2000 neon 249948 mile loosing fuel enco and power

Nikki is the engine light on, are there any codes,have you had a tune up or any other work done lately.when you say it won't start when warm(do you mean engine will not turn over, or does engine turn and refuses to fire.
If I had to guess failing fuel pump, they tend not to build fuel pressure when ran a while(warmed up) and when left to cool build somewhat better pressure.
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Is Your Fuel Pump Going Bad
How do know if its fuel filter or fuel pump that is causing the problem
How To Diagnose Fuel Pump Failure EricTheCarGuy
http://www.clarks-garage.com/shop-manual/ts-01.htm#hot-start

If you have done basic tune up stuff, I would check fuel pressure with gauge installed and running down the highway. Other possibles are bad ignition module, loose wire somewhere in coil circuit, bad fuel pump, filter, many others.

CODE P1684 - BATTERY HAS BEEN DISCONNECTED.LOOK FOR LOOSE BATTERY CONNECTIONS. ARE BATTERY ITSELF HAS CELL PLATES SHORT INSIDE OF IT. CODE PO171 - FUEL SYSTEM LEAN. CODE PO462 - FUEL LEVEL SENSOR NUMBER 1 LOW INPUT. ALL YOUR PROBLEMS HAS TO DO WITH CODE P1684. CHECK BATTERY HAVE IT LOAD TESTED AND CHECK BATTERY CABLES FOR TIGHTNESS.TO KEEP FROM LOCKING OUT RADIO TURN IT OFF FIRST BEFORE YOU DISCONNECT NEGATIVE BATTERY CABLE.

Published performance of the 2000 Dodge Neon is 27 MPG (Miles per US Gallon) for mixed City/Highway driving which translates to 8.7 Liters per 100Km.

Hope the information is useful.

Follow the hanes manual and you will have no problem. Also I have a 2000 neon and the origional transmission working great. I change the fluid and filter and adjust the bands every 30,000 miles

You could very well have a pump that is weak and loses some of it's pumping power after it has gotten fully warmed up. Have you ever noticed a temporary improvement in power after refiling with cool fuel? A test drive with a fuel pressure gauge should tell the tale about pump condition. Usually a restricted filter will cause a starvation problem all the time instead of just after a long drive. It certainly wouldn't hurt to change the filter but I doubt that it is your problem.

are you getting fire to the spark plugs and fuel to the injectors or fuel rail? timing belts on them are bad to break around 80 to 90k miles

Has the vehicle had a tune up since it was new? I would start with that and a fuel system service. Fuel filter could be clogged or the fuel pump may be weak. This may help you with your problem without knowing the history of the vehicle.

1 Inspect Throttle Position Sensor Faulty or Incorrectly Connected Throttle Position Sensor.
2 Inspect Mass Air Flow Sensor Damaged, Loose, or Faulty Mass Air Flow Sensor or Circuit.
3 Inspect Choke Thermostat Stuck or Improperly Functioning Choke Thermostat.
4 Inspect Air Cleaner Tempature Sensor Damaged or Faulty Air Cleaner Tempature Sensor.
5 Inspect Fuel Filter Clogged or Dirty Fuel Filter.
6 Inspect PCV Valve Plugged or Damaged PCV Valve.
7 Inspect Carburetor Worn, Faulty or Damaged Carburetor.
8 Inspect Fuel Injector Dirty or Worn Fuel Injectors.
9 Inspect Hose (PCV)at Clogged or Collapsed PCV Hoses.
10 Inspect Fuel Pump Faulty Fuel Pump.
11 Inspect Fuel Pump Low Fuel Pressure.

Try cleaning out your intake (get some stp throttle body cleaner) try running some fuel cleaner through you gas tank, check you air filter. maybe you could replace your spark plugs and wires. these are just a couple of things I could think of that could cause it.