* Water in the Fuel: Three years of sitting allows moisture to condense in the tank. When fresh gas is added, it mixes with the water, and the water can disrupt the fuel pump's ability to draw fuel or cause immediate stalling. The water can also clog the fuel filter.
* Clogged Fuel Filter: Years of sitting can allow sediment and varnish to build up in the fuel filter, restricting fuel flow. The added fresh gas might temporarily dislodge some of this debris, causing it to block fuel lines further down the system.
* Bad Fuel Pump: The fuel pump may have failed due to age and lack of use. The pump might work briefly before overheating or failing completely, especially under the added stress of trying to pump a mix of old and new fuel.
* Clogged Fuel Injectors: Similar to the fuel filter, injectors can become clogged with varnish and debris. The new fuel might temporarily dislodge this blockage, but the system won't function properly for long.
* Corroded Fuel Tank: After three years, the inside of the fuel tank may have corroded, causing debris to contaminate the fuel and affecting fuel flow.
* Other Issues: While less likely, there are other possibilities like a faulty crankshaft position sensor, ignition problems (though less probable if it starts at all), or issues with the fuel pressure regulator. However, the symptoms strongly point to fuel system problems.
Troubleshooting Steps (in order of likelihood and easiest to check):
1. Drain a Small Amount of Fuel: Carefully siphon out a small amount of fuel from the tank. Look for water in the fuel. Water will settle to the bottom and appear as a separate layer.
2. Replace the Fuel Filter: This is cheap and relatively easy to do. A clogged filter is a high probability given the car's age and inactivity.
3. Check the Fuel Pump: This may require some mechanical knowledge and specialized tools. You might need to test the fuel pressure to see if the pump is delivering adequate fuel pressure. A weak or failing pump is also very plausible.
4. Inspect the Fuel Injectors: This is more advanced and might require professional help. They may need to be cleaned or replaced.
5. Examine the Fuel Tank: If possible, inspect the fuel tank for corrosion. This might require dropping the tank, so it's best left to a mechanic.
Important Safety Note: Working with fuel is hazardous. Always work in a well-ventilated area, away from open flames or sparks. Consider wearing safety glasses and gloves. If you're not comfortable working on your car yourself, take it to a qualified mechanic.
The combination of old fuel and a three-year dormant period makes a complete fuel system checkup highly advisable before attempting extensive driving. Addressing the fuel system issues is crucial before moving on to more complex diagnostics.
