How long can gasoline sit inside a car fuel tank before it gets ruined or causes problems to injectors or fuel pump?

Depends some on gasoline and climate- Ethanol mixes are not known as long keepers and winters in snow belt can means condensation. Non ethanol gasoline with Brigges and Stratton stabilizer or SeaFoam can be good for a year, no stabilzer, cleaner and Ethanol gasoline means many motorcycles need drained gas tank and fresh fuel after a winter setting in Wisconsin. Snowmobile over summer may need just topped with fresh gas in early fall- but a extra years setting means carb check, drain fuel tank and SeaFoam and fresh non ethanol gas. Fuel pumps sometimes might get filter sock fouled, injectors less than a year shouldn't be a problem but Ethanol fuel can leave a 'varnish' that may foul tip holes.

If the car has been built since 1971, it can sit a very long time. In 1971 all autos sold new in the US were required to have sealed fuel systems to control evaporative emissions. I have bought a car that sat for almost two years and, after replacing the battery, it fired right up and ran smoothly.

Cars from the 1970s and 1980s might not start right up, though. Carburetors are not sealed and will let the volatile products needed for easy starting evaporate, and eventually the bowl can evaporate completely dry.

Several years with no problem. It might clog at any time.That's what there's a filter.

It will be fine. Pour 2 bottles of Heat gas treatment in the tank, then pour 2-3 gallons of fresh gas in.

Just get a hand pump, open the fuel cap and suck it out from the fuel port.

Pump fuel has a shelf life of 3-6 months.

How full is the tank? If it's 1/3 remaining or less, you could just fill it up with fresh fuel and you might be okay. Otherwise you can try to siphon most of it out first.

Take the fuel line off and jump the fuel pump relay and drain the tank at least to 1/4 tank. Then add 5 gallons of fresh gas.

The fuel tank has a small drain plug on the bottom. Make certain to catch the old fuel and don't let it go all over the ground. Use it in your lawn mower.

After ten months it is not fantastic in quality.There is no specific number of days minutes or seconds every tank a fuel remains good under every possible circumstance of weather and temperature.

Near full tank or near empty?

No one can guess how well you prepared you car BEFORE the long rest.

https://www.thoughtco.com/start-car-been-in-storag...

thats getting to the iffy stage .. gas generally 'starts' going bad after 4-5 months and after 6 its very questionable .. i'd say if its less than half a tank though top it up with fresh gas and maybe dump some sea foam in it to treat it and run it out .. if its MORE than half full of old gas i'd siphon most of it out .. if its bad and wont start you might have to crack the fuel line under the hood and turn the ignition on and pump the crud out of the lines until it gets to the tank mix ..