prostate enlarges with age thus "reducing the volume of fluid" that the bladder can hold before the sensors kick in and give you a warning. You just have an 8.0 gallon tank now. It just is. You can buy a whole new gas tank and swap it out...not true for myself.

 

How much did it take to refill?

 

From a flashing pip and 20.miles on that flash I religiously put in 8.4 gallons just before fuels on my foot.this is every other day in my world. Sometimes two different gen2 both hold same to the tenth

 

My gas gauge became real inaccurate. I reset the inclination meter per the service manual and it solved my issue. I had previously pulled my dash out and maybe it recalibrated improperly after power loss or something. My hud is original.

 

Still can’t find that tip, will keep trying

 

By HUD, I assume you mean the combination meter. There is no HUD in the Gen 2.

There is likely a correlation between you pulling the dash out and the inclination meters needing resetting. This is an example of when it is appropriate to reset the inclination meters.

For most people with inaccurate fuel gauge readings, it usually points to the fuel sender (in the fuel tank) becoming flakey. This is easily tested to confirm the diagnosis. Unfortunately, for the NA model, the fix for this is a new fuel tank.

 

Check the wheels to see if the brakes are dragging

 

Where is the car in Vermont or Florida If you're in Florida should be starting to get warm now Just keep pounding gas in it and park it in the Sun My bladder has stretched out to the point where I can drop 8.4 gallons on high when I bought the car I was putting about 4.7 in it It would kick off I'm in North Carolina gets pretty hot I just kept filling the car up it's kind of parked in the sunny on my property and you know about two three months of doing that drive it a little run it on service calls in the summer It's hot as all get out outside like I say now I can drop 8.4 in it on full blast

 

Inclination Sensors.

There are two inclination sensors located in the [fuel] meter ECU to
detect vehicle longitudinal and latitudinal inclinations and to correct
the fuel level calculation. Corrections are made by the signals from
the inclination sensors and the ambient temperature sensor located
in the fuel tank.

The inclinometer must be reset if the customer complains that they
can only pump a few gallons of gas into their tank or if they run out
of gas with three or four bars left on the fuel meter. The inclinometer
must also be reset if the Prius is refilled on an excessive slope or if
the fuel gauge becomes inaccurate. Please refer to the Prius Repair
Manual for the inclometer calibration procedure.

This is from the Toyota tech training manual.

 

It sounds like a "Hail Mary" what have you got to lose approach, although the comment about if the car was filled up on an excessive slope is interesting. It would almost imply there is some kind of finessing of the sensor data going on.

Anyway, if it works, as it did for you, then all well and good. It is just 95% of the feedback we get on here says it does not fix the problem.

 

The signal from the sensor in the fuel tank comes to the instrument panel of the combined indicator.
In this case, one of them is not telling the truth.
It is worth conducting a check procedure.

https://share.qclt.com/%E4%B8%B0%E7%94%B0%E6%99%AE%E7%91%9E%E6%96%AF%E5%8E%9F%E5%8E%82%E8%8B%B1%E6%96%87%E6%89%8B%E5%86%8Cpdf%E6%A0%BC%E5%BC%8F/repair%20manual/04pruisr/05/215dw/cimg5.pdf